Exam 2 Weekly Quizzes Material Flashcards
Why do membrane lipids form bilayers in water?
A. The hydrophilic tail shuns water and the hydrophobic head is attracted to water.
B. The hydrophilic head shuns water and the hydrophobic tail is attracted to water.
C. The hydrophobic head shuns water and the hydrophilic tail is attracted to water.
D. The hydrophobic tail shuns water and the hydrophilic head is attracted to water.
D
We can estimate the relative mobility of a population of molecules in a cell membrane by fluorescently labeling the molecules of interest, bleaching the label in one small area, and then measuring the speed of signal recovery as the molecules migrate back into the bleached area. What is this method called?
FRAP
A bacterial cell is suddenly expelled from a warm human intestine into the cold world outside. Which one of the following adjustments might the cell make to maintain the same level of membrane fluidity?
Increase the amount of cholesterol in its membrane
Produce lipids with shorter hydrocarbon tails and more double bonds
Produce lipids with longer hydrocarbon tails and fewer double bonds
Produce lipids with shorter hydrocarbon tails and fewer double bonds
Decrease the amount of glycolipids in its membrane
Produce lipids with shorter hydrocarbon tails and more double bonds
Which of the following components are present in cholesterol?
A. a sterol polar head group and two short hydrocarbon tails
B. two short hydrocarbon tails
C. a sterol polar head group
D. a sterol polar head group and one short hydrocarbon tail
E. one short hydrocarbon tail
D
Which of the following statements about the movement of lipids in the bilayer is TRUE?
A. Lipids are free to move AND rotate within one plane of a bilayer
B. Lipids are free to move AND rotate within one plane of a bilayer, and also spontaneously flip from one plane to the other of a bilayer
C. Lipids are free to rotate within one plane of a bilayer
D.Lipids are free to move within one plane of a bilayer.
E. Lipids spontaneously flip from one plane to the other of a bilayer
A
Which one of the following is NOT a typical function for a membrane protein?
A.To generate energy so lipid-soluble material can diffuse through the membrane
B. To transport specific molecules across a permeability barrier
C. To function as enzymes to catalyze specific reactions near the cell surface
D. To receive signals from neighboring cells or the extracellular environment
E. To stabilize the cell membrane by attachment to the extracellular matrix or cell cortex
A
Which of the following is NOT an integral membrane protein?
A transmembrane protein that spans the lipid bilayer as an alpha-helix
A lipid-linked protein anchored to the outer leaflet of the membrane
A monolayer-associated protein tucked into the inner leaflet of the lipid bilayer
A transmembrane protein that spans the lipid bilayer as a beta-barrel
A protein attached to the membrane by non-covalent interactions with other membrane proteins
A protein attached to the membrane by non-covalent interactions with other membrane proteins
Membrane proteins can be extremely mobile within the lipid bilayer, but sometimes a cell needs to restrict membrane protein mobility. Which one of the following mechanisms is NOT typically used?
Anchoring a membrane protein to the cell cortex
Forming tight junctions between cells to limit proteins to the apical or basal-lateral domains
Forming hydrophobic interactions with the hydrocarbon tails in lipid bilayer
Tethering a membrane protein in one cell to a membrane protein in another cell
Anchoring a membrane protein to the extracellular matrix
Forming hydrophobic interactions with the hydrocarbon tails in lipid bilayer
The red blood cell has been an important model for the study of cell membranes, in particular for the study of how the cell cortex can provide structural support for the cell membrane. Which one of the following proteins is the major fibrous protein in the red blood cell cortex?
Spectrin
Which one of the following statements about membrane carbohydrates is FALSE?
They help absorb water and create a slimy surface
All of the statements are correct
Most are composed of short or long chains of sugars called oligosaccharides (or polysaccharides).
They are typically found on the extracellular surface of a membrane
They play an important role in cell-cell recognition
All correct
Transporters, in contrast to channels, work by _____________________.
a gating mechanism
filtering solutes by charge
filtering solutes by size
specific binding to solutes
D
Which one of the following statements about passive and/or active transport is FALSE?
The movement of an ion against it electrochemical gradient is a form of active transport.
The transport of glucose across the membrane can be active or passive, depending on the nature of the transporter.
Coupled transporters use electrochemical gradients to drive active transport of other solutes.
ATP driven pumps move solutes down their concentration gradients.
ATP driven pumps move solutes down their concentration gradients.
Active transport requires the input of energy 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?
Light-driven
K+-coupled
ATP-driven
Na+-coupled
K+-coupled
The Na+-K+ pump in the plasma membrane uses the energy from ATP hydrolysis to pump the two ions against their electrochemical gradients. In what directions are the ions pumped across the membrane?
Na out and K in
Which organelle is most important for controlling the concentration of calcium ions in the cytosol using the Ca2+ ATPase pump?
ER
Which of the following statements best describes the behavior of a gated ion channel?
It remains closed if unstimulated.
It opens more widely as the stimulus becomes stronger.
It opens more frequently in response to a stimulus.
It stays open continuously when stimulated.
It opens more frequently in response to a stimulus.
When voltage-gated Na+ channels are stimulated in a nerve cell, what happens to the membrane potential?
Less negative
Which one of the following is specifically required for the secretion of neurotransmitters in response to an action potential?
The opening of voltage-gated Ca2+ channels
During an action potential, which of the following helps return the membrane potential to its resting potential?
Opening of VG K channels
Both excitatory and inhibitory neurons can form synapses with their target cells. How do inhibitory neurotransmitters prevent the post-synaptic cell from firing another action potential?
By opening Cl channels
Proteins have to be unfolded during their transport across the membranes of all but one of the following organelles. Which one?
Nucleus
What is the role of the nuclear localization sequence (NLS) in a nuclear protein?
A. It prevents the protein from diffusing out of the nucleus through nuclear pores.
B. It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.
C. It is a hydrophobic sequence that enables the protein to enter the nuclear membranes.
D. It aids in protein unfolding so that the protein can thread through nuclear pores.
E. It interacts with DNA to anchor the protein in the nucleus.
B
Which of the following statements about mitochondrial proteins that are synthesized in the cytosol is FALSE?
The proteins are transported across the mitochondrial membranes while being synthesized.
The proteins cross both the inner and outer mitochondrial membranes as they are imported.
Chaperone proteins help draw the proteins inside the mitochondrion.
The proteins are unfolded as they are transported into the mitochondria.
The proteins usually have a signal sequence at their N-terminus.
The proteins are transported across the mitochondrial membranes while being synthesized.
Which of the following choices reflects the appropriate order through which a protein destined for the plasma membrane travels?
ER -> Golgi apparatus -> plasma membrane
After isolating the rough endoplasmic reticulum (ER) from the rest of the cytoplasm, you purify the RNAs attached to it. Which of the following proteins do you NOT expect the RNA from the rough ER to encode?
ER membrane proteins
mitochondrial proteins
plasma membrane proteins
soluble secreted proteins
lysosomal proteins
mitochondrial proteins
Most proteins destined to enter the endoplasmic reticulum ______________________
are transported across the membrane after their synthesis is complete.
begin to cross the membrane while still being synthesized.
are synthesized on free ribosomes in the cytosol.
contain a C-terminal signal sequence that binds to SRP.
remain within the endoplasmic reticulum.
begin to cross the membrane while still being synthesized.
Which of the following statements about secretion is TRUE?
A. Proteins destined for constitutive exocytosis aggregate as a result of the acidic pH of the trans Golgi network.
B. The signal sequences of proteins destined for constitutive exocytosis guide their packaging into the correct vesicles.
C. The phosphorylated sugar mannose 6-phosphate acts as a tag on proteins destined for constitutive exocytosis to ensure their packaging into the correct vesicles.
D. The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell’s exterior.
E. Vesicles for regulated exocytosis will not bud off the trans Golgi network until the appropriate signal has been received from the cell.
D The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell’s exterior.
An individual transport vesicle ______________________
will fuse with only one type of membrane.
is enclosed by a membrane with the same lipid and protein composition as the membrane of the donor organelle.
contains only one type of protein in its lumen.
usually travels toward the plasma membrane if it is endocytic.
A. will fuse with only one type of membrane.
Which organelle sorts ingested molecules and recycles some of them back to the plasma membrane?
endosome
What protein can assemble into a basket-like network that gives budding vesicles their shape?
Clathrin
measures the overall mobility of a molecule by the time it takes to recover
FRAP
measures the mobility of the molecule based on distance traveled
SPT
A larger molecule has the __ mobility and __ recovery time
least; longest recovery time
Where is the signal recognition particle located
cytosol
where is protein translocator located
ER membrane
where is mRNA located
cytosol
where is SRP receptor located
ER membrane
where is the active site of signal peptidase located
er lumen
Your friend has just joined a lab that studies vesicle budding from the Golgi and has been given a cell line that does not form mature vesicles. He wants to start designing some experiments but was not listening carefully when he was told about the molecular defect of this cell line. He is too embarrassed to ask and comes to you for help. He does recall that this cell line forms coated pits but vesicle budding and the removal of coat proteins don’t happen.
Which of the following proteins might be lacking in this cell line?
Dynamin
process that activates the absorption of fluid and molecules through vesicles and clathrin coated pits
pinocytosis
process that activates the ingestions of sizable particles. It’s mainly carried out specific phagocytic cells
phagocytosis
process that brings back unoccupied receptors to the plasma membrane from endosomes
transcytosis
process by which demeaning obsolete parts of the cell is done
autophagy
Indicate whether each of the following would increase or decrease the effect of acetylcholine.
A. addition of a drug that stimulates the GTPase activity of the Gα subunit
B. mutations in the K+ channel that keep it closed all the time
C. modification of the Gα subunit by cholera toxin
D. a mutation that decreases the affinity of the βγ complex of the G protein for the K+ channel
decrease
decrease
increase (toxin inhibits Gtp hydrolysus)
decrease
You are interested in how cyclic-AMP-dependent protein kinase A (PKA) functions to affect learning and memory, and you decide to study its function in the brain. It is known that, in the cells you are studying, PKA works via a signal transduction pathway like the one depicted in the figure below. Furthermore, it is also known that activated PKA phosphorylates the transcriptional regulator called Nerd that then activates transcription of the gene Brainy. Which situation described below will lead to an increase in Brainy transcription? Explain your answer.
A. a mutation in the Nerd gene that produces a protein that cannot be phosphorylated by PKA
B. a mutation in the nuclear import sequence of PKA from PPKKKRKV to PPAAAAAV
C. a mutation in the gene that encodes cAMP phosphodiesterase that makes the enzyme inactive
D. a mutation in the gene that encodes adenylyl cyclase that renders the enzyme unable to interact with the α subunit of the G protein
C; cAMP phosdiesterase converts cAMP to AMP which terminates signal (transcription never terminating)
Most members of the steroid hormone receptor family __________________.
do not undergo conformational changes
are cell-surface receptors
interact with signal molecules that diffuse through the plasma membrane
are found only in the endoplasmic reticulum
interact with signal molecules that diffuse through the plasma membrane
The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________.
activating an intracellular protein kinase
activating a receptor tyrosine kinase
diffusing into cells and stimulating guanylyl cyclase directly
activating a G-protein
diffusing into cells and stimulating guanylyl cyclase directly
Which one of the following statements is TRUE?
Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor.
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 will always induce the same response as that is produced by the signal molecule.
A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response.
Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor.
Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which one of the following statements is FALSE?
Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways.
Heart muscle cells, salivary gland cells, and skeletal muscle cells all express the same acetylcholine receptor.
Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.
Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract.
Heart muscle cells, salivary gland cells, and skeletal muscle cells all express the same acetylcholine receptor.
The growth factor Superchick stimulates the growth of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase (RTK). Many tumor cell lines have mutations in the gene that encodes this receptor. Which one of the following mutations would be expected to promote uncontrolled (or, in other words, hyperactive) cell growth?
a mutation that destroys the kinase activity of the receptor
a mutation that prevents the binding of the normal extracellular signal to the receptor
a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor
a mutation that prevents dimerization of the receptor
a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor
Which one of the following usually happens when a cell-surface receptor activates a heterotrimeric G protein?
The inactive α subunit exchanges its bound GDP for GTP and becomes activated.
It activates the α subunit and inactivates the βγ complex.
The β subunit exchanges its bound GDP for GTP.
The GDP bound to the β subunit is phosphorylated to form bound GTP.
The inactive α subunit exchanges its bound GDP for GTP and becomes activated.
When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________.
hormone
Which one of the following statements is TRUE?
Ras is a heterotrimeric G-protein.
Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP.
MAP kinase kinase phosphorylates MAP kinase.
Some RTKs stimulate phospholipase C to phosphorylate an inositol phosholipid in the plasma membrane.
MAP kinase kinase phosphorylates MAP kinase.
The length of time a G protein will signal is determined by _____________.
the activity of kinases that turn GTP into GDP.
the ability of the G protein to phosphorylate itself.
the degradation of the G protein after Gα separates from Gβγ
the GTPase activity of Gα
the GTPase activity of Gα
Which of the following processes involve the combining of a message from one signaling molecule with that of another to either enhance or inhibit a cellular effect?
Signal reception
Signal integration
Signal amplification
Signal elimination
Integration
