MCB 252 Exam 3 Question Examples Rivier KEY

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University of Illinois, Urbana Champaign *

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Biology

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Feb 20, 2024

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1 NAME:_____________________________ _________NETWORK ID:__________________ SECTION:__________________________ TA:_____________________________ MCB 252 Old Exam 3 Key This exam consists of 60 questions for a total of 175 points. Choose the BEST answer from the available choices. Questions 1-10 are worth 2 points each. 1. In lecture we discussed the fact that actin plays a role in phagocytosis. Based on that discussion, do you expect that addition of latrunculin to cells would stop phagocytosis? A. Yes, latrunculin would stop phagocytosis. B. No, latrunculin would not stop phagocytosis. 2. As discussed in lecture, the contractile bundles (sarcomeres) found in muscle cells most likely appeared in evolution before the contractile bundles found in stress fibers. A. TRUE B. FALSE 3. Intermediate filaments are considered equilibrium polymers, as opposed to actin filaments which are best described as steady state filaments. A. TRUE B. FALSE 4. As described in lecture, because actin filaments are helical, any motor protein that moves along those filaments must follow a helical path. A. TRUE B. FALSE 5. As described in lecture, a polyclonal antibody contains many different antibodies, each of which recognizes a distinct epitope on the surface of an antigen. A. TRUE

2 B. FALSE 6. Profilin binds to which end of an actin monomer? A. The plus end B. The minus end 7. Exon shuffling occurs at the level of DNA in the genome; whereas, splicing occurs at the level of RNA. A. TRUE B. FALSE 8. As described in lecture, Homo sapiens migrated out of Africa before Neanderthals migrated out of Africa. A. TRUE B. FALSE 9. In lecture, we discussed the modular construction of some genes and the evolution of genes (and proteins) by the addition of domains. As described in lecture, this process occurs in prokaryotes and eukaryotes. A. TRUE B. FALSE 10. As described in lecture, all cytoskeletal polymers are multi-stranded. A. TRUE B. FALSE Questions 11-55 are worth 3 points each. 11. Which property of eukaryotic gene regulatory regions, as discussed in lecture, allowed for the evolution complex regulatory regions?

3 A. That core promoters act over precise distances B. That there are different types of core promoters C. That eukaryotic genes have a regulatory promoter D. That enhancers can act over long distances E. Both A and B are correct. 12. Which of the following statements is/are TRUE, and which is/are FALSE? i = The majority of different colors of fluorescent proteins used by cell biologist are all naturally occurring proteins that were isolated from different types of aquatic organisms. ii = As described in lecture, when purifying a protein of interest one needs an assay that is specific for that particular protein. A. Both i and ii are TRUE. B. i is TRUE, and ii is FALSE. C. i is FALSE, and ii is TRUE. D. Both i and ii are FALSE. The next two questions are linked. 13. Congratulations! You finally managed to build a ray gun that allows you to shrink yourself down to the size of a molecule. Like any normal person, your first idea is to stand on top of a

4 formin protein. That formin protein that you are standing on is immobilized on a solid surface. Actin monomers then start to arrive at the formin upon which you are standing. Looking down the filament, what do you see? A. A steady stream of actin subunits moving towards you. B. The minus end of the actin filament is moving away from you. C. The plus end of the actin filament moving away from you. D. Nothing is moving because formins cap the (+) ends of filaments such that they do not grow. E. Nothing is moving because formins cap the (– ) ends of filaments such that they do not grow. 14. You have now elected to stand on an Arp2/3 complex. The Arp2/3 complex just nucleated a new actin filament, and that daughter filament has polymerized to add several thousand actin subunits. Now you see that a myosin II molecule (similar to the myosin that drives muscle contraction) has landed on the middle of the daughter filament produced by the Arp2/3 molecule upon which you are standing. What do you see? A. Yikes! Better jump off the Arp2/3 because the myosin is moving towards you very rapidly! B. No worries. The myosin is moving away from you. C. Hard to tell as there is an equal probability that the myosin will move away from the Arp2/3 or towards the Arp2/3. D. Hard to tell as the Arp2/3 complex binds to either end of the actin filament. E. Myosin motors do not move on actin filaments. 15. Which of the following does not require one or more motor proteins for movement? A. Muscle contraction B. Contraction of a contractile bundle that is part of a stress fiber C. Cytoplasmic streaming D. Movement of Listeria in the cytoplasm of eukaryotic cells E. All of the above require one or more motor proteins. 16. As discussed in lecture, there are approximately how many different types of cells in humans? A. 51 B. 210 C. 710 D. 1,710 E. 7,100 17. In order to determine the structure of a protein by X-ray crystallography you need which of the following?

5 A. The protein of interest needs to be purified. B. You need to know the amino acid sequence of the protein of interest. C. You need to know the approximate shape of the protein from electron microscopy. D. Both A and B E. All of the above (A, B, and C) 18. Which of the following is correct with regard to the two statements below? i = As described in lecture, the concentration of actin monomers in cells is approximately 100x the critical concentration. ii = As described in lecture, the plus end of a typical actin filament has a higher critical concentration than the minus end. A. Both i and ii are TRUE. B. i is TRUE, and ii is FALSE. C. i is FALSE, and ii is TRUE. D. Both i and ii are FALSE. 19. Which step in the ATPase cycle of myosin II results in rotation of the head into the “cocked” position? A. Binding of ATP to the myosin head B. Hydrolysis of ATP to ADP + P i C. Release of P i from the myosin head D. Release of ADP from the myosin head E. None of the above are correct. 20. The figure below was discussed in lecture. This figure refers to myosin family members.

6 Which of the two statements below is/are TRUE, and which is/are FALSE? i = Dictyostelium MIA myosin is more closely related to Acanthamoeba HMW myosin than it is to Human brush border MI myosin. ii = Chicken MV myosin is more closely related to Budding yeast Myo4 than it is to Acanthamoeba MII. A. i and ii are both TRUE. B. i is TRUE, and ii is FALSE. C. i is FALSE, and ii is TRUE. D. i and ii are both FALSE. 21. UIUC alumnus James Spudich studies hypertrophic cardiomyopathy (HCM). The hearts of people suffering from HCM contract with more average force than the hearts of people who do not have this disease. As a result of the increase force of contraction, the heart wall thickens in patients with HCM which eventually leads to a sudden heart attack and premature

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