BIO 320 Cell Biology Exam II Answers
I. Multiple Choice (2 points each, 50 points total)
1. With regard to the permeability of the membrane, which of the following is NOT true?
A. Compounds having a high molecular weight or those that are charged would have a low permeability coefficient
B. The leveling off of the rate of transport with increasing substrate concentration shows that there is a binding step in facilitated transport.
C. The rate of simple diffusion depends on the ability of a compound to dissolve in the membrane
D. The permeability coefficient describes the ?G or direction of transport
2. With respect to the membrane potential which of the following is NOT true?
A. The greater amount of potassium inside relative to outside, the more negative the membrane potential will be.
B. In a resting neuron, sodium and potassium contribute equally to the membrane potential
C. An ion gradient contributes to the membrane potential in proportion to its membrane permeability
D. The Goldman equation can be used to predict the resting membrane potential of cells.
3. With respect to transport ATPases which of the following is NOT true?
A. The sodium/potassium ATPase is only needed to generate an electrical potential
B. In P type ion transport ATPases, phosphorylation and dephosphorylations is associated with a change in affinity for the ion.
C. The C subunits of the F1/Fo ATPase rotate due to the flow of H+ ions from outside the mitochondria to the inner space (matrix) of the mitochondria.
D. The multidrug resistance transporter binds and hydrolyzes 2 ATP per pumping cycle
4. Which is NOT a component of the permeability coefficient?
A. The partition coefficient
B. The size of the molecule
C. The thickness of the membrane
D. The concentration gradien
5. With respect to channels and ion currents which is NOT true?
A. Chanels can be gated open, gated closed or inactivated.
B. The voltage sensor of a sodium channel is the S6 alpha helix
C. Single channel ion currents are all or none
D. Channel current depends only on the gradient of the ion transported
6. During the undershoot of the action potential, which IS true?
A. During the relative refractory period, the threshold potential will be signifcantly more positive than it is at rest.
B. The undershoot arises because during this period the cell is more permeable to sodium relative to potassium than it is at rest.
C. During the first part of the undershoot, potassium channels are inactivated
D. Recovery from the negative potential of the undershoot depends on the Sodium Potassium ATPase.
7. Src was used as a protein to report the effect of stretch on signaling through adhesions. How was this done?
A. The serine phosphorylation of Src was shown to increase with stretch
B. FRET between the the terminal portions of Src containing two different fluorescent protein was shown to change.
C. Src was shown to become tyrosine phosphorylated upon stretch
D. Signaling through Src was not affected by stretch
8. With respect to voltage-gated Na+/K+ channels which IS true?
A. For both sodium and potassium channels, 4 domains of the channel protein come together to make the channel pore
B. Water bound to ions must be removed from the ion before it goes through the channel
C. The alpha helices composing the channel are responsible for both gating and inactivation
D. Channel selectivity does not involve binding to the ion
9. In neurons, which of the following IS true?
A. The highest density of sodium channels are at the dentrites
B. Excitatory neurotransmitters open chloride or potassium channels.
C. Depolarization over dendrites and the soma or cell body is conducted by passive spread.
D. Speeding up conduction in mammals is mainly accomplished by making the axon diameter larger
10. In epithelial cells, which IS true of transport of glucose?
A. A glucose indirect active transporter pumps glucose out on the apical side
B. Tight junctions prevent leakage of glucose through the space between the cells
C. A facilitated diffusion transporter lets glucose in on the basal side
D. It does not matter where the glucose transporters are located in the epithelial cells
11. When signaling through G protein coupled receptors, which of the following IS true?
A. Tyrosines on the receptor will typically get phosphorylated
B. A G alpha subunit will switch from GTP to GDP forms in order to signal downstream
C. Switch domains on the G alpha subunit will be exposed due to dissociation of the ?? subunits
D. The alpha subunit must bind to the beta-gamma subunits in order to hydrolyze GTP
12. Which of the following WOULD be expected when PDGF binds to PDGF receptors (Receptor Tyrosine Kinase type)?
A. A change in conformation takes place on the cytoplasmic portion of the receptor
B. Receptors cross phosphorylate each other on serine residues
C. Other proteins would be recruited to bind to the receptor by their SH2 domains
D. A large heterotrimeric G protein is activated.
13. Which is NOT an example of the ways receptors are downregulated?
A. Signaling downstream is prevented as in the case of binding arrestin
B. Receptors are internalized and stored
C. Receptor affinity is changed so that it does not bind hormone
D. Proteases in the plasma membrane degrade the receptor
14. In signaling through receptor tyrosine kinases, what is the specific role of SOS?
A. It binds to and activates MEK
B. It acts as a GEF for Ras.
C. It causes MAP kinase to move into the nucleus
D. It recruits GRB2 to the receptor
15. Which of the following would be unlikely candidate for being a protooncogene?
A. A mutated constitutively active Ras
B. A mutated constitutively active PTEN
C. A mutated and constitutively active Raf
D. A mutated and constitutively active MAP kinase
16. Which of the following is NOT an action of calcium we have seen
A. Activation of synaptotagmin in nerve terminals
B. Smooth muscle contraction
C. G protein activation
D. The calcium dependent phosphorylation of CREB by CAM kinase.
17. Which of the following about cyclic AMP (cAMP) is NOT ture?
A. Has the same effect in every cell.
B. Normally activates PKA
C. Can increase due to activity of adenylyl cyclase
D. Has similar effects in smooth muscle to that of cGMP
18. Which is NOT related to blocking apoptosis due to RTK signaling
B. PI-3 Kinase
19. Which is the correct sequence of the ras pathway
A. Ras => SOS=>Raf=>MEK=>MAP kinase=>Jun
B. SOS => Ras=>Raf=>MEK=>MAP kinase=>Jun
C. SOS => Raf=>Ras=>MEK=>MAP kinase=>Jun
D. SOS => Ras=>MEK=>Raf=>MAP kinase=>Jun
20. Which IS a difference between cAMP and cGMP?
A. Their effects on smooth muscle
B. Second messengers
C. Their concentration is reduced by phosphodiesterases
D. Signaling pathways for their formation
21. Focal contacts represent regions in the cell where all are true except
A. Clustered integrins link to actin filaments
B. Actin filaments bind and are under tension
C. Signaling occurs that relates to cell growth and survival
D. Clustered integrins bind to intermediate filaments forming hemidesmosomes.
22. Which is NOT true concerning conduction
A. Propagation is faster than passive spread of depolarization
B. Potassium ions carry the depolarization along the inside of the membrane
C. Conduction is sped up by myelination which reduces capacitance
D. Passive spread is limited to short distances because potassium is permeable
23. In tryosine kinase receptors which IS true
A. Mutation of a single receptor gene is typically enough to cause cancer
B. The receptor can activate via via phosphorylation of its own tyrosines or by being phosphorylated by a neighboring (dimerized) receptor
C. The most dangerous and difficult to deal with mutation in the signaling pathway would be one that results in a constitutively active receptor.
D. Multiple signaling pathways are initiated from a single receptor.
24, In secretion at the nerve terminal, which is NOT true
A. Vesicles are bound to the target membrane by SNARES
B. NSF forces the vesicle to fuse with the target membrane
C. Secretion is regulated by calcium
D. The last step in the fusion of secretory vesicles depends on synaptotagmin
25. In terms of the action of pumps which is NOT correct regarding ion gradients in the cell
A. The inside of the mitochondria is acidic relative to the cyoplasm
B. The lysosomes are acidic relative to the cytoplasm
C. The inside of the cell has high potassium compared to the outside of the cell
D. The endoplasmic reticulum contains high levels of calcium relative to the cytosol
26. Matching (1 point each, 7 points total)
1. Organelle that makes ATP ________
2. Organelle that adds mannose-6-P to proteins ________
3. Organelle that serves as an internal calcium store ______
4. Organelle starts out as a clathrin coated vesicle _______
5. Organelle that makes ribosomes ________
6. Organelle that uses Ran to drive active transport ________
7. Organelle that makes proteins using an RNA template ________
E. Endoplasmic reticulum
II. TRUE/ FALSE (1 points each, 10 points total)
27. The chloride concentration inside versus outside of the cell is the reciprocal of the sodium concentration
28. Virtually all cells have lipid rafts but only some cells have cavelolae
29. The multidrug resistance transporter is an ABC (or ATP cassette) transporter that pumps foreign compounds outside the cell
30. The Nernst equation gives the maximum potential that could develop due to a single given ion gradient.
31. Ras requires a GEF to hydrolyze GTP
32. Integrins can signal for cell survival by activating PI-3 Kinase
33. The relationship between receptor occupation and the signaling response is always equal – 50% receptor occupation gives a 50% of maximal signaling response.
34. Downregulation of beta-adrenergic receptors occurs when the receptor is phosphorylated and binds arrestin.
35. SH2 domains bind to polyproline whereas SH3 domains bind to tyrosine phosphate
36. The absolute refractory period is due to opening of voltage gated potassium channels
III. Short Answers (22 points)
37. Give two different ways that phosphatidyl inositol lipids are used in signaling. (4 points)
38. Explain the role of VAMP, Syntaxin, and Synaptotagmin in nerve cell function (4 points)
39. Based on the Nernst equation, membrane potential will change by
40. Explain in terms of channel opening/closing and ion movements what is going on at the labeled points in the diagram of an action potential below. (10 points)
IV. Discussion Questions (Total 11 points)
41. Give a rationale for why RTKs activate several parallel signaling pathways. Include in your answer how each of the three main pathways we learned about contribute to a growth signal (5 points)
42. Explain how alpha and beta receptors have opposite effects on smooth muscle. Explain in terms of G protein second messengers and target effects (6 points)
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