exam_2_key_demo

Exam_2_key_demo - Key for MCDB 100 Final Part 2 1(d 2(a(b and(d The rough ER consists of ER membranes and polyribosomes that are in the process of

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Key for MCDB 100 Final – Part 2 1) (d) 2) (a), (b), and (d) The rough ER consists of ER membranes and polyribosomes that are in the process of translating and translocating proteins into the ER membrane and lumen. Thus all proteins that end up in the lysosome, Golgi apparatus, or plasma membrane, or are secreted, will be encoded by the RNAs associated with the rough ER. Mitochondrial and ribosomal proteins are translated on free cytosolic ribosomes. 3) Choice (e) is the correct answer. Ions can pass either way through a channel; the direction in which flow takes place depends on the concentration gradient and the membrane potential. Some ion channels require a specific stimulus to open them; others, such as K + leak channels, do not (choice (a)). Ion channels are passive transporters and therefore require no energy source in order to function (choice (b)). Ion channels are very fast relative to carrier proteins but are limited by the rate at which ions can move through the channel (choice (c)). An ion channel allows specific positive or negative ions to pass, but not both (choice (d)). 4) (c) One function of actin filaments, but not microtubules, is to provide a meshwork beneath the plasma membrane that helps to form and strengthen this membrane. Microtubules have all of the other functions that are described. 5) (c) 6) (c) Sarcomeres contain actin filaments and myosin filaments that slide past each other during muscle contraction, leading to shortening of the sarcomere; the actin filaments and myosin filaments do not change in length. Flagella are microtubule-based structures that are not present on muscle cells. 7) (a), (e) At 37°C, the cells all have one genome worth of DNA, meaning that they have not replicated their DNA and therefore have not entered S phase. Hence they could either have a defect in initiation of DNA replication (a) or a defect that causes inappropriate delay in G 1 (e). 8) Choices (c) and (e) are correct. The concentration of mitotic cyclin, which contributes to the timing of mitosis (choice (e)), rises gradually during G 2 phase (thus (choice (a)) is incorrect) and is independent of the relatively constant level of Cdk (choice (b) is incorrect). In late M phase, mitotic cyclin is ubiquitinated and destroyed (choice (c)), thus falling to very low levels in G 1 phase (choice (d) is incorrect). 9) (c) The APC is active only in mid- to late-M phase. All the other statements are true. 10) (d) Cell size increases throughout interphase and not during M phase. All of the other phenomena are observed in M phase. 11) A—16; B—16; C—16; D—2; E—4 < sorry, I meant to modify this to a MC and forgot 12) Choice (c) is the correct answer. When the attachment to one kinetochore is severed, the whole chromosome moves to the opposite pole, showing that the kinetochore microtubules are pulling on their attached chromatid, not pushing it. The jiggling
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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_2_key_demo - Key for MCDB 100 Final Part 2 1(d 2(a(b and(d The rough ER consists of ER membranes and polyribosomes that are in the process of

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