18) Unit 1 - Control of the Cell Cycle

Question 1

why must the cell cycle be controlled

Answer 1

to ensure the cell cycle proceed in the CORRECT ORDER and everything happens in the CORRECT NUMBERS

Question 2

what regulates the cell cycle

Answer 2

checkpoints at various stage within the cell cycle.

Question 3

how do checkpoints regulate the cell cycle/ what happens at them?

Answer 3

stop and start signals at the checkpoints regulate the cell cycle

Question 4

name the 3 checkpoints

Answer 4

G1, G2, M (metaphase)

Question 5

what happens at the G1 checkpoint

Answer 5

• ensures that sufficient cell growth has occurred
• ensures there are enough proteins going into S for the duplication of the DNA complement
• ensures there are enough organelles

Question 6

What happens if the cell does not receive the ‘continue’ signal to go to the S phase from G1

Answer 6

It will go to the G0 phase

Question 7

Describe the G0 phase

Answer 7

•this is a non dividing state where the cell is stagnent

Question 8

what happens at the G2 checkpoint

Answer 8

•ensures the DNA replication is completed and there is enough duplicated DNA complement to be split in 2

Question 9

when does the M checkpoint occur and what happens at the M checkpoint

Answer 9

•occures during metaphase, controlling entry into anaphase

• ensures all the chcormosomes are alligned correctly at the metaphase plate
• ensures all chromosones are attached to spindle fibres
• therefore ensuring each daughter cell receieved the correct number of chromosomes

Question 10

whether a cell passes a checkpoint is dependant on?

Answer 10

regulatory proteins

Question 11

As the cell increases in size during G1 what happens to form active regulatory proteins

Answer 11

cyclin proteins accumulate and combine with regulatory proteins called cyclin-dependent kinases (Cdks) and activate them.

Question 12

what do CDK cause

Answer 12

cause the phosphorylation of proteins which stimulate the cell cycle (activate them)

If a sufficient threshold of phosphorylation of proteins is reached the cell cycle moves on to the next stage.

If an insufficient threshold is reached, the cell is held at a checkpoint

Question 13

CDK’s are used at all checkpoints so need to be regulated (activated and deactivated at the right checkpoints)

so how does a cell know which checkpoint should be active?

Answer 13

specific cyclins activate CDK’s for specific checkpoints.

e.g. G1 cyclin
G2 cyclin
M cyclin

Question 14

what is retinoblastoma

Answer 14

Rb is a regulatory protein in the cell cycle

Question 15

how does retinoblastoma work

Answer 15

• The non-phosphorylated form of Rb restricts progression from G1 to S phase, as it is a transcription factor inhibitor
• When the cell is ready to enter S phase from G1, the G1 CDK phosphorylates the Rb, making it inactive, (therefore it cannot inhibit transcription factors by binding to them.)
• This allows the essential genes to be transcribed that are needed for DNA replication - Therefore the cell enters S phase

Question 16

The cell cycle has ________ that can assess _________ _____and prevent it from continuing in the cell cycle

Answer 16

The cell cycle has proteins that can assess damaged DNA and prevent it from continuing in the cell cyle

Question 17

What happens when DNA is damanged in the cell cycle

Answer 17

Triggers the activation of p53, a protein which stimulates DNA repair, arrest of the cell cycle or cell death