Cell Cycle

Question 1

Purpose of the cell cycle

Answer 1

To regulate the growth and replacement of genetically identical cells throughout the life of the organism

Question 2

Order of the cell cycle

Answer 2

G1 > S > G2 > M

Question 3

What is interphase?

Answer 3

G1, S and G2 phases. Very active period of growth

Question 4

G1 phase

Answer 4

1st growth stage. Cell makes new proteins and copies of organelles

Question 5

S phase

Answer 5

DNA replication occurs

Question 6

G2 phase

Answer 6

2nd period of cell growth. Cell makes more proteins and copies the organelles in preparation for mitosis

Question 7

What does the M phase consist of?

Answer 7

Mitosis and cytokinesis

Question 8

What are the stages of mitosis?

Answer 8

Prophase, metaphase, anaphase, telophase

Question 9

Prophase

Answer 9

Chromosomes coil up. Microtubules starts to form spindle fibres and attach to the kinetichores at the centromeres. Nuclear membrane disintegrates.

Question 10

Metaphase

Answer 10

Chromosomes line up on the metaphase plate at the equator

Question 11

Anaphase

Answer 11

Spindle fibres pull sister chromatids apart

Question 12

Telophase

Answer 12

Separated chromosomes pulled by spindle fibres to opposite poles to form daughter nuclei. Chromosomes start to uncoil and nuclear membrane is formed

Question 13

Cytokinesis

Answer 13

Division of the cytoplasm to form two daughter cells

Question 14

Importance of cell-cycle control

Answer 14

Uncontrolled reduction in the rate of the cell cycle can result in degenerative diseases such as Alzheimer’s
Uncontrolled increase in the rate can result in tumour formation

Question 15

G1 checkpoint

Answer 15

Near the end of G1. Cell size is monitored. Controls entry to S phase

Question 16

What happens if cells don’t pass G1 checkpoint?

Answer 16

Cells switch to a non-dividing state called G0 phase. Can return if conditions change

Question 17

G2 checkpoint

Answer 17

End of G2 phase. Assesses success of DNA replication. Controls entry to mitosis

Question 18

M checkpoint

Answer 18

During metaphase. Monitors chromosome alignment. Controls entry to anaphase, thus triggers exit from mitosis and the start of cytokinesis

Question 19

Cyclin-dependent kinase (CDKs)

Answer 19

Controls G1 checkpoint. Regulatory proteins that are activated by combining with cyclin proteins. They cause the phosphorylation of target proteins that stimulate the cell cycle. Without active CDKs the cell will enter G0 resting state.

Question 20

Retinoblastoma protein (Rb)

Answer 20

Transcription-factor inhibitor. Binds to transcription factor E2F which inhibits the transcription of the genes required to enter S phase.

Question 21

P53 protein

Answer 21

Can stimulate DNA repair, arrest the cell cycle or trigger cell death (apoptosis)