CHAPTER 18 THE CELL DIVISION CYCLE 2009 Garland Science Publishing Overview of the Cell Cycle 18 1 For each of the following sentences fill in the blanks with the best word or phrase selected from the list below Not all words or phrases will be used use each word or phrase only once The four phases of the cell cycle in order are G1 and A cell contains the most DNA after phase of the cell cycle A cell is smallest in size after phase of the cell cycle Growth occurs in and phases of the cell cycle A cell does not enter mitosis until it has completed synthesis DNA G1 G2 M nucleotide organelle protein S 18 2 What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only a Cells would not be able to replicate their DNA b The mitotic spindle could not assemble c Cells would get larger and larger d The cells produced would get smaller and smaller 18 3 A mutant yeast strain stops proliferating when shifted from 25 C to 37 C When these cells are analyzed at the two different temperatures using a machine that sorts cells according to the amount of DNA they contain the graphs in Figure Q18 3 are obtained Figure Q18 3 Which of the following would not explain the results with the mutant a inability to initiate DNA replication b inability to begin M phase c inability to activate proteins needed to enter S phase d inappropriate production of a signal that causes the cells to remain in G1 18 4 Which of the following events does not usually occur during interphase a Cells grow in size b The nuclear envelope breaks down c DNA is replicated d The centrosomes are duplicated 18 5 What would happen to the progeny of a cell that proceeded to mitosis and cell division after entering S phase but had not completed S phase Keep in mind that highly condensed chromatin including the centromere region is replicated late in S phase Explain your answer 18 6 Are the statements below true or false Explain your answer A Statement 1 Generally in a given organism the S G2 and M phases of the cell cycle take a defined and stereotyped amount of time in most cells B Statement 2 Therefore the cell cycle control system operates primarily by a timing mechanism in which the entry into one phase starts a timer set for sufficient time to complete the required tasks After a given amount of time has elapsed a molecular alarm triggers movement to the next phase 18 7 Which of the following statements about the cell cycle is false a Once a cell decides to enter the cell cycle the time from start to finish is the same in all eucaryotic cells b An unfavorable environment can cause cells to arrest in G1 c A cell has more DNA during G2 than it did in G1 d The cleavage divisions that occur in an early embryo have short G1 and G2 phases 18 8 Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2 a The cell would be unable to enter M phase b The cell would be unable to enter G2 c The cell would enter M phase under conditions when normal cells would not d The cell would pass through M phase more slowly than normal cells How We Know Discovery of Cyclins and Cdks 18 9 For each of the following sentences fill in the blanks with the best word or phrase selected from the list below Not all words or phrases will be used each word or phrase should be used only once Many features of cells make them suitable for biochemical studies of the cell cycle control system For example the cells are unusually large and are arrested in a like phase When the cells are triggered to resume cycling the cell divisions have especially G1 and G2 phases and occur Studies with Xenopus eggs identified a partly purified activity called that drives a resting Xenopus oocyte into M phase MPF activity was found to during the cell cycle although the amount of its kinase component called remained constant The regulatory component of MPF called has a effect on MPF activity and plays a part in regulating interactions with its s The components of MPF are evolutionarily from yeast to humans so that the corresponding human genes are to function in yeast able asynchronously Cdk conserved cyclin divergent egg fibroblast G1 G2 hexokinase inhibitory long M maturation promoting factor oscillate PI 3 kinase regulin S short sperm steady stimulatory substrate synchronously ubiquitin unable uniform 18 10 MPF activity was discovered when cytoplasm from a Xenopus M phase cell was injected into Xenopus oocytes inducing the oocytes to form a mitotic spindle In a control experiment Xenopus interphase cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle Which of the following statements is not a legitimate conclusion from the control experiment a The piercing of the oocyte membrane by a needle is insufficient to cause mitotic spindle formation b An increased volume of cytoplasm is insufficient to cause mitotic spindle formation c Injection of extra RNA molecules is insufficient to cause mitotic spindle formation d Components of an interphase nucleus are insufficient to cause mitotic spindle formation 18 11 Which of the following is not good direct evidence that the cell cycle control system is conserved through billions of years of divergent evolution a A yeast cell lacking Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle b The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cylins in humans c The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast d Yeast cells have only one Cdk whereas humans have many Cdks The Cell Cycle Control System 18 12 Levels of Cdk activity change during the cell cycle in part because a the Cdks phosphorylate each other b the Cdks activate the cyclins c Cdk degradation precedes entry into the next phase of the cell cycle d cyclin levels change during the cycle 18 13 The concentration of mitotic cyclin M cyclin a rises markedly during M phase b is activated by phosphorylation c falls toward the end of M phase as a result of ubiquitylation and degradation d is highest in G1 phase 18 14 You have isolated a strain of mutant yeast cells that divides normally at 30 C but cannot enter M phase at 37 C You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M Cdk complex at both temperatures Which of the following