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Essential cell biology CH final exam 2023 question
and correct graded A+ Answers
What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only? Cells would not be able to replicate their DNA. The mitotic spindle could not assemble. Cells would get larger and larger. The cells produced would get smaller and smaller. Which of the following events does not usually occur during interphase? Cells grow in size. The nuclear envelope breaks down. DNA is replicated. The centrosomes are duplicated In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated? at the transition between G1 and S when cells enter G during M at the end of G2 - Which of the following statements about the cell cycle is false? Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells. An unfavorable environment can cause cells to arrest in G1. A cell has more DNA during G2 than it did in G1. The cleavage divisions that occur in an early embryo have short G1 and G2 phases. - answer-a
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? The cell would be unable to enter M phase. The cell would be unable to enter G2. The cell would enter M phase under conditions when normal cells would not. The cell would pass through M phase more slowly than normal cells Progression through the cell cycle requires a cyclin to bind to a Cdk because _________. the cyclins are the molecules with the enzymatic activity in the complex. the binding of a cyclin to Cdk is required for Cdk enzymatic activity. cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle. without cyclin binding, a cell-cycle checkpoint will be activated. Levels of Cdk activity change during the cell cycle, in part because ________________. the Cdks phosphorylate each other. the Cdks activate the cyclins. Cdk degradation precedes entry into the next phase of the cell cycle. cyclin levels change during the cycle. The concentration of mitotic cyclin (M cyclin) ________________. rises markedly during M phase. is activated by phosphorylation. falls toward the end of M phase as a result of ubiquitylation and degradation. (d) is highest in G1 phase. - 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 temperaturesensitive mutations could not be responsible for the behavior of this strain of yeast?
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 yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle. The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in humans. The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast. Yeast cells have only one Cdk, whereas humans have many Cdks. Mitogens are _____. extracellular signals that stimulate cell division. transcription factors important for cyclin production. kinases that cause cells to grow in size. produced by mitotic cells to keep nearby neighboring cells from dividing. The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______. phosphorylating Cdk. marking cyclins for destruction by proteolysis. inhibiting cyclin transcription. activating apoptosis. The G1 DNA damage checkpoint ________________. causes cells to proceed through S phase more quickly. involves the degradation of p53. is activated by errors caused during DNA replication. involves the inhibition of cyclin-Cdk complexes by p21. - answer-d Cells in the G0 state ________________. do not divide. cannot re-enter the cell cycle.
have entered this arrest state from either G1 or G2. have duplicated their DNA. Which of the following statements is false? DNA synthesis begins at origins of replication. The loading of the origin recognition complexes (ORCs) is triggered by S-Cdk. The phosphorylation and degradation of Cdc6 help to ensure that DNA is replicated only once in each cell cycle. DNA synthesis can only begin after prereplicative complexes assemble on the ORCs. How does S-Cdk help guarantee that replication occurs only once during each cell cycle? It blocks the rise of Cdc6 concentrations early in G1. It phosphorylates and inactivates DNA helicase. It phosphorylates the Cdc6 protein, marking it for destruction. It promotes the assembly of a prereplicative complex. You create cells with a version of Cdc6 that cannot be phosphorylated and thus cannot be degraded. Which of the following statements describes the likely consequence of this change in Cdc6? Cells will enter S phase prematurely. Cells will be unable to complete DNA synthesis. The origin recognition complex (ORC) will be unable to bind to DNA. (d) Cdc6 will be produced inappropriately during M phase - Which of the following does not occur during M phase in animal cells? growth of the cell condensation of chromosomes breakdown of nuclear envelope attachment of chromosomes to microtubules -
Which of the following statements about kinetochores is true? Kinetochores assemble onto chromosomes during late prophase. Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome. Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules. Kinetochores assemble on chromosomes that lack centromeres. - answer-a A friend declares that chromosomes are held at the metaphase plate by microtubules that push on each chromosome from opposite sides. Which of the following observations does not support your belief that the microtubules are pulling on the chromosomes? the jiggling movement of chromosomes at the metaphase plate the way in which chromosomes behave when the attachment between sister chromatids is severed the way in which chromosomes behave when the attachment to one kinetochore is severed the shape of chromosomes as they move toward the spindle poles at anaphase - answer-a Which of the following statements about the anaphase-promoting complex (APC) is false? It promotes the degradation of proteins that regulate M phase. It inhibits M-Cdk activity. It is continuously active throughout the cell cycle. M-Cdk stimulates its activity. - answer-c Which of the following statements is true? Anaphase A must be completed before anaphase B can take place. In cells in which anaphase B predominates, the spindle will elongate much less than in cells in which anaphase A dominates. In anaphase A, both kinetochore and interpolar microtubules shorten. In anaphase B, microtubules associated with the cell cortex shorten. - answer-d
When introduced into mitotic cells, which of the following is expected to impair anaphase B but not anaphase A? an antibody against myosin ATPγS, a nonhydrolyzable ATP analog that binds to and inhibits ATPases an antibody against the motor proteins that move from the plus end of microtubules to the minus end an antibody against the motor proteins that move from the minus end of microtubules toward the plus end - answer-d Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells? assembly of the contractile ring decondensation of chromosomes reassembly of the nuclear lamina transcription of nuclear genes - answer-a A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to ________________. reassemble its nuclear envelope at telophase. disassemble its nuclear lamina at prometaphase. begin to assemble a mitotic spindle. condense its chromosomes at prophase. - answer-b Cytokinesis in animal cells ________________. requires ATP. leaves a small circular "scar" of actin filaments on the inner surface of the plasma membrane. (c) is often followed by phosphorylation of integrins in the plasma membrane. (d) is assisted by motor proteins that pull on microtubules attached to the cell cortex. - answer-a Which of the following statements is false? The cleavage furrow is a puckering of the plasma membrane caused by the constriction of a ring of filaments attached to the plasma membrane. The cleavage furrow will not begin to form in the absence of a mitotic spindle.
Which of the following statements about apoptosis is true? Cells that constitutively express Bcl2 will be more prone to undergo apoptosis. The prodomain of procaspases contains the catalytic activity necessary for procaspase activation. Bax and Bak promote apoptosis by binding to procaspases in the apoptosome. Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria. - answer-d
