Exam_1_practice_answer_key - Exam 1 practice answer key:...

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Exam 1 practice answer key: Multiple choice 1. (c) 2. (e) 3. (b) 4. Choice (e) is the answer. Hydrogen bonds are critical for maintaining the conformation, or 3-D structure, of biological macromolecules like proteins and nucleic acids. Choice (a) is false because hydrogen bonds are not covalent. Choice (b) is false because the nonpolar-CH groups on hydrocarbons cannot form good hydrogen bonds, in water or out of it. Choice (c) is essentially another way of stating choice (b) and thus is false. Choice (d) is false because many molecules besides water can form hydrogen bonds and do so regardless of whether or not water is present. 5. (c) An excess of ATP will initially restore the reactions, but as ATP is hydrolyzed, ADP will build up and inhibit the enzymes again. Pyrophosphate does not look like ATP and is therefore unlikely to be used by the enzymes as an alternative energy source. Pyrophosphate + enzyme D will just heat things up. What you need is a high-energy source of phosphate that can convert ADP back to ATP. Since the G ° of the reaction, ATP + creatine ADP + creatine phosphate, catalyzed by enzyme A is greater than zero, the addition of creatine phosphate and enzyme A can be used to form ATP from ADP, regenerating the ATP while also forming creatine as a waste product. 6. Choice (b) is the correct answer. At colder temperatures, the membrane will be less fluid. Hence, in order to maintain the status quo, the bacterium will have to take measures to increase membrane fluidity. Increasing the length of the hydrocarbon tails (choice (a)) would decrease membrane fluidity, while decreasing the number of glycolipids (choice (e)) would have little or no effect. Decreasing the proportion of fatty acid tails with no double bonds (fully saturated) (choice (c)) would decrease membrane fluidity. Bacteria do not have cholesterol (choice (d)). 7. (b) 8. Choice (e) is the correct answer. In transmembrane proteins that form an aqueous pore through the membrane, the pore is lined with hydrophilic amino acid side chains. The other statements are all true. Integral membrane proteins often precipitate in aqueous solutions because of their stretches of hydrophobic amino acids (choice (a)). Proteins also contain hydrophobic amino acids in parts of the protein other than the membrane-spanning region, for example, in the cores of their extracellular or cytoplasmic domains (choice (b)). Peripheral membrane proteins are attached to the membrane by noncovalent interactions with other membrane proteins, making their membrane association relatively weak and thus disruptable by gentle detergents (choice (c)).
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9. Choice (d) is the correct answer. Because the lipid bilayer is permeable to carbon dioxide and ethanol, destroying membrane proteins is unlikely to affect their exit (choices (a) and (b)). The lipid bilayer is also permeable to water (choice (e)). On the other hand glucose requires a membrane transport protein to be imported into the cell. ATP, which is a highly charged molecule, also requires a transport
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This note was uploaded on 08/04/2008 for the course CHEM 153A taught by Professor Staff during the Fall '05 term at UCLA.

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Exam_1_practice_answer_key - Exam 1 practice answer key:...

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