Exam 2 Weekly Quizzes Material

Question 1

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.

Answer 1

D

Question 2

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?

Answer 2

FRAP

Question 3

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

Answer 3

Produce lipids with shorter hydrocarbon tails and more double bonds

Question 4

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

Answer 4

D

Question 5

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

Answer 5

A

Question 6

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

Answer 6

A

Question 7

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

Answer 7

A protein attached to the membrane by non-covalent interactions with other membrane proteins

Question 8

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

Answer 8

Forming hydrophobic interactions with the hydrocarbon tails in lipid bilayer

Question 9

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?

Answer 9

Spectrin

Question 10

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

Answer 10

All correct

Question 11

Transporters, in contrast to channels, work by _____________________.
a gating mechanism
filtering solutes by charge
filtering solutes by size
specific binding to solutes

Answer 11

D

Question 12

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.

Answer 12

ATP driven pumps move solutes down their concentration gradients.

Question 13

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

Answer 13

K+-coupled

Question 14

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?

Answer 14

Na out and K in

Question 15

Which organelle is most important for controlling the concentration of calcium ions in the cytosol using the Ca2+ ATPase pump?

Answer 15

ER

Question 16

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.

Answer 16

It opens more frequently in response to a stimulus.

Question 17

When voltage-gated Na+ channels are stimulated in a nerve cell, what happens to the membrane potential?

Answer 17

Less negative

Question 18

Which one of the following is specifically required for the secretion of neurotransmitters in response to an action potential?

Answer 18

The opening of voltage-gated Ca2+ channels

Question 19

During an action potential, which of the following helps return the membrane potential to its resting potential?

Answer 19

Opening of VG K channels

Question 20

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?

Answer 20

By opening Cl channels

Question 21

Proteins have to be unfolded during their transport across the membranes of all but one of the following organelles. Which one?

Answer 21

Nucleus

Question 22

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.

Answer 22

B

Question 23

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.

Answer 23

The proteins are transported across the mitochondrial membranes while being synthesized.

Question 24

Which of the following choices reflects the appropriate order through which a protein destined for the plasma membrane travels?

Answer 24

ER -> Golgi apparatus -> plasma membrane

Question 25

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

Answer 25

mitochondrial proteins

Question 26

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.

Answer 26

begin to cross the membrane while still being synthesized.

Question 27

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.

Answer 27

D The membrane of a secretory vesicle will fuse with the plasma membrane when it discharges its contents to the cell’s exterior.

Question 28

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.

Answer 28

A. will fuse with only one type of membrane.

Question 29

Which organelle sorts ingested molecules and recycles some of them back to the plasma membrane?

Answer 29

endosome

Question 30

What protein can assemble into a basket-like network that gives budding vesicles their shape?

Answer 30

Clathrin

Question 31

measures the overall mobility of a molecule by the time it takes to recover

Answer 31

FRAP

Question 32

measures the mobility of the molecule based on distance traveled

Answer 32

SPT

Question 33

A larger molecule has the __ mobility and __ recovery time

Answer 33

least; longest recovery time

Question 34

Where is the signal recognition particle located

Answer 34

cytosol

Question 35

where is protein translocator located

Answer 35

ER membrane

Question 36

where is mRNA located

Answer 36

cytosol

Question 37

where is SRP receptor located

Answer 37

ER membrane

Question 38

where is the active site of signal peptidase located

Answer 38

er lumen

Question 39

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?

Answer 39

Dynamin

Question 40

process that activates the absorption of fluid and molecules through vesicles and clathrin coated pits

Answer 40

pinocytosis

Question 41

process that activates the ingestions of sizable particles. It’s mainly carried out specific phagocytic cells

Answer 41

phagocytosis

Question 42

process that brings back unoccupied receptors to the plasma membrane from endosomes

Answer 42

transcytosis

Question 43

process by which demeaning obsolete parts of the cell is done

Answer 43

autophagy

Question 44

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

Answer 44

decrease
decrease
increase (toxin inhibits Gtp hydrolysus)
decrease

Question 45

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

Answer 45

C; cAMP phosdiesterase converts cAMP to AMP which terminates signal (transcription never terminating)

Question 46

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

Answer 46

interact with signal molecules that diffuse through the plasma membrane

Question 47

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

Answer 47

diffusing into cells and stimulating guanylyl cyclase directly

Question 48

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.

Answer 48

Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor.

Question 49

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.

Answer 49

Heart muscle cells, salivary gland cells, and skeletal muscle cells all express the same acetylcholine receptor.

Question 50

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

Answer 50

a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor

Question 51

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.

Answer 51

The inactive α subunit exchanges its bound GDP for GTP and becomes activated.

Question 52

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________.

Answer 52

hormone

Question 53

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.

Answer 53

MAP kinase kinase phosphorylates MAP kinase.

Question 54

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

Answer 54

the GTPase activity of Gα

Question 55

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

Answer 55

Integration