BIOL 314 Final Flashcards by Charlotte Barnes

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.

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

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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

left-handedness

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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

hydrophobic

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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

ribbon

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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

hydrogen bonds

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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

hydrogen bonds along or between strands of the protein backbone

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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.

sequence

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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

inside a cavity on the protein surface

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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

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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.

amino acid sequence

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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

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

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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.

water molecule

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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.

Proteins are tethered to the extracellular matrix.

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

phospholipids
sterols
triacylglycerides
glycolipids

phospholipids

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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.

They are made primarily of α helices.

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

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

cytosolic; endoplasmic reticulum

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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.

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

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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.

The membrane reseals

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

sucrose
ethanol
high salt solution
detergent

detergent

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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

membrane thickness

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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.

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

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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

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

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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.

A few channels remain closed and most open completely

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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

export of glucose out of gut epithelial cells

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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

the concentration of water on either side of the membrane

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+.

depolarized.

Transporters, in contrast to channels, work by filtering solutes by size. specific recognition of transport substrates. filtering solutes by charge. a gating mechanism.

specific recognition of transport substrates.

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+)

Cl- (Na+)

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-

Cl-

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.

active transport

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

C (repolarization phase \)

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

K+-coupled

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.

The entropy in the environment increases as cells grow.

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

surface complementarity between molecules

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

ATP

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

hydrolase

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

translation of protein components

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.

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

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.

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

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.

They form protein aggregates.

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.

Membrane lipids diffuse laterally within the plane of the membrane.

Which of the following functions of the plasma membrane is possible without membrane proteins? intercellular communication import/export of molecules cellular movement selective permeability

selective permeability

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.

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

Which of the following membrane lipids does not contain a fatty acid tail? phosphatidylserine a glycolipid cholesterol phosphatidylcholine

cholestrol

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.

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

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+

Na+

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+.

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

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.

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.

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

estrogen > propanol > alanine > sodium

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

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

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

hydrophobic

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

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

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

-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

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

Mobility of a protein within the cell

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

flippases

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

unsaturated hydrocarbons

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

Membrane lipids diffuse within the plane of the membrane.

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

moving between lipid bilayers

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.

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.

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

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

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

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

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

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

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

an aquaporin

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.

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

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

mitochondria

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

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

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

The protein could slip back out of the mitochondria during transport

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

transport vesicles

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.

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

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.

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

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

ER → Golgi → plasma membrane

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

Proteins imported into the nucleus.

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

docking of the vesicle to the target organelle

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

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

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.

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

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

In the ER lumen

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.

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.

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

the nuclear localization sequence

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.

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.

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

chaperone

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.

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

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

trimeric GTP-binding proteins

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

GTPase activity

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

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

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

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

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

phosphotyrosine

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

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

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

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

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

endocrine

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

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

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

enzyme-coupled receptors

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.

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

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.

hormone.

(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

Notch

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.

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

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

contact-dependent

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.

interact with signal molecules that diffuse through the plasma membrane.

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.

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

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

a mutation that prevents RGFR from binding to RGF

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

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

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

adenylyl cyclase

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

It blocks the enzyme that degrades cyclic GMP

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

one that involves a change in gene expression

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.

The α subunit exchanges its bound GDP for GTP.

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.

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 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

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

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

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

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

adaptins

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.

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

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

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

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

Block the receptor with an antibody

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

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

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.

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

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

Generally used to engulf large targets like microorganisms and cell debris

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.

Transport through an aquaporin beta barrel

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

cAMP

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

To inactivate an activated G protein

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

Binding of GTP

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

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

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

cAMP

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.

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

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.

diffusing into cells and stimulating the cyclase directly.

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

Na+

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

sorting of endocytosed material

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.

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

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

transcytosis

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.

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

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

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

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.

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

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

Specificity of cargo is determined by clathrin binding

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

cis Golgi network.

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.

cytosol

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

uptake of glucose from the intestinal lumen

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

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

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

Phosphorylation of a protein will always result in its activation

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

Bind a guanine nucleotide in their alpha subunit

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

phosphorylated inositol phospholipid

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.

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

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

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.

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

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

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

actin filaments

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

ATP

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

corneal damage caused by cell rupture from mechanical trauma

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

blockage of the Ca2+ pump

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

dynein

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.

Disruption of the polarity of the final desmin strands.

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.

decreasing the binding strength between subunits on filaments.

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.

Cofilin binds to older actin filaments.

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.

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

Which of the following structures shorten during muscle contraction? myosin filaments sarcomeres actin filaments flagella

sarcomeres

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.

The microtubule depolymerizes.

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

none of these

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.

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

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.

Their activities increase at different stages of the cycle.

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.

cyclin levels change during the cycle.

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.

Kinetochores assemble onto chromosomes during late prophase.

At the end of DNA replication, the sister chromatids are held together by the kinetochores. securins. histones. cohesins.

cohesins

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.

The nuclear envelope breaks down.

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.

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

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

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.

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

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.

Paclitaxel promotes apoptosis of the cancer cell.

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

cyclins

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.

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

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.

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

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.

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

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

transcription; proteolysis

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

separase; securin

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.

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

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.

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.

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.

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

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

M phase - cytokinesis

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

mesh

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

prometaphase

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.

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

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

chaperones guide cyclins to the proteosome for degradation

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

sarcoplasmic reticulum

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

microtubules

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.

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.

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.

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

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.

often move in opposite directions to each other.

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

Covalent bonds between protein monomers hold together the cytoskeletal filaments.

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.

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

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.

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

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

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

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.

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

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.

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

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

growth of the cell

The principal microtubule-organizing center in animal cells is the cell cortex. centromere. kinetochore. centrosome.

centrosome

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.

extracellular signals that stimulate cell division.

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.

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

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

defect in the spindle assembly checkpoint

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.

The cell swells.

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.

It is continuously active throughout the cell cycle.

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

actin and myosin

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

releases the myosin head from the actin filament

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

to coil sister chromatids into a compact form

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

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

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.

Sarcomeres become shorter.

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

G2 and prophase

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

cell lysis

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.

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

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

The microtubules bind to the kinetochore complexes through a connecting protein

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

all chromosomes "feel" tension on their kinetochores

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.

Cdc25 is tyrosine phosphatase that removes an inhibitory phosphate.

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

intermediate filaments

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.

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.

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

Nuclear lamins will no longer disassemble properly during mitosis.

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.

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

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

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

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

involves the inhibition of cyclin–Cdk complexes by p21.

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..

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..

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.

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

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

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

Cyclins are targeted for destruction in a cell-cycle-dependent manner by: ubiquitination phagocytosis phosphorylation G-protein binding

ubiquitination