BIOL 314 Final

Question 1

Maintaining pH and salt concentrations is critical to keeping proteins functional. What is the molecular mechanism by which pH affects protein function?

-Only the primary structure is altered, which changes the folding and function of the protein.
-A few of the polar R-groups can change charge, and the new attraction or repulsion can alter the shape of the protein.
-The hydrogen bonds within the polypeptide backbone that form the secondary structures are completely disrupted.
-The N- and C-terminus amino acids with their amino and carboxyl ends can change the shape of the entire protein.

Answer 1

A few of the polar R-groups can change charge, and the new attraction or repulsion can alter the shape of the protein.

Question 2

Which of the following is NOT a feature commonly observed in α helices?

-cylindrical shape
-left-handedness
-1 helical turn every 3.6 amino acids
-amino acid side chains that point outward

Answer 2

left-handedness

Question 3

Two or three α helices can sometimes wrap around each other to form coiled-coils. The stable wrapping of one helix around another is typically driven by __________ interactions.

hydrophilic
hydrophobic
ionic
van der Waals

Answer 3

hydrophobic

Question 4

The three-dimensional coordinates of atoms within a folded protein are determined experimentally. After researchers obtain a protein’s structural details, they can use different techniques to highlight particular aspects of the structure. What visual model best displays a protein’s secondary structures (α helices and β sheets)?

space-filling
ribbon
backbone
wire

Answer 4

ribbon

Question 5

Cyclic AMP (cAMP) is a small molecule that associates with its binding site with a high degree of specificity. Which types of noncovalent interactions are the most important for providing the “hand in a glove” binding of cAMP?

hydrophobic interactions
electrostatic interactions
hydrogen bonds
van der Waals interactions

Answer 5

hydrogen bonds

Question 6

Some proteins have α helices, some have β sheets, and still others have a combination of both. What makes it possible for proteins to have these common structural elements?

specific amino acid sequences
side-chain interactions
the hydrophobic-core interactions
hydrogen bonds along or between strands of the protein backbone

Answer 6

hydrogen bonds along or between strands of the protein backbone

Question 7

The variations in the physical characteristics between different proteins are influenced by the overall amino acid compositions, but even more important is the unique amino acid

sequence.
bond.
number.
orientation.

Answer 7

sequence

Question 8

Proteins bind selectively to small-molecule targets called ligands. The selection of one ligand out of a mixture of possible ligands depends on the number of weak, noncovalent interactions in the protein’s ligand-binding site. Where is the binding site typically located in the protein structure?

buried in the interior of the protein
on the surface of the protein
inside a cavity on the protein surface
on the surface of the protein in the presence of ligand

Answer 8

inside a cavity on the protein surface

Question 9

In the polypeptide sequence shown below, which letter represents the peptide bond?

bond between c=o and n-h bonds, removes the h from nh2 and oh from cooh to form bond

Figure 4-2

C
A
B
D

Answer 9

C

Question 10

Complete the sentence with the best option provided below. The primary structure of a protein is the

lowest energy conformation.
amino acid sequence.
amino acid composition.
average size of amino acid side chains.

Answer 10

amino acid sequence

Question 11

A lab has sequenced a novel cancer-causing gene in humans. What can we learn from the protein sequence by inputting the predicted protein sequence into a computer and conducting bioinformatic analysis?

the rate at which the protein will be degraded
how many protein-binding partners it will have, including its quaternary structure
the complete tertiary structure of this protein
how to predict the domains by matching the amino acids with another similar sequence

Answer 11

how to predict the domains by matching the amino acids with another similar sequence

Question 12

Polypeptides are synthesized from amino acid building blocks. The condensation reaction between the growing polypeptide chain and the next amino acid to be added involves the loss of a(n)

carbon atom.
carboxylic acid group.
water molecule.
amino group.

Answer 12

water molecule

Question 13

Cells utilize several mechanisms for restricting the movement of membrane proteins within the plasma membrane. One of these mechanisms allows cells to form specialized attachment structures called focal adhesions to promote cell motility. Which of the following mechanisms describes how motile cells form focal adhesions on the plasma membrane?

Proteins are tethered to the cell cortex.
Proteins are tethered to the proteins on the surface of another cell.
Proteins are tethered to the extracellular matrix.
Protein movement is limited by the presence of a diffusion barrier.

Answer 13

Proteins are tethered to the extracellular matrix.

Question 14

Which of the following types of lipids is the most abundant in the plasma membrane?

phospholipids
sterols
triacylglycerides
glycolipids

Answer 14

phospholipids

Question 15

Porin proteins form large, barrel-like channels in the membrane. Which of the following statements about these channels is FALSE?

They are made primarily of β sheets.
They cannot form narrow channels.
They have alternating hydrophobic and hydrophilic amino acids.
They are made primarily of α helices.

Answer 15

They are made primarily of α helices.

Question 16

New membrane phospholipids are synthesized by enzymes bound to the __________ side of the __________ membrane.

luminal; Golgi
cytosolic; mitochondrial
cytosolic; endoplasmic reticulum
extracellular; plasma

Answer 16

cytosolic; endoplasmic reticulum

Question 17

Consider a transport vesicle containing a membrane glycoprotein. The glycoprotein and the vesicle’s phospholipids are delivered to the plasma membrane, as shown in the figure below. Which of the following is an accurate description of the outcome of this process?

Figure 11-4

-The portion of the glycoprotein that was inside of the vesicle ends up in the cytosol after it is delivered to the plasma membrane.
-Some of the individual phospholipid molecules are released into the cytosol to prevent the plasma membrane, and thus the cell, from becoming too large.
-The phospholipids that are delivered to the noncytosolic face of the plasma membrane used to be in the interior (luminal) face of the vesicle.
-The fusion event between the vesicle and the plasma membrane randomizes the phospholipids between the cytosolic and noncytosolic faces of the bilayer.

Answer 17

The phospholipids that are delivered to the noncytosolic face of the plasma membrane used to be in the interior (luminal) face of the vesicle.

Question 18

Which of the following is most likely to occur after the lipid bilayer is pierced?

The membrane expands.
The membrane reseals.
A tear forms.
The membrane collapses.

Answer 18

The membrane reseals

Question 19

Which of the following substances is most commonly used to help purify a membrane protein?

sucrose
ethanol
high salt solution
detergent

Answer 19

detergent

Question 20

Cholesterol serves several essential functions in mammalian cells. Which of the following is NOT influenced by cholesterol?

membrane permeability
membrane fluidity
membrane thickness
membrane rigidity

Answer 20

membrane thickness

Question 21

Cells utilize several mechanisms for restricting the movement of membrane proteins within the plasma membrane. One of these mechanisms allows cells to present antigens to other cells to trigger the adaptive immune response. Which of the following mechanisms describes how antigen-presenting cells perform this function?

Proteins are tethered to the cell cortex.
Proteins interact with the proteins on the surface of another cell.
Protein movement is limited by the presence of a diffusion barrier.
Proteins are tethered to the extracellular matrix.

Answer 21

Proteins interact with the proteins on the surface of another cell. (other cells)

Question 22

A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of fluidity in its cell (plasma) membrane?

decrease the amount of cholesterol in the membrane
add lipids with hydrocarbon tails that are shorter and have more double bonds
add lipids with hydrocarbon tails that are longer and have fewer double bonds
decrease the number of glycolipids in the membrane

Answer 22

add lipids with hydrocarbon tails that are shorter and have more double bonds

Question 23

Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold?

All channels open completely.
A few channels remain closed and most open completely.
All channels open partly, each to a different degree.
All channels open partly, to the same degree.

Answer 23

A few channels remain closed and most open completely

Question 24

Which of the following occur without coupling transport of the solute to the movement of a second solute?

the export of Na+ from cells to maintain resting membrane potential
export of Ca2+ from the cytosol
export of H+ from animal cells for pH regulation
export of glucose out of gut epithelial cells

Answer 24

export of glucose out of gut epithelial cells

Question 25

Some cells express aquaporin proteins—they are channel proteins that facilitate the flow of water molecules through the plasma membrane. What regulates the rate and direction of water diffusion across the membrane?

resting membrane potential
aquaporin conformation
availability of ATP
the concentration of water on either side of the membrane

Answer 25

the concentration of water on either side of the membrane

Question 26

If the K+ concentration increases in extracellular space, the membrane potential of a cell will become

repolarized.
hyperpolarized.
depolarized.
stabilized, because the membrane is not permeable to K+.

Answer 26

depolarized.

Question 27

Transporters, in contrast to channels, work by

filtering solutes by size.
specific recognition of transport substrates.
filtering solutes by charge.
a gating mechanism.

Answer 27

specific recognition of transport substrates.

Question 28

Negatively charged ions are required to balance the net positive charge from metal ions such as K+, Na+, and Ca2+. Which of the following negatively charged ions is the most abundant outside the cell and which ion most often counterbalances the negative charge (written in parentheses)?

Cl- (Na+)
PO43- (K+)
PO43- (Ca2+)
Cl- (Ca2+)

Answer 28

Cl- (Na+)

Question 29

Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion?

OH-
HCO3-
Cl-
PO43-

Answer 29

Cl-

Question 30

Pumps are transporters that can harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called

free diffusion.
passive transport.
active transport.
facilitated diffusion.

Answer 30

active transport

Question 31

If a chemical blocks the voltage-gated K+ channels in an action potential, which region of the action potential will be the most affected?

Figure 12-3

A
B
D
C

Answer 31

C (repolarization phase )

Question 32

Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is NOT one of the common ways to perform active transport?

K+-coupled
light-driven
ATP-driven
Na+-coupled

Answer 32

K+-coupled

Question 33

As living cells grow and form complex communities in their environment, which statement describes entropy (or disorder) in a way that is consistent with the second law of thermodynamics?

The entropy inside the cell increases as cells grow.
The entropy in the environment decreases as cells grow.
The entropy in the environment increases as cells grow.
The entropy in the cells and the environment is unchanged as cells grow.

Answer 33

The entropy in the environment increases as cells grow.

Question 34

Macromolecules in the cell can often interact transiently as a result of noncovalent interactions. These weak interactions also produce stable, highly specific interactions between molecules. Which of the factors below is the most significant in determining whether the interaction will be transient or stable?

the rate of synthesis
surface complementarity between molecules
the concentration of each molecule
the size of each molecule

Answer 34

surface complementarity between molecules

Question 35

The synthesis of glutamine from glutamic acid requires the production of an activated intermediate followed by a condensation step that completes the process. Both amino acids are shown in Figure 3-4.

oh on glu switched for a nh2, acitvation step involves atp
Figure 3-4

Which molecule is added to glutamic acid in the activation step?

ADP
ATP
NH3
phosphate

Answer 35

ATP

Question 36

Lysozyme is an enzyme that specifically recognizes bacterial polysaccharides, which render it an effective antibacterial agent. Into what classification of enzymes does lysozyme fall?

protease
nuclease
hydrolase
isomerase

Answer 36

hydrolase

Question 37

Proteins can assemble to form large complexes that work coordinately, like moving parts inside a single machine. Which of the following steps in modulating the activity of a complex protein machine is LEAST likely to be directly affected by ATP or GTP hydrolysis?

translation of protein components
complex disassembly
conformational change of protein components
complex assembly

Answer 37

translation of protein components

Question 38

Which of the following statements is true?

The sequence of the atoms in the polypeptide backbone varies between different proteins.
Nonpolar amino acids tend to be found in the interior of proteins.
There is free rotation around all covalent bonds in the polypeptide backbone.
Peptide bonds are the only covalent bonds that can link two amino acids in proteins.

Answer 38

Nonpolar amino acids tend to be found in the interior of proteins.

Question 39

Which of the following statements is true?

Disulfide bonds stabilize but do not change a protein’s final conformation.
Disulfide bonds are formed mainly in proteins that are retained within the cytosol.
Disulfide bonds are formed by the cross-linking of methionine residues.
Disulfide bonds are more common for intracellular proteins, compared to extracellular proteins.

Answer 39

Disulfide bonds stabilize but do not change a protein’s final conformation.

Question 40

The correct folding of proteins is necessary to maintain healthy cells and tissues. The presence of unfolded proteins is associated with some neurodegenerative disorders such as Alzheimer’s disease, Huntington’s disease, and Creutzfeldt–Jakob disease (the specific faulty protein is different for each disease). What happens to these disease-causing, unfolded proteins?

They form structured filaments.
They bind a different target protein.
They form protein aggregates.
They are degraded.

Answer 40

They form protein aggregates.

Question 41

Which of the following statements is true regarding the behavior of lipids in cell membranes?

Membrane lipids diffuse laterally within the plane of the membrane.
The hydrocarbon tails of membrane lipids act like stiff rods.
Membrane lipids frequently flip-flop between one monolayer and the other.
Individual lipids tumble end over end within a single monolayer.

Answer 41

Membrane lipids diffuse laterally within the plane of the membrane.

Question 42

Which of the following functions of the plasma membrane is possible without membrane proteins?

intercellular communication
import/export of molecules
cellular movement
selective permeability

Answer 42

selective permeability

Question 43

How does a bilayer arrangement of phospholipids result in higher entropy for the system and thus make membrane formation energetically favorable?

Polar head groups form a hydrogen-bonding network at the interface with water.
Fatty acid tails are highly saturated and flexible.
Water molecules form cagelike structures around hydrophobic molecules, thus encouraging the latter to cluster together and limit their contact with water.
Hydrogen bonds form between neighboring polar head groups in the bilayer.

Answer 43

Water molecules form cagelike structures around hydrophobic molecules, thus encouraging the latter to cluster together and limit their contact with water.

Question 44

Which of the following membrane lipids does not contain a fatty acid tail?

phosphatidylserine
a glycolipid
cholesterol
phosphatidylcholine

Answer 44

cholestrol

Question 45

Which of the following mechanisms best describes the process by which nutrients are taken up selectively at the apical surface and then released from the basal and lateral surfaces of the epithelial cells that line the gut?

Proteins are tethered to the proteins on the surface of another cell.
Protein movement is limited by the presence of a diffusion barrier.
Proteins are tethered to the extracellular matrix.
Proteins are tethered to the cell cortex.

Answer 45

Protein movement is limited by the presence of a diffusion barrier.

Question 46

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant outside a typical mammalian cell?

Na+
K+
Cl-
Ca2+

Answer 46

Na+

Question 47

The Na+-K+ pump has been inhibited in the gut epithelial cells with a chemical like ouabain. What will happen to glucose transport on the apical membrane, and why?

Glucose transport will stay the same, because the Na+ gradient is not involved in the transport of glucose.
Inward glucose transport will increase because the outward K+ electrochemical potential will decrease.
Inward glucose transport will slowly decrease into the epithelial cells because of the slow accumulation in intracellular Na+.
Inward glucose transport will increase because of the higher electrochemical potential of Na+.

Answer 47

Inward glucose transport will slowly decrease into the epithelial cells because of the slow accumulation in intracellular Na+.

Question 48

Which of the following statements about resting membrane potential is true?

The resting membrane potential for most animal cells is zero mV, because the positive and negative ions are in balance.
The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell.
At the resting membrane potential, no ions enter or exit the cell.
The resting membrane potential for most animal cells is positive, because Na+ ions are so plentiful inside cells.

Answer 48

The resting membrane potential for most animal cells is negative, because the inside of the cell is more negatively charged than the outside of the cell.

Question 49

Below is a list of molecules with different chemical characteristics. Knowing that all molecules will eventually diffuse across a phospholipid bilayer, select the option below that most accurately predicts the relative rates of diffusion of the following molecules (fastest to slowest):

alanine estrogen propanol sodium

sodium > propanol > alanine > estrogen
estrogen > propanol > sodium > alanine
alanine > propanol > sodium > estrogen
estrogen > propanol > alanine > sodium

Answer 49

estrogen > propanol > alanine > sodium

Question 50

Coiled coils are defined by all of the following EXCEPT:

-Coiled coils are the hallmark of Alzheimer’s disease, forming the amyloid fibrils found in diseased brains.
-they coil together due to their amphipathic nature
-Two or even sometimes three heptad repeat coils wind together to form a superhelical bundle
-they are comprised of “heptad repeats” where the 1st and 4th amino acids are hydrophobic

Answer 50

Coiled coils are the hallmark of Alzheimer’s disease, forming the amyloid fibrils found in diseased brains.

Question 51

Two or three α helices can sometimes wrap around each other to form coiled-coils. The stable wrapping of one helix around another is typically driven by
__________ interactions.

hydrophilic
ionic
van der Waals
hydrophobic

Answer 51

hydrophobic

Question 52

Advantages of protein phosphorylation as a regulatory mechanism include all of
the following EXCEPT:

-It changes the chemical nature of S,T,Y, and H R-group sidechains from polar to basic in nature.
-It can trigger allosteric changes to alter activity
-Several different amino acids can be phosphorylated, meaning that a protein could be
regulated by different kinases and at different sites, increasing the potential complexity of
signaling
-Depending on the context, phosphorylation can be used to positively regulate or negatively regulate a protein

Answer 52

-It changes the chemical nature of S,T,Y, and H R-group sidechains from polar to basic in nature.

Question 53

Regulation of a protein’s activity by the binding of a small nucleotide such as ATP or GTP has all of the advantages below EXCEPT:

-Its small size allows it to diffuse rapidly to the protein, a key advantage to speed up “multi-step” processes
-its binding can cause allosteric changes in the protein that regulate its activity
-it modifies a single amino acid on the protein it regulates, increasing the number of different options for regulatory complexity if it can bind more than one site
-it can positively or negatively regulate the protein’s interaction with other proteins, depending on the context

Answer 53

-it modifies a single amino acid on the protein it regulates, increasing the number of different options for regulatory complexity if it can bind more than one site

Question 54

Fluorescence recovery after photobleaching (FRAP) is a way to measure:

Mobility of a protein within the cell
The free energy of a protein.
The equilibrium constant for a given reaction
Change in the membrane potential

Answer 54

Mobility of a protein within the cell

Question 55

Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks?

phospholipases
flippases
convertases
glycosylases

Answer 55

flippases

Question 56

Most animal fats form a solid at room temperature, while plant fats remain liquid at room temperature. Which of the following is a feature of lipids in plant membranes that best explains this difference?

higher levels of sterols
larger head groups
unsaturated hydrocarbons
longer hydrocarbon tails

Answer 56

unsaturated hydrocarbons

Question 57

Which of the following statements is TRUE?

Membrane lipids diffuse within the plane of the membrane.
In eukaryotes, all membrane-enclosed organelles are surrounded by one lipid bilayer.
In an aqueous environment, the formation of liposomes by phospholipids requires energy.
Membrane lipids frequently flip-flop between one monolayer and the other

Answer 57

Membrane lipids diffuse within the plane of the membrane.

Question 58

Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes?

rotation around the long axis of a fatty acid
moving between lipid layers
flexing of hydrocarbon chains
lateral movement

Answer 58

moving between lipid bilayers

Question 59

Why does the part of the polypeptide chain that crosses the lipid bilayer of most transmembrane proteins usually exist as an alpha helix or beta barrel?

-Because a rigid structure such as occurs with these conformations is needed to penetrate through a lipid bilayer.
-Because in both an alpha helix or a beta barrel the polar peptide bonds of the polypeptide backbone chain are H-bonded and completely shielded from the hydrophobic
environment of the lipid bilayer by the hydrophobic amino acid side chains.
-Because these secondary structures always form the correct length needed to traverse a lipid bilayer (20-24 amino acids)
-Because both of these secondary structures are able to shield their polar groups away from the hydrophobic lipid bilayer due to the van der Waals forces.

Answer 59

Because in both an alpha helix or a beta barrel the polar peptide bonds of the polypeptide backbone chain are H-bonded and completely shielded from the hydrophobic
environment of the lipid bilayer by the hydrophobic amino acid side chains.

Question 60

A similarity between symporters and antiporters is:

Both transporters are responsive to the membrane potential, opening once threshold is reached.
Both transporters couple the movement of two different solvents across the cell membrane.
Both transporters operate using passive transport mechanisms.
Both transporters are coupled to ATP hydrolysis to drive solute transport across the membrane.

2.5 ptsQuestion 36
free diffusion.
passive transport.
(Q013) Pumps are transporters that are able to harness energy provided by other
components in the cells to drive the movement of solutes across membranes,
against their concentration gradient. This type of transport is called

Answer 60

Both transporters couple the movement of two different solvents across the cell membrane.

Question 61

A transporter protein that is also described as a “pump”:

Always hydrolyzes ATP to function
Is specialized to allow ions to move through an open pore in response to a signal that triggers an allosteric change that opens the pore.
Operates via a passive transport mechanism to transport solutes from high concentration to low.
uses energy to transport a solute against its concentration or electrochemical gradient

Answer 61

uses energy to transport a solute against its concentration or electrochemical gradient

Question 62

The three ways that an ion channel can be gated include:

ligand-gated, voltage-gated, mechanically- (stress-) gated.
ligand-gated, ATP-gated, membrane-gated
temperature-gated, voltage-gated, NAD+ -gated
RNA-gated, diffusion-gated, osmotic pressure-gated

Answer 62

ligand-gated, voltage-gated, mechanically- (stress-) gated.

Question 63

Which of the following channels would not be expected to generate a change in voltage by movement of its substrate across the membrane where it is found?

a sodium channel
a proton channel
a calcium channel
an aquaporin

Answer 63

an aquaporin

Question 64

Which of the following statements about the ER network is NOT true?

The ER produces proteins that are sent to other organelles such as the Golgi, lysosomes, and the plasma membrane.
The ER is the most extensive membrane system in eukaryotic cells.
The ER is dynamic so tubules can be formed where needed.
The ER produces proteins that are sent out of the ER to many areas of the cytosol.

Answer 64

The ER produces proteins that are sent out of the ER to many areas of the cytosol.

Question 65

Which of the following organelles is not part of the endomembrane system?
lysosomes
Golgi apparatus
the endosome
mitochondria

Answer 65

mitochondria

Question 66

Mitochondria and chloroplasts are different from all other organelles in that they:
Use SNARE proteins to tether them to their proper locations in the cell
Possess their own small genomes and can make some of their own proteins
Are able to bud transport vesicles to remove toxic waste build-up
Have a symmetric single lipid bilayer surrounding them

Answer 66

Possess their own small genomes and can make some of their own proteins

Question 67

ATP is important for chaperone protein function. Why would protein import into mitochondria be disrupted if ATP were depleted from inside mitochondria?

The protein would be blocked from entering the translocation apparatus
The translocation apparatus would be unable to function without ATP hydrolysis
The protein could slip back out of the mitochondria during transport
The signal sequence would not be recognized on the mitochondrial protein

Answer 67

The protein could slip back out of the mitochondria during transport

Question 68

Proteins that are fully translated in the cytosol do not end up in
the interior of the nucleus.
transport vesicles.
the cytosol.
the mitochondria.

Answer 68

transport vesicles

Question 69

Which of the following statements about vesicle budding from the Golgi is FALSE?
Adaptins interact with clathrin.
Clathrin molecules are important for binding to and selecting cargoes for transport.
Once vesicle budding occurs, clathrin molecules are released from the vesicle.
Clathrin molecules act at the cytosolic surface of the Golgi membrane.

Answer 69

Clathrin molecules are important for binding to and selecting cargoes for transport.

Question 70

Which of the following statements about phagocytic cells in animals is FALSE?
Phagocytic cells extend pseudopods that surround the material to be ingested.
Phagocytic cells scavenge dead and damaged cells and cell debris.
Phagocytic cells are important in the gut to take up large particles of food.
Phagocytic cells can engulf invading microorganisms and deliver them to their lysosomes for destruction.

Answer 70

Phagocytic cells are important in the gut to take up large particles of food.

Question 71

Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels?
ER → Golgi → plasma membrane
lysosome → endosome → plasma membrane
Golgi → lysosome → plasma membrane
ER → lysosome → plasma membrane

Answer 71

ER → Golgi → plasma membrane

Question 72

Which of the following is not unfolded during its import?
Proteins imported into the chloroplast
Proteins imported into the nucleus.
Proteins imported into the ER
Proteins imported into the mitochondria

Answer 72

Proteins imported into the nucleus.

Question 73

v-SNARES participate directly in:
movement of the vesicle along cytoskeletal filaments
uncoating of the vesicle
docking of the vesicle to the target organelle
assembly or formation of the transport vesicle

Answer 73

docking of the vesicle to the target organelle

Question 74

A key mechanism to bring a vesicle to a specific target membrane for fusion is:
Phosphorylation of t-SNAREs and v-SNAREs that unmask their binding domains that bring the vesicle close to the target membrane
Interaction of coiled coil domains on v-SNARES and t-SNARES that ratchet the two membranes, bringing them increasingly close until they fuse
Phospholipases on the naked transport vesicle will cleave the target membrane to allow fusion
Signal sequences on the clathrin coat are recognized by a docking protein on the target membrane

Answer 74

Interaction of coiled coil domains on v-SNARES and t-SNARES that ratchet the two membranes, bringing them increasingly close until they fuse

Question 75

Which of the following statements is TRUE?
The signal sequences on mitochondrial proteins are usually at the C-terminus.
Most mitochondrial proteins are not imported from the cytosol but are synthesized inside the mitochondria.
Mitochondrial proteins cross the membrane in their native, folded state.
Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.

Answer 75

Chaperone proteins in the mitochondria facilitate the movement of proteins across the outer and inner mitochondrial membranes.

Question 76

If you cloned a gene into a cell that encodes a protein with an ER signal sequence at its N-terminus and a nuclear localization sequence in its middle, where will the expressed protein be found?
in the nucleus
In the ER lumen
Half will be in the ER and half will be in the nucleus
It will be degraded in the lysosome

Answer 76

In the ER lumen

Question 77

Which of the following statements about transport into mitochondria and chloroplasts is FALSE?

Proteins that are transported into these organelles are unfolded as they are being transported.
Signal peptidase will remove the signal sequence once the protein has been imported into these organelles.
After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane.
The signal sequence on proteins destined for these organelles is recognized by a receptor protein in the outer membrane of these organelles.

Answer 77

After a protein moves through the protein translocator in the outer membrane of these organelles, the protein diffuses in the lumen until it encounters a protein translocator in the inner membrane.

Question 78

All of the following targeting sequences are cleaved off during the import process EXCEPT:
The mitochondrial targeting sequence
The ER signal sequence
the nuclear localization sequence
The chloroplast targeting sequence

Answer 78

the nuclear localization sequence

Question 79

Which of the following statements about nuclear transport is TRUE?
Nuclear import receptors bind to proteins in the cytosol and bring the proteins to the nuclear pores, where the proteins are released from the receptors into the pores for transit into the nucleus.
Nuclear pores are made up of many copies of a single protein.
Nuclear pores contain proteins with disordered segments that fill the channel and allow small water-soluble molecules to pass through in a non-selective fashion.
mRNAs and proteins transit the nucleus through different types of nuclear pores.

Answer 79

Nuclear pores contain proteins with disordered segments that fill the channel and allow small water-soluble molecules to pass through in a non-selective fashion.

Question 80

Sorting information that directs trafficking or localization within the cell may be found on all of the following EXCEPT:
NLS
SNARE protein
chaperone
signal sequence

Answer 80

chaperone

Question 81

Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP. What is the most likely effect of this drug on nuclear transport?
Nuclear transport receptors would be unable to bind cargo.
Nuclear transport receptors would be unable to enter the nucleus.
Nuclear transport receptors would be unable to release their cargo in the nucleus.
Nuclear transport receptors would interact irreversibly with the nuclear pore fibrils.

Answer 81

Nuclear transport receptors would be unable to release their cargo in the nucleus.

Question 82

One of the three types of GTP-binding proteins, often called “G-proteins”, are membrane bound. These are the:
trimeric GTP-binding proteins
monomeric GTP-binding proteins
G-protein coupled receptors
Elongation factor GTP-binding proteins

Answer 82

trimeric GTP-binding proteins

Question 83

What enzymatic activity does a G protein have?
GTPase activity
Phosphatase activity
Translocase activity
Kinase activity

Answer 83

GTPase activity

Question 84

Which of the following is NOT true?
G proteins can hydrolyze GTP on their own but it is very slow
GDIs are necessary for G proteins to release GDP so they can bind GTP
G proteins can release GDP on their own but at an extremely slow rate
GAP proteins stimulate the rate of GTP hydrolysis by a G protein

Answer 84

GDIs are necessary for G proteins to release GDP so they can bind GTP

Question 85

GTPase switch proteins such as ras:
Are converted from the active to inactive state by a guanine nucleotide exchange factor
are active when bound to GTP but inactive when bound to GDP
are active when bound to GDP but inactive when bound to GTP
synthesize GTP from GDP

Answer 85

are active when bound to GTP but inactive when bound to GDP

Question 86

The Src homology 2 domain (SH2) binds:
cAMP
phosphorylated phosphinositol phospholipid
phosphotyrosine
proline-rich motif

Answer 86

phosphotyrosine

Question 87

Which of the following describes negative feedback regulation?
a component acts to further activate the signaling pathway and enhance the cell’s response
A component generates an all-or-none, switch-like mechanism
A component amplifies the signal for a more robust response
a component late in the pathway inhibits an enzyme early in the pathway

Answer 87

a component late in the pathway inhibits an enzyme early in the pathway

Question 88

Which of the following signaling pathways would be likely to trigger the most rapid cell response?

Adrenaline binds to a GPCR to activate a cyclic AMP signaling pathway that triggers glycogen breakdown
Acetylcholine binds to anion-channel-coupled receptor that allows Na+ to flow down its electrochemical gradient, triggering contraction of a skeletal muscle cell.
Nerve growth factor binds to a receptor tyrosine kinase to activate a signaling pathway that enhances the transcription of Bcl2, a protein that suppresses cell death
Platelet-derived growth factor binds to a RTK to activate a signaling pathway that stimulates cell proliferation at the site of a wound

Answer 88

Acetylcholine binds to anion-channel-coupled receptor that allows Na+ to flow down its electrochemical gradient, triggering contraction of a skeletal muscle cell.

Question 89

Which of the following types of cell signaling is long range and uses hormones as signals?
paracrine
neuronal
endocrine
contact-dependent

Answer 89

endocrine

Question 90

RTKs can activate the enzyme phosphoinositide 3-kinase, which phosphorylates inositol phospholipids. These phospholipids then do what?

activate G proteins
serve as phosphate donors in phosphorylation reactions
serve as a docking site that recruit specific intracellular signaling proteins to the plasma membrane
activate ras

Answer 90

serve as a docking site that recruit specific intracellular signaling proteins to the plasma membrane

Question 91

Which type of cell-surface receptor(s), when activated, catalyze(s) a reaction inside the cell?
G-protein coupled receptors
enzyme-coupled receptors
ion-channel-coupled receptors
enzyme-coupled receptors AND G-protein coupled receptors

Answer 91

enzyme-coupled receptors

Question 92

Which of the following statements about G-protein-coupled receptors (GPCRs) is FALSE?
GPCRs are the largest family of cell-surface receptors in humans.
GPCRs are used in endocrine, paracrine, and neuronal signaling.
The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.
GPCRs are found in yeast, mice, and humans.

Answer 92

The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

Question 93

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a
dissolved gas.
neurotransmitter.
hormone.
scaffold.

Answer 93

hormone.

Question 94

(Q029) When the cytosolic tail of the __________ receptor is cleaved, it migrates to the nucleus and affects gene regulation.
Notch
G-protein coupled
nuclear
growth factor

Answer 94

Notch

Question 95

Which of the following statements is TRUE?
A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response.
To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol.
Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.
Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

Answer 95

Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

Question 96

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in __________ signaling.
contact-dependent
neuronal
paracrine
endocrine

Answer 96

contact-dependent

Question 97

All members of the nuclear receptor family
do not undergo conformational changes.
interact with signal molecules that diffuse through the plasma membrane.
are cell-surface receptors.
are found only in the cytoplasm.

Answer 97

interact with signal molecules that diffuse through the plasma membrane.

Question 98

A protein kinase can act as an integrating device in signaling if it
is activated by two or more proteins in different signaling pathways.
initiates a phosphorylation cascade involving two or more protein kinases.
phosphorylates more than one substrate.
catalyzes its own phosphorylation.

Answer 98

is activated by two or more proteins in different signaling pathways.

Question 99

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization?
a mutation that prevents RGFR from binding to RGF
changing the tyrosines that are normally phosphorylated on RGFR dimerization to alanines
changing the tyrosines that are normally phosphorylated on RGFR dimerization to glutamic acid
a mutation that increases the affinity of RGFR for RGF

Answer 99

a mutation that prevents RGFR from binding to RGF

Question 100

You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells?
addition of a drug that activates adenylyl cyclase
addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive
addition of a drug that prevents GTP hydrolysis by Gα
addition of a drug that mimics the ligand of ERC1

Answer 100

addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive

Question 101

The enzyme that synthesizes cAMP is:
cyclooxygenase
polyadenylase
guanylyl cyclase
adenylyl cyclase

Answer 101

adenylyl cyclase

Question 102

The drug Viagra promotes blood vessel dilation by prolonging signaling through nitric oxide (NO). How does Viagra boost NO?

It binds to acetylcholine receptors on endothelial cells
It prevents acetylcholine from ginding to its receptors
It blocks the enzyme that degrades cyclic GMP
It blocks the enzyme that degrades cyclic AMP

Answer 102

It blocks the enzyme that degrades cyclic GMP

Question 103

What type of cell response would take the longest amount of time (on the scale of minutes to hours) to execute?
one that uses a phosphorylation event to activate an enzyme
one that involves the firing of an action potential along a neuron
one that involves the release of secretory vesicles
one that involves a change in gene expression

Answer 103

one that involves a change in gene expression

Question 104

The following happens when a G-protein-coupled receptor activates a G protein.
The GDP bound to the α subunit is phosphorylated to form bound GTP.
The α subunit exchanges its bound GDP for GTP.
It activates the α subunit and inactivates the βγ complex.
The β subunit exchanges its bound GDP for GTP.

Answer 104

The α subunit exchanges its bound GDP for GTP.

Question 105

Which of the following statements is TRUE?
Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type.
Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.
A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response.
To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol.

Answer 105

Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

Question 106

A key function of the Golgi apparatus is:
translation of membrane-bound and secreted proteins
modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelle
oxidative breakdown of toxic molecules
intracellular degradation

Answer 106

modification, sorting, and packaging of proteins and lipids for either secretion or delivery to another organelle

Question 106

All of the following are true about lysosomes EXCEPT:
Lysosomes contain a broad spectrum of hydrolytic enzymes that are only active in the very basic (i.e., high pH) environment of the lysosome
Some ligand-bound receptors are targeted to the lysosome for degradation after internalization, while other types may be recycled to the membrane for reuse
Lysosomes contain proton pumps that are necessary to maintain an acidic environment in this compartment
Lysosomes can degrade many cellular components, including proteins, lipids, and nucleic acids

Answer 106

Lysosomes contain a broad spectrum of hydrolytic enzymes that are only active in the very basic (i.e., high pH) environment of the lysosome

Question 106

Proteins typically included in coated vesicles include:
nuclear import receptor
nitrous oxide
adaptins
cAMP

Answer 106

adaptins

Question 107

N-linked oligosaccharides on secreted glycoproteins are attached to
the asparagine in the sequence Asn-X-Ser/Thr.
the N-terminus of the protein.
nitrogen atoms in the polypeptide backbone.
the serine or threonine in the sequence Asn-X-Ser/Thr.

Answer 107

the asparagine in the sequence Asn-X-Ser/Thr.

Question 108

Researchers studying yeast discovered that, for some mutants, when the temperature at which the cells are grown was elevated from 25 degrees Celsius to 37 degrees Celsius, their secretory pathway no longer functions and the cells grow dense with unsecreted proteins.

When these cells are examined microscopically, they can be divided into groups that vary in terms of where the unsecreted proteins accumulate. In some of the mutants, proteins accumulate in the ER; in others, the Golgi; in others, they accumulate in vesicles near the plasma membrane.

What is the likely explanation for this difference in appearance?

The temperature-sensitive mutant proteins are targeted to different compartments
Different temperature-sensitive mutations disrupt protein synthesis
Different temperature-sensitive mutations affect different stages of the transport process
Different temperature-sensitive mutations promote an increase in protein synthesis

Answer 108

Different temperature-sensitive mutations affect different stages of the transport process

Question 109

Many viruses enter cells through receptor-mediated endocytosis. Which of the following strategies could be effective in blocking entry of this class of viruses into cells and could be used to treat viral infections?

Increase the activity of clathrin
Block the function of adaptin
Block the actin filaments
Block the receptor with an antibody

Answer 109

Block the receptor with an antibody

Question 110

Which of the following is NOT required for targeting and import of a mitochondrial protein?
a signal recognition particle (SRP) that recognizes the signal sequence and arrests translation until the ribosome can dock at the mitochondrial translocator
protein unfolding during translocation
an N-terminal amphipathic targeting signal sequence
involvement of chaperones to unfold and refold the protein before and during mitochondrial import

Answer 110

a signal recognition particle (SRP) that recognizes the signal sequence and arrests translation until the ribosome can dock at the mitochondrial translocator

Question 111

You are interested in Fuzzy, a soluble protein that functions within the ER lumen. Given that information, which of the following statements must be TRUE?
Fuzzy must contain a hydrophobic stop-transfer sequence.
Only one ribosome can be bound to the mRNA encoding Fuzzy during translation.
Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.
Fuzzy has a C-terminal signal sequence that binds to SRP.

Answer 111

Once the signal sequence from Fuzzy has been cleaved, the signal peptide will be ejected into the ER membrane and degraded.

Question 112

Neutrophils are phagocytic cells found in our immune system. Which of the following characteristics are specific to phagocytosis, such as that performed by neutrophils, compared to other methods of endocytosis?

Is a constitutive process generally continually happening in animal cells
Uses clathrin-coated vesicles to engulf a target
Generally used to engulf large targets like microorganisms and cell debris
Requires receptor-clustering into a coated pit

Answer 112

Generally used to engulf large targets like microorganisms and cell debris

Question 113

Mechanisms to target proteins to the correct compartment include all of the following EXCEPT:
Transport by protein translocators.
Transport through an aquaporin beta barrel
Transport by vesicles.
Gating through a pore.

Answer 113

Transport through an aquaporin beta barrel

Question 113

G protein signaling can be regulated by other proteins that include all of the following EXCEPT:
cAMP
GAP
GDI
GEF

Answer 113

cAMP

Question 114

The role of a GAP protein in a signaling pathway is:
To activate an inactivated G protein
To inactivate an activated G protein
To generate the IP3 second messenger
To generate a phosphorylated tyrosine binding site that recruits an adaptor protein

Answer 114

To inactivate an activated G protein

Question 115

In a trimeric G protein, what makes the G-alpha subunit separate from the G-beta/G-gamma?
Interaction with a GDI
Binding of GTP
Phosphorylation
Binding of GDP

Answer 115

Binding of GTP

Question 116

A typical signaling pathway for a steroid hormone involves:
Steroid hormone crosses membrane to bind intracellular (or intranuclear) receptor –> receptor undergoes allosteric change –> receptor now acts as a transcription factor to turn on gene expression
Steroid hormone activates nitric oxide synthase to produce NO –> NO diffuses to neighboring muscle cells –> muscle relaxation is triggered
Steroid hormone binds to GPCR –> trimeric G protein is activated to produce cAMP and Ca2+ second messengers –> effector proteins activated to change cytoskeleton and cell morphology
Steroid hormone binds to RTK –> activation of RTK promotes assembly of signaling complex –> signaling complex activates a kinase cascade –> different effector proteins change cell behavior

Answer 116

Steroid hormone crosses membrane to bind intracellular (or intranuclear) receptor –> receptor undergoes allosteric change –> receptor now acts as a transcription factor to turn on gene expression

Question 117

Effector proteins can include all of the following EXCEPT:
transcription factor
cytoskeletal protein
metabolic enzyme
cAMP

Answer 117

cAMP

Question 118

Which of the following statements is TRUE?
PI 3-kinase phosphorylates a lipid in the plasma membrane.
Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP.
Dimerization of GPCRs leads to Gα activation.
MAP kinase is important for phosphorylating MAP kinase kinase.

Answer 118

PI 3-kinase phosphorylates a lipid in the plasma membrane.

Question 119

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by
activating a G protein.
activating a receptor tyrosine kinase.
diffusing into cells and stimulating the cyclase directly.
activating an intracellular protein kinase.

Answer 119

diffusing into cells and stimulating the cyclase directly.

Question 120

All of the following are examples of second messengers EXCEPT:
IP3
Na+
cAMP
Ca2+

Answer 120

Na+

Question 121

A key function of the endosome is:
sorting of endocytosed material
secretion of neurosecretory hormones
synthesis of most lipids and membrane proteins
oxidative breakdown of toxic materials

Answer 121

sorting of endocytosed material

Question 122

Which of the following statements about the endoplasmic reticulum (ER) is FALSE?
The ER membrane is contiguous with the outer nuclear membrane.
The ER is the major site for new membrane synthesis in the cell.
Proteins to be delivered to the ER lumen are synthesized on the smooth ER.
Steroid hormones are synthesized on the smooth ER.

Answer 122

Proteins to be delivered to the ER lumen are synthesized on the smooth ER.

Question 123

Which of the following is NOT a process that delivers material to the lysosome?
transcytosis
pinocytosis
phagocytosis
autophagy

Answer 123

transcytosis

Question 124

Which of the following statements about a protein in the lumen of the ER is FALSE?
-A protein in the lumen of the ER is synthesized by ribosomes on the ER membrane.
-Some of the proteins in the lumen of the ER can end up in the lumen of an organelle in the endomembrane system.
-Some of the proteins in the lumen of the ER can end up in the plasma membrane.
-Some of the proteins in the lumen of the ER can end up in the extracellular space.

Answer 124

Some of the proteins in the lumen of the ER can end up in the plasma membrane.

Question 125

Which of the following statements is TRUE?
-Proteins destined for the ER are translated by a special pool of ribosomes whose subunits are always associated with the outer ER membrane.
-Proteins destined for the ER are translated by a pool of cytosolic ribosomes that
contain ER-targeting sequences that interact with ER-associated protein
translocators.
-Proteins destined for the ER are translated by cytosolic ribosomes and are
targeted to the ER when a signal sequence emerges during translation.
-Proteins destined for the ER translocate their associated mRNAs into the ER
lumen where they are translated

Answer 125

Proteins destined for the ER are translated by cytosolic ribosomes and are targeted to the ER when a signal sequence emerges during translation.

Question 126

A large protein that passes through the nuclear pore must have an appropriate
-sorting sequence, which typically contains the positively charged amino acids lysine and arginine.
-sequence to interact with the nuclear fibrils.
-Ran-interacting protein domain.
-sorting sequence, which typically contains the hydrophobic amino acids leucine and isoleucine.

Answer 126

sorting sequence, which typically contains the positively charged amino acids lysine and arginine.

Question 127

All of the following are true about clathrin-coated vesicles EXCEPT:
Receptor-mediated endocytosis often occurs via clathrin-coated vesicles
Specificity of cargo is determined by clathrin binding
As cargo/cargo receptor/adaptin/clathrin complexes come together, clathrin interactions bend
the membrane into what is called a “coated pit”
A protein called dynamin is necessary to pinch off the vesicle from the membrane

Answer 127

Specificity of cargo is determined by clathrin binding

Question 128

Vesicles from the ER enter the Golgi at the
trans Golgi network.
cis Golgi network.
medial cisternae.
trans cisternae.

Answer 128

cis Golgi network.

Question 129

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in the
mitochondria.
interior of the nucleus.
cytosol.
nuclear membrane.

Answer 129

cytosol

Question 130

Examples of endocytosis include all the following EXCEPT:
transcytosis
uptake of glucose from the intestinal lumen
phagocytosis
pinocytosis

Answer 130

uptake of glucose from the intestinal lumen

Question 131

When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is TRUE?
The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras.
The cells you create will run out of the GTP necessary to activate Ras.
The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly.
The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras

Answer 131

The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras

Question 132

Which of the following is NOT true?
Addition of a phosphoryl group on a protein adds two negative charges to the protein
Trimeric G proteins are inactive when they exist as a trimer
Binding of GTP to a G protein will always result in its activation
Phosphorylation of a protein will always result in its activation

Answer 132

Phosphorylation of a protein will always result in its activation

Question 133

Trimeric G proteins:
Are active when they exist as a trimer
Do not interact with 7-transmembrane-domain receptor proteins (also known as GPCRs)
Are only active when all the subunits separate so they can act independently
Bind a guanine nucleotide in their alpha subunit

Answer 133

Bind a guanine nucleotide in their alpha subunit

Question 134

The pleckstrin homology (PH) domain binds:
proline-rich motif
phosphoserine
phosphorylated inositol phospholipid
phosphotyrosine

Answer 134

phosphorylated inositol phospholipid

Question 135

Akt promotes the survival of many cells by affecting the activity of Bad and
Bcl2, as diagrammed in Figure 16-28.
Figure 16-28
Which of the following statements is FALSE?
In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein
Bcl2.
In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active.
In the absence of a survival signal, Bad is phosphorylated.
In the presence of a survival signal, Akt is phosphorylated.

Answer 135

In the absence of a survival signal, Bad is phosphorylated.

Question 136

Which of the following statements is FALSE?
Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription.
Some signal molecules are transmembrane proteins.
Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.
Nucleotides and amino acids can act as extracellular signal molecules

Answer 136

Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.

Question 137

During fertilizaton:
A GPCR is activated that signals a kinase to initiate transcription to inhibit polyspermy
No signaling can occur until after the sperm nucleus has fused with the egg nucleus
Na+ channels open to trigger an action potential to inhibit polyspermy
Rapid diffusion of a wave of Ca2+ across the egg inhibits polyspermy

Answer 137

Rapid diffusion of a wave of Ca2+ across the egg inhibits polyspermy

Question 138

The cytoskeletal system characterized as being a thin, flexible, helical polymer that may sometimes be bundled or branched is:
actin filaments
microtubules
intermediate filaments
myosin thick filaments

Answer 138

actin filaments

Question 139

Rigor mortis occurs in muscle cells after death and is characterized by muscles being locked in a contracted state where myosin is bound to actin. What could be added to the muscle cell to release the rigor state?

Pi
ADP
ATP
ADP + Pi

Answer 139

ATP

Question 140

Which of the following would be a consequence of mutations that disrupt the interaction between cross-linking, stabilizing proteins and keratin filaments?

neurodegeneration caused by an interference with normal axonal transport
corneal damage caused by cell rupture from mechanical trauma
defects in muscle development caused by improper organization of sarcomeres
skeletal and cardiac abnormalities caused by a weakened nuclear envelope

Answer 140

corneal damage caused by cell rupture from mechanical trauma

Question 141

Which of the following would increase the level of muscle contraction?

addition of a molecule to bind free Ca2+
mutation in troponin such that it no longer binds tropomyosin
inactivation of the myosin motor
blockage of the Ca2+ pump

Answer 141

blockage of the Ca2+ pump

Question 142

Motor neuron degeneration occurs in several diseases and leads to loss of muscle control. One form of motor neuron degeneration was found to have defects in retrograde transport (backward transport to cell body, in blue below) that were caused by mutations in a gene that codes for a particular protein.
(backward is toward -, outward is toward +)
What protein, when mutated, would inhibit backward, but not outward, transport along axon microtubules?

dynein
tubulin
kinesin
myosin

Answer 142

dynein

Question 143

Mutation of the muscle-specific intermediate filament desmin leads to the rare disease desmin-related myopathy. This disorder starts with weakness of the lower limbs when patients are in their 20s or 30s. As symptoms worsen, weakness in respiratory and cardiac muscles occurs, which can lead to serious problems including sudden cardiac arrest.

Mutations that disrupt desmin intermediate filament structure or function could explain the symptoms of desmin-related myopathy. Possible mutations that may result in this disease include all of the following EXCEPT.

Alteration in head groups, so tetramers are unable to link end to end.
Mutation such that formation of dimers is blocked.
Alteration in the twist or coiling of the dimers, blocking formation of staggered tetramers.
Disruption of the polarity of the final desmin strands.

Answer 143

Disruption of the polarity of the final desmin strands.

Question 144

For both actin and microtubule polymerization, nucleotide hydrolysis is important for

stabilizing the filaments once they are formed.
promoting nucleation of filaments.
decreasing the binding strength between subunits on filaments.
increasing the rate at which subunits are added to the filaments.

Answer 144

decreasing the binding strength between subunits on filaments.

Question 145

An actin-binding protein called cofilin binds preferentially to ADP-containing actin filaments rather than ATP-containing actin filaments. Based on this preference, which is true?

Cofilin competes with profilin for binding to actin.
Cofilin binds to the plus ends of treadmilling actin filaments.
Cofilin binds to the plus ends of actin filaments
Cofilin binds to older actin filaments.

Answer 145

Cofilin binds to older actin filaments.

Question 146

Which of the following statements about the structure of microtubules is FALSE?

Microtubules are built from protofilaments that come together to make a hollow structure.
α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.
The two ends of a protofilament are chemically distinct, with α-tubulin exposed at one end and β-tubulin exposed at the other end.
Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity.

Answer 146

α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.

Question 147

Which of the following structures shorten during muscle contraction?

myosin filaments
sarcomeres
actin filaments
flagella

Answer 147

sarcomeres

Question 148

If GTP hydrolysis occurs on a tubulin molecule at the plus end of a microtubule protofilament before another tubulin molecule is added, what typically happens?

The microtubule remains the same size.
The microtubule polymerizes.
The microtubule depolymerizes.
The GDP is rapidly exchanged for a fresh molecule of GTP.

Answer 148

The microtubule depolymerizes.

Question 149

Shown below is the structure of a bipolar mitotic spindle. Which element(s) is/are the k-fibers?
(none of the elements in the photo are considered k-fibers)
C
A
none of these
B

Answer 149

none of these

Question 150

Kinesin-5 is a motor protein that binds to overlapping interpolar microtubules near the midzone of the mitotic spindle. Each of these kinesin proteins has two motor domains that walk toward the plus ends of the microtubules to which the kinesin is bound. When is this kinesin active and how does it affect the spindle?

During anaphase A, kinesin-5 slides the microtubules past one another toward the spindle poles, pushing the poles apart and lengthening the spindle.
During anaphase A, kinesin-5 slides the microtubules past one another toward the spindle poles, pulling the poles together and shortening the spindle.
During anaphase B, kinesin-5 slides the microtubules past one another toward the spindle poles, pulling the poles together and shortening the spindle.
During anaphase B, kinesin-5 slides the microtubules past one another toward the spindle poles, pushing the poles apart and lengthening the spindle.

Answer 150

During anaphase B, kinesin-5 slides the microtubules past one another toward the spindle poles, pushing the poles apart and lengthening the spindle.

Question 151

Different cyclin-dependent protein kinases (Cdks) trigger different stages of the cell cycle in part because

Their activities increase at different stages of the cycle.
All of the answers are correct about the cyclin-dependent kinases.
Their concentrations increase at different stages of the cycle.
They are degraded at different stages of the cycle.

Answer 151

Their activities increase at different stages of the cycle.

Question 152

Levels of Cdk activity change during the cell cycle, in part because

Cdk degradation precedes entry into the next phase of the cell cycle.
the Cdks activate the cyclins.
cyclin levels change during the cycle.
the Cdks phosphorylate each other.

Answer 152

cyclin levels change during the cycle.

Question 153

Which of the following statements about kinetochores is TRUE?

Kinetochores assemble on chromosomes that lack centromeres.
Kinetochores assemble onto chromosomes during late prophase.
Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules.
Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome.

Answer 153

Kinetochores assemble onto chromosomes during late prophase.

Question 154

At the end of DNA replication, the sister chromatids are held together by the

kinetochores.
securins.
histones.
cohesins.

Answer 154

cohesins

Question 155

Which of the following events does NOT usually occur during interphase?

The centrosomes are duplicated.
The nuclear envelope breaks down.
Cells grow in size.
DNA is replicated.

Answer 155

The nuclear envelope breaks down.

Question 156

Which of the following statements is FALSE?

Cdc25 dephosphorylation of Wee1 activates the kinase, promoting the G2/M transition.
The activating phosphatase (Cdc25) removes the phosphates from mitotic Cdk that were added by Wee1, so that M-Cdk will be active.
Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive.
Inhibiting the Cdc25 phosphatase will delay the G2/M transition.

Answer 156

Cdc25 dephosphorylation of Wee1 activates the kinase, promoting the G2/M transition.

Question 157

Which letter is associated with the line that is pointing to the interpolar microtubules in Figure 18-29?
(E is the poles between the the center and the centrioles)
C
E
D
B

Answer 157

E

Question 158

The concentration of mitotic cyclin (M cyclin)

is activated by phosphorylation.
falls toward the end of M phase as a result of ubiquitylation and degradation.
is highest in G1 phase.
is constant during M phase but its phosphorylation by Cdk increases its activity.

Answer 158

falls toward the end of M phase as a result of ubiquitylation and degradation.

Question 159

The chemotherapy drug paclitaxel is used to treat ovarian and breast cancers. One action of Paclitaxel is to bind to and decrease the activity of Bcl-2. How does this result in the death of cancer cells, helping to treat the cancer?

Paclitaxel promotes apoptosis of the cancer cell.
Paclitaxel blocks assembly of the kinetochore on the centromere.
Paclitaxel disrupts the structure and integrity of the nucleus, leading to cell death.
Paclitaxel inhibits cytokinesis, leading to multinucleate cells.

Answer 159

Paclitaxel promotes apoptosis of the cancer cell.

Question 160

The expression levels of different __________ fluctuate throughout the cell cycle.
cyclins and Cdks
phosphates
Cdks
cyclins

Answer 160

cyclins

Question 161

Which of the following is a TRUE statement?
Cells having an intermediate filament network that cannot be depolymerized would die.
The plus ends of microtubules grow faster because they have a larger GTP cap.
Kinesin moves endoplasmic reticulum (ER) membranes along microtubules so that the network of ER tubules becomes stretched throughout the cell.
GTP is hydrolyzed by tubulin to cause the bending of flagella.

Answer 161

Kinesin moves endoplasmic reticulum (ER) membranes along microtubules so that the network of ER tubules becomes stretched throughout the cell.

Question 162

Which of the following is TRUE regarding the role of Ca2+ in muscle contraction?
Ca2+ release is required for the refractory stage that returns the muscle to its pre-contraction state.
Ca2+ binding to myosin causes it to release from actin.
Ca2+ binds troponin, causing it to move tropomyosin and thereby expose actin filaments to myosin heads.
Ca2+ binding is required to maintain the structure of the actin filament.

Answer 162

Ca2+ binds troponin, causing it to move tropomyosin and thereby expose actin filaments to myosin heads.

Question 163

What would happen in a mutant cell that cannot degrade M cyclin?
The cell would complete division but would arrest permanently in G1.
The cell would complete division but would enter G0.
The cell would enter mitosis but would be unable to exit mitosis.
The cell cannot undergo the metaphase-anaphase transition.

Answer 163

The cell would enter mitosis but would be unable to exit mitosis.

Question 164

The slow rise of S cyclin levels throughout G1 phase is due to ________, and the abrupt decrease is caused by __________.
phosphorylation; translation
transcription; proteolysis
synthesis; mitosis
import; export

Answer 164

transcription; proteolysis

Question 165

Cohesin is cleaved by the enzyme ________, which is held in an inactive state by _________ until it is degraded by the APC/C complex.
separase; securin
nuclease; M-Cdk
separase; kinetochores
securin; separase

Answer 165

separase; securin

Question 165

What is a reasonable explanation for why there are no known motor proteins that move on intermediate filaments?
Intermediate filaments are bundled; motor proteins can only walk on a single protofilament.
Intermediate filaments are too dynamic so they would likely fall apart before a motor protein could get to its target.
Intermediate filaments have no polarity so their ends are chemically indistinguishable.
Intermediate filaments are rope-like and so would not be rigid enough, like microtubules are, to support a motor protein.

Answer 165

Intermediate filaments have no polarity so their ends are chemically indistinguishable.

Question 166

A small amount of cytoplasm from a mitotic cell is injected into an unfertilized frog oocyte, causing the oocyte to enter M phase. A sample of this oocyte’s cytoplasm is then injected into a fresh unfertilized oocyte, causing it to enter M phase. This is repeated many times until it is clear that none of the cytoplasm from the original mitotic cell can still be present in the newly injected unfertilized oocyte. Why then does cytoplasm from the newly injected unfertilized oocyte trigger mitosis when injected into yet another unfertilized (and thus non-dividing) oocyte?

Injection into an oocyte breaks the membrane, much like when a sperm penetrates, which is the signal to enter M phase. So it is the actual injection that triggers M-phase, not the cytoplasm.
Because only trace amounts of the M-phase cytoplasm are needed, and the experiment was not done sufficiently long enough to dilute out this trace activity.
Because injection into an oocyte perturbs the tensegrity of the cytoskeletal elements, which activates M-phase in order to repair the cytoarchitecture of the oocyte.
M-phase cytoplasm contains activated M-Cdk, which will activate the inactive M-Cdk already present in the oocyte. Thus, each round of injections perpetuates this activation of pre-existing inactive M-Cdk.

Answer 166

M-phase cytoplasm contains activated M-Cdk, which will activate the inactive M-Cdk already present in the oocyte. Thus, each round of injections perpetuates this activation of pre-existing inactive M-Cdk.

Question 167

Which of the following is a TRUE statement?

Without actin, cells can form a functional mitotic-spindle and pull their chromosomes apart but cannot divide.
Dynein moves the lamellipodia and filopodia along the cell’s substratum so they can act as “feelers” to find anchor points.
The transverse tubules in a muscle cell are extensions of the endoplasmic reticulum.
Activation of myosin movement on actin filaments is triggered by the phosphorylation of troponin in some situations and by Mg2+ binding to troponin in others.

Answer 167

Without actin, cells can form a functional mitotic-spindle and pull their chromosomes apart but cannot divide.

Question 168

Which of the following correctly matches the phase of the eukaryotic cell with an event that takes place in that phase?
G1 phase - DNA synthesis
M phase - cytokinesis
S phase - cell growth
G2 phase - mitosis

Answer 168

M phase - cytokinesis

Question 169

In terms of structure, if cytoplasmic intermediate filaments are described as ropes, nuclear lamins could be best described as:
vesicles
cylinders
string
mesh

Answer 169

mesh

Question 170

In which phase of mitosis does the nuclear envelope break down?
anaphase
telophase
prometaphase
metaphase

Answer 170

prometaphase

Question 171

What determines the position of the cleavage furrow of the dividing cell?
Astral microtubules contact the membrane and activate proteins to form a central furrow.
The interpolar microtubules send signals to form a cleavage furrow between the poles.
The cleavage furrow position is determined randomly.
The two spindle poles send signals to the plasma membrane so that the cleavage furrow forms in the same plane as the two poles.

Answer 171

The interpolar microtubules send signals to form a cleavage furrow between the poles.

Question 172

All of the following is true about cyclins EXCEPT:
cyclins have no intrinsic enzymatic activity
cyclins bind Cdk’s to help activate them
chaperones guide cyclins to the proteosome for degradation
cyclin concentration varies during the cell cycle

Answer 172

chaperones guide cyclins to the proteosome for degradation

Question 173

Where is Ca2+ stored inside a muscle cell?
Golgi apparatus
neurosecretory vesicles
mitochondria
sarcoplasmic reticulum

Answer 173

sarcoplasmic reticulum

Question 174

The cytoskeletal system characterized as being comprised of rigid, hollow cylinders are:
myosin thick filaments
actin filaments
intermediate filaments
microtubules

Answer 174

microtubules

Question 175

Which of the following statements about the function of the centrosome is FALSE?

Centrosomes contain hundreds of copies of the gamma-tubulin ring complex important for microtubule nucleation.
Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules.
Centrosomes are the major microtubule-organizing center in animal cells.
Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.

Answer 175

Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.

Question 176

Which of the following statements about microtubules is TRUE?

Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell.
The centromere nucleates the microtubules of the mitotic spindle.
ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.
Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.

Answer 176

Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.

Question 177

Kinesins and dyneins

often move in opposite directions to each other.
have tails that bind to the filaments.
move along both microtubules and actin filaments.
derive their energy from GTP hydrolysis.

Answer 177

often move in opposite directions to each other.

Question 178

Which of the following questions about the cytoskeleton is FALSE?

Covalent bonds between protein monomers hold together the cytoskeletal filaments.
The cytoskeleton is made up of three types of protein filaments.
The cytoskeleton of a cell can change in response to the environment.
The cytoskeleton controls the location of organelles in eukaryotic cells

Answer 178

Covalent bonds between protein monomers hold together the cytoskeletal filaments.

Question 179

Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure 17-20. Notice that the two types of cargo are traveling in opposite directions. Which of the following statements is likely to be FALSE?

The black cargo moving toward the axon terminal contains a domain that specifically interacts with the tail domain of a particular kind of motor.
The black cargo and the gray cargo require ATP hydrolysis for their motion.
The gray cargo is attached to dynein.
The black cargo and the gray cargo are moving along microtubules of opposite polarity.

Answer 179

The black cargo and the gray cargo are moving along microtubules of opposite polarity.

Question 180

What must happen at the end of the microtubule in order for it to stop shrinking and start growing again?

Interaction with ARP in order to seed a branch point
Addition of a sufficient number of GTP-loaded tubulin subunits to the growing end to quickly cover up the GDP-containing subunits
Phosphorylation of tau protein so it will bind and stabilize the microtubule
Once a microtubule starts shrinking, it must completely disassemble before a new microtubule can start growing again.

Answer 180

Addition of a sufficient number of GTP-loaded tubulin subunits to the growing end to quickly cover up the GDP-containing subunits

Question 181

The anaphase-promoting complex or cyclosome (APC/C) triggers the onset of anaphase by doing which of the following?

triggering the destruction of the condensins that hold the duplicated chromosomes in a condensed state
phosphorylating the motor proteins that pull the spindle poles apart
triggering the destruction of the cohesins that hold the sister chromatids together
cleaving spindle microtubules

Answer 181

triggering the destruction of the cohesins that hold the sister chromatids together

Question 182

Condensins

are degraded when cells enter M phase.
assemble into complexes on the DNA when phosphorylated by M-Cdk to condense the chromatin into mitotic chromosomes.
are involved in holding sister chromatids together.
bind to DNA before DNA replication begins.

Answer 182

assemble into complexes on the DNA when phosphorylated by M-Cdk to condense the chromatin into mitotic chromosomes.

Question 183

Which of the following statements is TRUE?

The mitotic spindle is largely made of intermediate filaments.
The contractile ring divides the nucleus in two.
The mitotic spindle helps segregate the chromosomes to the two daughter cells.
The contractile ring is made largely of microtubules and actin filaments.

Answer 183

The mitotic spindle helps segregate the chromosomes to the two daughter cells.

Question 184

Which of the following does not occur during M phase in animal cells?

breakdown of nuclear envelope
condensation of chromosomes
growth of the cell
attachment of chromosomes to microtubules

Answer 184

growth of the cell

Question 185

The principal microtubule-organizing center in animal cells is the

cell cortex.
centromere.
kinetochore.
centrosome.

Answer 185

centrosome

Question 186

Mitogens are

extracellular signals that stimulate cell division.
kinases that cause cells to grow in size.
produced by mitotic cells to keep nearby neighboring cells from dividing
transcription factors important for cyclin production.

Answer 186

extracellular signals that stimulate cell division.

Question 187

Which of the following statements about the cell cycle is FALSE?

An unfavorable environment can cause cells to arrest in G1.
A cell has more DNA during G2 than it did in G1.
Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.
The cleavage divisions that occur in an early embryo have short G1 and G2 phases.

Answer 187

Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.

Question 188

Which of the following could cause the cell to prematurely enter anaphase and the sister chromatids to separate?

defect in nuclear envelope breakdown
defect in cohesion removal
defect in dynein motor proteins
defect in the spindle assembly checkpoint

Answer 188

defect in the spindle assembly checkpoint

Question 189

Which of the following structural changes is not typically seen in a cell that is undergoing apoptosis?

The cell develops irregular bulges.
The cytoskeleton collapses.
The cell swells.
The nuclear envelope disassembles.

Answer 189

The cell swells.

Question 190

Which of the following statements about the anaphase-promoting complex (APC) is FALSE?

It is continuously active throughout the cell cycle.
M-Cdk stimulates its activity.
It inhibits M-Cdk activity.
It promotes the degradation of proteins that regulate M phase.

Answer 190

It is continuously active throughout the cell cycle.

Question 191

The contractile ring is composed of
tubulin and kinesin
tubulin and dynein
keratin fibers
actin and myosin

Answer 191

actin and myosin

Question 192

The binding of ATP causes a conformational change in myosin that
moves the myosin head one step forward on the actin filament
moves the actin filament in a force-generating “power stroke”
releases the myosin head from the actin filament
attaches the myosin head to the actin filament

Answer 192

releases the myosin head from the actin filament

Question 193

What is the function of condensins?
to break down the nuclear envelope
to shorten the contractile ring
to hold sister chromatids together
to coil sister chromatids into a compact form

Answer 193

to coil sister chromatids into a compact form

Question 194

Microtubules participate in the spatial polarization of nerve cells because
microtubules have no polarity
microtubules are only located in the nerve cell body
microtubule (-) ends originate near the cell body, allowing (+) end-directed transport along the axon
microtubules extend through the axon with the (-) end towards the terminal and bind vesicles there

Answer 194

microtubule (-) ends originate near the cell body, allowing (+) end-directed transport along the axon

Question 195

Which of the following changes takes place when a skeletal muscle contracts?
Z discs move further apart.
Sarcomeres become shorter.
Myosin filaments contract.
Actin filaments contract.

Answer 195

Sarcomeres become shorter.

Question 196

In the graph below, Peak B would be expected to contain cells that are in which phase(s) of the cell cycle?

(peak has cells with 2 DNA per cell)

G2
G2 and prophase
G1
prophase

Answer 196

G2 and prophase

Question 197

Characteristics of a cell undergoing programmed cell death include all of the following EXCEPT:
cell lysis
breakdown of nuclear lamina
blebbing of large membrane-bound vesicles
a relatively intact membrane

Answer 197

cell lysis

Question 198

When cells enter mitosis, their existing array of cytoplasmic microtubules has to be has to be rapidly broken down and replaced with the mitotic spindle that forms to pull the chromosomes into the daughter cells. The enzyme katanin, named after Japanese samurai swords, is activated during the onset of mitosis and chops microtubules into short pieces. What is the fate of the microtubule fragments created by katanin?

The cleaved microtubule fragments largely lack a GTP-cap so they rapidly depolymerize.
The cleaved microtubule fragments are recognized as a substrate by M-Cdk, which phosphorylates them to target them for destruction.
The cleaved microtubule fragments are stable since they can be used as precursors to synthesize the new mitotic spindle microtubules.
The cleaved microtubule fragments are quickly ubiquitinated and degraded by the proteosome.

Answer 198

The cleaved microtubule fragments largely lack a GTP-cap so they rapidly depolymerize.

Question 199

How are spindle microtubules attached to chromosomes?
The minus ends of the microtubules bind directly to a protein complex on DNA
The plus ends of the microtubule bind directly to DNA
The microtubules bind to cohesin complexes on the DNA
The microtubules bind to the kinetochore complexes through a connecting protein

Answer 199

The microtubules bind to the kinetochore complexes through a connecting protein

Question 200

A key signal for the metaphase to anaphase transition is:
the appropriate amount of time has passed since the initial activation of M-Cdk
p53 phosphorylation
the nuclear lamina has fully disassembled
all chromosomes “feel” tension on their kinetochores

Answer 200

all chromosomes “feel” tension on their kinetochores

Question 201

The figure below shows the pathway leading to M-Cdk (MPF) activation. What is the role of Cdc25 in this pathway?

Cdc25 is a threonine kinase that stimulates M-Cdk (MPF) activation.
Cdc25 is a threonine phosphatase that removes an inhibitory phosphate.
Cdc25 is tyrosine phosphatase that removes an inhibitory phosphate.
Cdc25 is a tyrosine kinase that stimulates M-Cdk (MPF) activation.

Answer 201

Cdc25 is tyrosine phosphatase that removes an inhibitory phosphate.

Question 202

The cytoskeletal system characterized as being comprised of rope-like fibers that give the cell mechanical strength and distribute mechanical stress are:
intermediate filaments
myosin thick filament
actin filaments
microtubules

Answer 202

intermediate filaments

Question 203

Which of the following statements about skeletal muscle contraction is FALSE?
When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane.
During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.
A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament.
The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca into the sarcoplasmic reticulum, triggering a muscle contraction.

Answer 203

The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca into the sarcoplasmic reticulum, triggering a muscle contraction.

Question 204

You are studying nuclear lamins and use recombinant DNA technology to alter the coding sequence of a nuclear lamin gene. The alteration you make creates a situation such that the gene now codes for a nuclear lamin protein that can no longer be phosphorylated when the nuclear envelope is broken down during mitosis. What do you predict would happen if the cell only had the altered nuclear lamin gene (and not the unaltered version)?

Disassembly of the nuclear lamins will occur prematurely because the lamins cannot be phosphorylated.
Nuclear lamins will be unable to produce dimers, as the coiled-coil formation will be disrupted.
Nuclear lamins will no longer disassemble properly during mitosis.
Mitosis should proceed as usual because the dephosphorylation of the lamin is what is important for nuclear lamina assembly during mitosis, so phosphorylation
will not be necessary

Answer 204

Nuclear lamins will no longer disassemble properly during mitosis.

Question 205

Progression through the cell cycle requires a cyclin to bind to a Cdk because
-without cyclin binding, a cell-cycle checkpoint will be activated.
-cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle.
-the cyclins are the molecules with the enzymatic activity in the complex.
-the binding of a cyclin to Cdk is required for Cdk enzymatic activity.

Answer 205

-the binding of a cyclin to Cdk is required for Cdk enzymatic activity.

Question 206

Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2?

The cell would be unable to enter G .2
The cell would enter M phase under conditions when normal cells would not.
The cell would be unable to enter M phase.
The cell would pass through M phase more slowly than normal cells

Answer 206

The cell would enter M phase under conditions when normal cells would not.

Question 207

The G1 DNA damage checkpoint

causes cells to proceed through S phase more quickly.
is activated by errors caused during DNA replication.
involves the inhibition of cyclin–Cdk complexes by p21.
activates APC

Answer 207

involves the inhibition of cyclin–Cdk complexes by p21.

Question 208

Consider the events that lead to the formation of the new nucleus at telophase. How do nuclear and cytosolic proteins become properly re-sorted so that the new nucleus
contains nuclear proteins but not cytosolic proteins?

-Because the nuclear envelope reassembles on the surface of the chromosomes, cytosolic proteins are excluded from the reforming nucleus. Nuclear proteins are selectively imported through the NPC by nuclear transport receptors that recognize the NLS they contain..
-Nuclear proteins bind chromosomes during mitosis. Because the nuclear envelope reassembles on the surface of the chromosomes, nuclear proteins end up inside the nucleus and cytoplasmic proteins end up on the outside of the nuclear envelope.
-Proteins are degraded during mitosis, so cytoplasmic and nuclear proteins are targeted via their normal targeting mechanisms.
-Cytosolic proteins are excluded from the reforming nucleus due to their cytoplasmic signal
recognition sequence. Nuclear proteins are selectively imported through the NPC due to their
nuclear localization sequence..

Answer 208

Because the nuclear envelope reassembles on the surface of the chromosomes, cytosolic proteins are excluded from the reforming nucleus. Nuclear proteins are selectively imported through the NPC by nuclear transport receptors that recognize the NLS they contain..

Question 209

All of the following is true EXCEPT:

Apoptosis is mediated by special intracellular proteases, one of which cleaves nuclear lamins.
Cells do not pass directly from G1 to M unless there are sufficient nutrients to complete an entire cell cycle.
The enzymatic activity of a Cdk protein is determined both by the presence of a bound cyclin and by the phosphorylation state of the Cdk.
Developing neurons compete for limited amounts of survival factors.

Answer 209

Cells do not pass directly from G1 to M unless there are sufficient nutrients to complete an entire cell cycle.

Question 210

What is a reasonable explanation for why cells have evolved a special G0 phase to exit from the cell cycle, rather than just stopping in G1 and not moving on to S phase?

-Because it takes too much energy to keep synthesizing G1 cyclins when they are not needed.
-Because the G1 state leaves the cell in a vulnerable state since it has not yet duplicated its genome and thus is more sensitive to radiation damage.
-The G0 state offers protection from aberrant a tivation of cell division because the cell-cycle control system is largely dismantled.
-Because the G0 state is more stable since the dynamic instability of microtubules is paused
since spindles are not needed anymore

Answer 210

-The G0 state offers protection from aberrant a tivation of cell division because the cell-cycle control system is largely dismantled.

Question 211

Cyclins are targeted for destruction in a cell-cycle-dependent manner by:

ubiquitination
phagocytosis
phosphorylation
G-protein binding

Answer 211

ubiquitination