Question

Cell biology

1. Briefly describe what occurs in the four phases of the cell cycle (G₁, S, G₂, M).

2. How does cyclin regulate cyclin-dependent kinases (Cdks)? Why do Cdks require cyclin?

3. Mitogens are involved in cell signaling pathways which promote cell division by the production of cyclin. Using the figure 18-14 from your book (which is on the right), answer whether the expression of genes required for cell proliferation will be increased or decreased under the following scenarios.

a. Mutation in the Rb protein which prevents it from being phosphorylated by G₁-Cdk complex.

b. Alterations in the signal transduction from the activated mitogen receptor so that G₁-Cdk complex is not activated.

c. Increased activation of the G1-Cdk complex.

4. In which phase of the cell cycle does the average cell spend its most time? _______________________________

5. Before a cell undergoes mitotic cell division:

a. what has to happen first, regarding its DNA?

b. If (what you wrote in 2a) didn’t happen, what problem would arise?

6. There are some cells which after they mature (fully differentiate into their specific cell type) never undergo division (such as heart muscle cells) again. These cells are in what phase? _________

7. How are phosphates involved in regulating the activity of a cyclin-dependent kinase (Cdks)?

7. How does cytochrome c initiate apoptosis? What are the roles of Bax and Bak in this initiation? How does Bcl affect apoptosis?

8. For the list below, indicate which statements are true of the G1, G2, S, or M phase of the cell cycle. A statement may be true of any or all of the phases.

a. _______ the amount of nuclear DNA doubles

b. _______ the nuclear envelope breaks into fragments

c. _______ sister chromatids separate from one another

d. _______ cell that never divide again will be in this stage

e. _______ chromosomes are present in a condensed state

f. _______ mitotic cyclin is at its highest level

g. _______ a Cdk protein is present in the cell

h. _______ a cell cycle checkpoint has been identified in this phase

i. ________ nuclear envelope reforms

j. ________ cohesion proteins break down

k. ________ cell is active in doing its “job”

l. _________ cell is getting ready to make proteins needed for cell division

m. __________ S cyclin is at its lowest concentration

Answer 1

1. G1 PHASE is Gap 1 and protein for DNA replication are synthesized in it.

S phase include DNA replication

G2 phase synthesize protein for cell division.

M phase is phase in which cell divide.

2. Cyclin activates Cyclin dependent kinases are enzyme which induce replication and production of protein required in cell cycle.

3a. Mutation in Rb inhibiting the G1 Cdk stops the cell cycle in G1 phase.

b. Also cell divison stops due to non signa transduction.

c. It will cause continous divison.

4. S phase takes largest duration and replicate the DNA.