Chapter 18 & 19 Answers

Chapter 18 & 19 Answers - Study Guide Chapter 18...

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Study Guide Chapter 18 Answers 1. The four phases of the cell cycle, in order, are G 1 , S , G 2 , and M . A cell contains the most DNA after S phase of the cell cycle. A cell is smallest in size after M phase of the cell cycle. Growth occurs in G 1 , S , and G 2 phases of the cell cycle. A cell does not enter mitosis until it has completed DNA synthesis. 2 The cells produced would get smaller and smaller, as they would not have sufficient time to double their mass before dividing. 3. The daughter cells would probably die. Those chromosomes that had not completed replication in S phase would have only one centromere, as the centromere is the last part of the chromosome to be replicated, and would therefore be segregated to only one of the two daughter cells at random. At least one, and probably both, of the daughter cells would thus receive an incomplete set of chromosomes and would be unlikely to be viable. Even if one daughter cell, by chance, received a full set of chromosomes, some of these chromosomes would be incompletely replicated and the cell would probably still not be viable. 4 A. True. In nearly all cells in an organism, the S, G 2 , and M phases of the cell cycle take the same amount of time. The different timing of cell division in different cell types is due to variable lengths of the G 1 phase or to withdrawal into the G 0 state. B. False. The cell-cycle control system does use a timing mechanism of sorts, but it also employs various surveillance and feedback mechanisms. Cells will not embark on later events or phases until the earlier events or phases are completed successfully. In response to a defect or a delay in cell-cycle events, cells engage molecular brakes to arrest the progression of the cell cycle at various checkpoints in order to allow time for completion or repair. 5. 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
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Chapter 18 & 19 Answers - Study Guide Chapter 18...

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