The Cell Cycle

Question 1

phases

Answer 1

(G0) -> G1 -> S -> G2 -> M

Question 2

what happens in G0

Answer 2

phase when cells are not actively dividing
- quiescence
- not always permanent
response to an external signal mitogenic factor

Question 3

what happens G1

Answer 3

growing in size (back to optimal)
monitoring environment (restriction point)
RNA + protein synthesis for S phase
growth factor dependant

Question 4

what happens in S phase

Answer 4

synthesis of DNA

Question 5

what happens in G2

Answer 5

further growth
cell organelle replication
prep for mitosis

Question 6

what happens in M phase

Answer 6

mitosis
cytokinesis

Question 7

Mitosis phases

Answer 7

prophase -> prometaphase -> metaphase/ equatorial phase -> anaphase -> telophase

Question 8

what happens in prophase

Answer 8

chromosomes shorten and become visible
outside the nucleus, the two centrioles separate and move to different poles
parallel tubules are assembled to create the mitotic spindle

Question 9

what happens in prometaphase

Answer 9

nuclear envelope disappears + spindle microtubules extend into central region of the cell, attaching to chromosomes

Question 10

what happens in metaphase

Answer 10

chromosomes align at the centre of the cell

Question 11

what happens in anaphase

Answer 11

cleavage of proteins that hold the chromatids together
- allows movement to opposite ends of the spindle via microtubule-generated pulling forces
sister chromatids grouped at opposite ends of the cell and both groups are diploid in number

Question 12

what happens in telophase

Answer 12

nuclear envelope reforms
chromosomes decondense
spindles disintegrate

Question 13

what are the checkpoints in the cell cycle

Answer 13

restriction point (G1)
DNA damage checkpoints (G1 + G2)
metaphase checkpoint (M phase)

Question 14

what happens at the restriction point

Answer 14

commitment step into the cell cycle
progression is determined by the presence of growth factors (progression/ arrest)
growth factors not required after this point
- dependant on the accumulation of cyclin D
- 2-3 hours prior to initiation
- Retinoblastoma (RB) protein

Question 15

restriction point pathway

Answer 15

growth factor -> Ras pathway -> CDK 4/6-cyclin D -> (ATP -> ADP) phosphorylates RB -> E2F exposed -> gene transcription -> mRNA translation -> enzymes and other proteins for S phase

Question 16

what is RB

Answer 16

a tumour suppressor gene

Question 17

what happens at the DNA damage checkpoints

Answer 17

damage is detected by p53
- leads to production of cyclin-dependant kinase inhibitor p21
p53 is a transcription factor
- low level damage = p21
- high level damage = express genes for apoptosis
- protects integrity of genome

Question 18

what happens at the metaphase checkpoint

Answer 18

makes sure that chromosomes are attached to the spindle tubules

Question 19

CDK 4/6

Answer 19

cyclin D
G1 -> S transition
allows cell to enter the cell cycle
substrate + RB protein

Question 20

CDK 1

Answer 20

cyclin B
- moves cell into M phase
- phosphorylates Lamins and condensins -> products for M phase

Question 21

what are cyclins

Answer 21

small short lived proteins that must by associate with CDKs in order for them to be active
increased synthesis of cyclin occurs until threshold is reached and begins to bind with CDK molecules
phosphorylation/ dephosphorylation

Question 22

what are CKIs

Answer 22

• block cyclin/ CDK activity
• either forms an inactive complex or acts as a competitive CDK ligands
• three families; p21 CIP; p27 KIP; p16 INK

Question 23

process of cyclins

Answer 23

net phosphorylated state (inactive form)
after binding with CDK, net loss of phosphorylation
becomes an active kinase -> phosphorylates things
breakdown of the nuclear membrane - active kinase phosphorylates lamins -> disassembly of intermediate filaments + destruction of nuclear laminar
chromosome condensation - phosphorylate condensins and histones
spindle formation -> phosphorylate microtubule-associated proteins MAPs