Molecular Cell Bio Chapter 18

Condensins

 

1. are degraded when cells enter M phase.

2. assemble into complexes on the DNA when phosphorylated by M-Cdk.

3. are involved in holding sister chromatids together.

4. bind to DNA before DNA replication begins.

2

Progression through the cell cycle requires a cyclin to bind to a Cdk because

 

1. the cyclins are the molecules with the enzymatic activity in the complex.

2. the binding of a cyclin to Cdk is required for Cdk enzymatic activity.

3. cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle.

4. without cyclin binding, a cell-cycle checkpoint will be activated.

2

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only?

 

1. The cells would not be able to replicate their DNA.

2. The mitotic spindle could not assemble.

3. The cells produced would be larger than if G1 were also present.

4. The cells produced would be smaller than if G1 were also present.

4

The G₁ DNA damage checkpoint

 

1. causes cells to proceed through S phase more quickly.

2. involves the degradation of p53.

3. is activated by errors caused during DNA replication.

4. involves the inhibition of cyclin–Cdk complexes by p21.

4

Which of the following statements is FALSE?

 

1. Cdc25 dephosphorylation of Wee1 activates the kinase, promoting the G2/M transition.

2. Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive.

3. Inhibiting the Cdc25 phosphatase will delay the G2/M transition.

4. The activating phosphatase (Cdc25) removes the phosphates from mitotic Cdk that were added by Wee1, so that M-Cdk will be active.

1

Which of the following statements is FALSE?

 

1. DNA synthesis begins at origins of replication.

2. The loading of the origin recognition complexes (ORCs) is triggered by S-Cdk.

3. The phosphorylation and degradation of Cdc6 help to ensure that DNA is replicated only once in each cell cycle.

4. DNA synthesis can only begin after prereplicative complexes assemble on the ORCs.

2

Which of the following statements about the cell cycle is FALSE?

 

1. Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.

2. An unfavorable environment can cause cells to arrest in G₁.

3. A cell has more DNA during G₂ than it did in G₁.

4. The cleavage divisions that occur in an early embryo have short G₁ and G₂ phases.

1

You create cells with a version of the origin recognition complex, ORC, that cannot be phosphorylated by S-Cdk and thus cannot be inactivated. Which of the following statements describes the likely consequence of this change in ORC?

 

1. Cells will enter S phase prematurely.

2. Cells will replicate some regions of the genome more than once in a cell cycle.

3. ORC will be unable to bind to DNA.

4. DNA helicases will not be able to open the double helix at the replication origin.

2

The retinoblastoma (Rb) protein blocks cells from entering the cell cycle by

 

1. phosphorylating Cdk.

2. marking cyclins for destruction by proteolysis.

3. inhibiting cyclin transcription.

4. activating apoptosis.

3

Which word or phrase below best describes the phase in mitosis depicted in Figure 18-2?

Figure 18-2

 

1. anaphase

2. prometaphase

3. S-phase checkpoint

4. metaphase

4

Which letter is associated with the line that is pointing to the kinetochore microtubules in Figure 18-2?

Figure 18-2

 

1. A

2. B

3. C

4. D

4

How does S-Cdk help guarantee that replication occurs only once during each cell cycle?

 

1. It blocks the rise of Cdc6 concentrations early in G₁.

2. It phosphorylates and inactivates DNA helicase.

3. It phosphorylates and inactivates Cdc6.

4. It promotes the assembly of a prereplicative complex.

3

You engineer yeast cells that express the M cyclin during S phase by replacing the gene regulatory sequences of the M cyclin gene with those of the S cyclin gene. Keeping in mind that yeast cells have one common Cdk that binds to all cyclins, which of the following outcomes is LEAST likely during this experiment?

 

1. There will be both M cyclin–Cdk and S cyclin–Cdk complexes in the cell during S phase.

2. Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S phase.

3. G₁ cyclin–Cdks will be activated earlier in G1.

4. S-Cdk targets will be phosphorylated during S phase.

3

In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated?

 

1. at the transition between G₁ and S

2. when cells enter G₀

3. during M

4. at the end of G₂

4

At the end of DNA replication, the sister chromatids are held together by the

 

1. kinetochores.

2. securins.

3. cohesins.

4. histones.

3

Sister chromatid separation occurs because __________ are destroyed by the APC/C.

 

1. securins

2. cohesins

3. kinetochores

4. condensins

1

Mitogens are

 

1. extracellular signals that stimulate cell division.

2. transcription factors important for cyclin production.

3. kinases that cause cells to grow.

4. produced by mitotic cells to keep nearby neighboring cells from dividing.

1

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 18-1 are obtained.

Figure 18-1

Which of the following would NOT explain the results with the mutant?

 

1. inability to initiate DNA replication

2. inability to begin M phase

3. inability to activate proteins needed to enter S phase

4. inappropriate signal that causes the cells to remain in G₁

2

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?

 

1. The cell would be unable to enter M phase.

2. The cell would be unable to enter G₂.

3. The cell would enter M phase under conditions when normal cells would not.

4. The cell would pass through M phase more slowly than normal cells.

3

The concentration of mitotic cyclin (M cyclin)

 

1. rises markedly during M phase.

2. is activated by phosphorylation.

3. falls toward the end of M phase because of ubiquitylation and degradation.

4. is highest in G₁ phase.

3