BSCI 230 Exam 2 Questions and Problems - Prof. Reid S. Compton, Exams of Cell Biology

Download BSCI 230 Exam 2 Questions and Problems - Prof. Reid S. Compton and more Exams Cell Biology in PDF only on Docsity! Compton, BSCI 230 Exam 2; 6/26/00 Print Your Name Your Laboratory Section Time: Directions: 1. Print your name on every page of this exam NOW. 2. Use a PEN to complete this exam or you will not be eligible for a regrade. 3. Check to see that you have 7 pages. If you don't, raise your hand. 4. You must confine your answers to the spaces provided. 5. Read the questions carefully! - Be as specific and as concise as you can with your answers. 6. You must hand in your exam by 12:50 PM. Good Luck. Scoring: Page 2 \ourPts. Possible Pts. 16 Page 3 Page 4 Page 5 Page 6 Page 7 19 25 18 14 8 TOTAL Place the letter that identifies the single best answer to the question blow in the blank. (2 pts/ question) .At rest, all of the following are closed EXCEPT: A) Voltage-gated Na+ channels B) Voltage-gated K+ channels C) Delayed K7 channels D) Non-voltage-gated K+ channels _During an action potential, which of the following is primarily responsible for bringing the membrane potential down toward die resting level from the peak? A) Influx of Na+ B) Influx of K+ C) Efflux of Na+ D) Efflux of K+ _The timed closing of voltage-gated Na+ channels after about 1 msec is essential for A) The directional movement of the action potential B) The efflux of K+ C) Preventing the efflux of Na+ D) Membrane depolarization _Movement of Na+ through open voltage-gated Na* channels is driven by A) The Na+ concentration gradient across the membrane B) The membrane potential at rest C) The Na+ concentration across the membrane and the membrane potential at rest D) The Na+ concentration gradient across the membrane and the membrane potential at the peak of the action potential _Open and closing of voltage-gated Na+ channels A) Is triggered by an influx of K+ B) Involves changes in protein conformation C) Depends on whether other ions "plug" the channel D) Is independent of membrane potential ?_The Na+/K+ ATPase causes which of the following to happen? A) Na4 moved to the outside and K+ moved to the inside B) Na+ moved to the inside and K+ moved to the outside C) Na" moved to the outside and 1C moved to the outside D) Na4 moved to the inside and K+ moved to the inside _Nerve and muscle cells, unlike other body cells, are excitable i.e., their membrane voltage can change instantly in response to the correct stimulus. When this happens, all of the following correctly apply at the cellular level EXCEPT: A) Voltage-gated channels open B) Na+ flows inward C) K+ flows outward D) The inside of the membrane becomes momentarily positive E) The outside of the cell becomes momentarily positive _The observation that plasma membrane proteins mix after cell fusion provides evidence for: A) Rotational movement of plasma membrane proteins B) The bilayer structure of biomembranes C) The fluid mosaic model D) Interaction between the plasma membrane proteins from two different cell types (4 pts) Use the following information to calculate the resting membrane potential of a neuron (Condition 1). Assume R = 1.987 cal/mol-K, F= 23,062 cal/mol-volt, and T= 20°C Ion Na" KT cr [out], mM 440 20 560 [in], mM 50 400 50 Relative Permeability 0.04 1.00 0.45 (4 pts) What would the resting membrane potential be if the external concentration of Na+ were reduced to 220 mM (Condition 2)? (6 pts) How would the peak of the action potential differ between condition 1 and condition 2 above? (4 pts) You are an enzymologist (a scientist specializing in the study of enzyme structure and function) studying the enzyme that catalyzes the following reaction: E + S <-> ES o E + P where k\ and £3 are the rate constants for the forward reactions and where ki and £4 are the rate constants for the back reactions. If there is a gene mutation that results in an amino acid substitution that decreases k3 , then what effect, if any, will this have on Km and Fmax ? Answer increase, decrease, or no effect (4 pts) Explain the following observation as succinctly as possible. Protein A and protein B are membrane proteins with a molecular weight of 33,000. They each consist of a single polypeptide chain with 240 hydrophilic amino acid residues; and 60 hydrophobic amino acid residues. Protein A is an integral membrane protein and protein B is a peripheral membrane protein. Consider the following enzyme-catalyzed reaction: Galactose + ATP » Galactose-1-phosphate + ADP Assume that you have isolated the enzyme (galactokinase) for this reaction and have determined all the relevant kinetic parameters by varying the concentration of galactose in the presence of a constant saturating concentration of ATP. Following is a Lineweaver-Burk plot of the data. O.Z. <io — -2.0 -»0 10 30 i (3 pts) What is the value of Km of galactokinase for galactose under these assay conditions? (3 pts) What is the value of Vmax for galactokinase under these assay conditions? (4 pts) Assume that you now repeat the experiment, but this time vary the concentration of ATP while holding the concentration of galactose at high saturating levels. Assume that all other conditions are unchanged. What effect, if any, will this have on Vmax (Higher, Lower, Unchanged)? Explain your answer. An enzyme has a single active site at which it can bind and hydrolyze either X or Y. The enzyme cannot bind X and Y at the same time. A) (2 pts) Will Km for X be affected if Y is present in the reaction mixture? (Answer Yes or No) B) (2 pts) Will ^m for Y be affected if X is present in the reaction mixture? (Answer Yes or No) C) (4 pts) Will Fmax for X be affected if Y is present in the reaction mixture? (Answer Yes or No) Explain.