The Cell Cycle And Its Regulations

Question 1

Define cytokinesis

Answer 1

Cytoplasmic division following nuclear division resulting in two new daughter cells.

Question 2

Define interphase

Answer 2

Phase of a cell cycle where the cell is not dividing it is subdividing into growth and synthesis phases

Question 3

Define mitosis

Answer 3

Type of nuclear division that produces daughter cells genetically identical to each other and to the parent cell

Question 4

What are the two main checkpoints?

Answer 4

G1/S checkpoint (restriction point)
G2/M checkpoint

Question 5

What are the purposes of checkpoints?

Answer 5

Prevent uncontrolled division that would lead to cancer.

To detect and repair damage to DNA (damage caused by UV light)

Cycles cannot be reversed

DNA is only duplicated once during each cell cycle

Question 6

What is apoptosis?

Answer 6

Programmed cell death

Question 7

What is senescence?

Answer 7

Where they can no longer divide

Question 8

Role of M phase

Answer 8

A checkpoint chemical triggers condensation of chromatin.

Halfway through the cycle, the metaphase checkpoint ensures that the cell is ready to complete mitosis.

Question 9

Events within M phase

Answer 9

Cell growth stops

Nuclear division (mitosis)

Cytokinesis (cytoplasmic division)

Question 10

Role of G0 phase

Answer 10

A resting phase triggered during early G1 at the restriction point by a checkpoint chemical.

Some cells e.g. epithelial cells lining the gut, do not have this phase.

Question 11

Events within G0 phase

Answer 11

Cells may undergo apoptosis, differentiation, or senescence.

Some types of cells (e.g.neurones) remain in this phase for a long time/forever.

Question 12

Role of G1 (growth) phase

Answer 12

A G1 checkpoint control mechanism ensures that the cell is ready to enter the S phase and begin DNA synthesis.

Question 13

Events within G1 phase

Answer 13

Cells grow and increase in size

Transcription of genes to make RNA occurs.

Organelles duplicate .

Biosynthesis e.g. protein synthesis

The p53 (Tumour suppressor) gene helps control this phase.

Question 14

Role of S (synthesis) phase

Answer 14

Because the chromosomes are unwound and the DNA is diffuse, every molecule of DNA is replicated.

Question 15

What is the specific sequence of the replication of genes in S phase?

Answer 15

Housekeeping genes - those which are active in all types of cells are duplicated first.

Genes that are normally inactive in specific types of cells are replicated last.

Question 16

Events within the cell

Answer 16

Once the cell has entered this phase, it is committed to completing the cell cycle.

DNA replicates.

When all chromosomes have been duplicated each one consists of a pair of identical sister chromatids.

Phase is rapid and because the exposed DNA base pairs are more susceptible to mutagenic agents, reduced chances of spontaneous mutations happening.

Question 17

Role of G2 phase

Answer 17

Special chemicals ensure that the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and in formation of the spindle.

Question 18

Events in G2 phase

Answer 18

Cells grow