Cell proliferation

Question 1

What are the phases in Cell cycle

Answer 1

G1–>S–>G2–>M–>G0 (optional)

Question 2

What is the G1 phase doing

Answer 2

Growing in cell size and preparation for DNA replication

Question 3

What is S phase doing

Answer 3

DNA replication

Question 4

What is G2 phase doing

Answer 4

Checking for error in DNA replication and prep for cell division

Question 5

Name the 2 parts of M phase

Answer 5

Mitosis and Cytokinesis

Question 6

What is G0

Answer 6

Temporary or permanent stop dividing and enter a quiscence phase

Question 7

At what stage the chromosome becomesX shaped

Answer 7

S stage

Question 8

What is the fate of the 2 chromatids

Answer 8

Become daughter chromosomes

Question 9

What is homologous chromosomes

Answer 9

Pair of chromosomes that are similar in size, shape and carries gene that controls the same inherited characteristics

Question 10

At which stage is the cell a diploid

Answer 10

G1, after replication

Question 11

Other than diploid, name another state that the cell can be

Answer 11

Tetraploid

Question 12

What are the 3 checkpoints and what do they look for

Answer 12

G1–>S: Environment favourable? Large enough cell size? DNA damage?

G2–>M: Large enough cell size? All DNA replicated? All DNA damage repaired?

M:All chromosomes attached to spindle fibre?
–> Pull them apart

Question 13

What is the family of molecules that regulated cell cycle called

Answer 13

Cyclin-cyclin-dependent kinase complexes

Question 14

What is the G1 cyclin refers to. Under what circumstances is it activated and what’s it’s activity. What is the significance

Answer 14

It means Cyclin D Ckd 4/6. It is activated to release Cyclin D when Growth factor is sufficient. It reflects the Nutrient availabilty, stress factor and growth factor

Question 15

Name the tumour suppressor protein which acts on DNA. How does it work

Answer 15

Prb (Rb), can inhibit E2F, which is a transcription factor, hence no cyclin E can be formed to start S phase

Question 15

Name the Tumour suppressor that look for DNA damage. Suggest how it works

Answer 15

p53. ATR ATM binds to DNA and look for DNA damage. When one is detected, it activiate Chk2 which phosphorylates p53 and separate it from MdM2 which breaks it down by polyubiquitylation, making p53 activated instead of being degraded.

It can activate p21 gene to make p21 protein which inhibit Cyclin Cdk1, Cyclin Cdk2, Cyclin Cdk 4/6

Question 16

What are the signifance to pause cell cycle

Answer 16

To allow time for DNA repair or apoptosis

Question 17

What is the S phase Cyclin

Answer 17

Cycin E Cdk2

Question 18

How does Cyclin E Cdk2 prevent duplicating DNA twice

Answer 18

It phosphorylate the Cdt1 and Cdt6 on the replication bubble so that they are hyperphosphorylated and cannot function to replicate

Question 19

What is the Mphase Cyclin refering to

Answer 19

Cyclin B Cdk1

Question 20

What are the site of phosphorylation on M phase Cyclin for

Answer 20

Deactivating it

Question 21

Name the protein activating M phase Cyclin and why it is activated only after replication

Answer 21

The Cdc 25 protein .
It is inhibited by Chk1 in the replication state as long as the Chk1 is activated by the ATR protein in S/G2 phase

Question 22

What is the importance of Cyclin B/Cdk 1

Answer 22

It breaks down the intermediate filament, ie Lamin

As well as phosphorlyating the condensin to condense the chromosomes

Question 23

What is the fate of it after replication

Answer 23

It is degraded by polyubiquitinylion

Question 24

What is the proteins M phase checkpoint detecting

Answer 24

It detect the tension on the mitoic spindle and checks if they are equal

Question 25

What is the mechanism

Answer 25

Under inequal tension, it will be detected by the tension sensor to activate proteins like the Mad 1/2/3 proteins. The Mad proteins will inhibit APC (anaphase-promoting comoplex), hence APC cannot degrade the securin and the securin can hold the separas complex to make separase not able to separate the chromosomes