Week 12: Cell Cycle Control

Question 1

how is the cell cycle regulated

Answer 1

cell signalling

checkpoints have to be met

a cell can halt the cell cycle if it doesnt meet the checkpoints

Question 2

Mitogens

Answer 2

stimulate cell division by overcoming cell cycle “brake” that leads to G0

Question 3

growth factors

Answer 3

stimulate growth (increased cell size) by promoting synthesis & inhibiting degradation of macromolecules

Question 4

Survival factors

Answer 4

suppress apoptosis (programmed cell death)

Question 5

what is the g1 checkpoint

Answer 5

is the environment favorable

Question 6

what is the g2 checkpoint

Answer 6

is all DNA replicated and damage repaired

Question 7

what is the checkpoint in mitosis in metaphase

Answer 7

are all chromosomes properly attached to the mitotic spindle

Question 8

what is the role cyclin-dependent kinases

Answer 8

responsible for regulating the cell cycle

Question 9

What do cyclin-dependent kinases do

Answer 9

Cdks are inactive unless bound to another protein, a cyclin

When active, Cdks phosphorylate & activate numerous other proteins involved in regulating the cell cycle

Question 10

What is the activity of cyclins

Answer 10

Cdk’s are present in the cell throughout the cell cycle

need to be bound to a cyclin

Different cyclin-Cdk complexes trigger different steps in the cell cycle

Concentration of Cdk does not change – just it’s activity

eg. M-Cyclin concentration increases during interphase & falls during mitosis - it’s role is to activate M-Cdk, which then triggers mitosis

Question 11

What does M-Cdk do

Answer 11

M-cyclin + mitotic Cdk = M-Cdk (M-cyclin/Cdk complex)

Phosphorylates & activates key proteins that:

1. cause chromosomes to condense
2. cause the nuclear envelope to break down
3. cause the formation of the mitotic spindle

entry into M phase

Question 12

S-CDKs

Answer 12

transition to S-phase

S-Cdks activate proteins that

1. recruit DNA polymerase to replication points on chromosomes
2. triggering DNA replication

Question 13

CDKs and Cancer

Answer 13

Mutations in Cdks & cyclins are common in cancer cells

These mutations allow a cell to progress through the cell cycle without the normal checks
increasing the chance that a cell with potentially cancerous mutations divides

Cancer is a complex group of disorders in which cells survive, grow, and divide when they should not. ie uncontrollably

The mechanisms controlling normal cell division do to work effectively, due to DNA mutations

Question 14

Somatic cells

Answer 14

sporadic cancer only affecting the individual

Question 15

Germline cells

Answer 15

mutations are inherited

Question 16

characteristics of cancer cells

Answer 16

1. Divide continually (given space & nutrients)
2. Have heritable mutations: cells with mutations have daughter cells which inherit the same mutations
3. Transplantable
4. Dedifferentiated: cells lose their specialised identity
5. Different appearance: reflects dedifferentiation
6. Lack contact inhibition: will divide in a crowd of cells and pile on top of each other
7. Induce angiogenesis (local blood vessel formation)
8. Show an increased mutation rate
9. Invasive: squeeze into any space available
10. Metastasize: cells move to new location in the body

Question 17

oncogenes “accelerate”

Answer 17

Causes expression of protein in the wrong quantity, at the wrong time or in the wrong cell type leading to uncontrollable cell division & cancer
e.g. genes encoding for kinases, growth factors, transcription factors

Question 18

tumour supressor genes “brake”

Answer 18

uncontrolled cell proliferation, leading to uncontrollable cell division and cancer

e.g. genes coding for cell cycle checkpoint proteins

Question 19

Cell death

Answer 19

apoptosis

necrosis

Question 20

Apoptosis

Answer 20

programmed cell death
Controlled, cell contents are not released
Cellular suicide, no inflammation
Determined by activity anti-apoptotic proteins vs pro-apoptotic proteins and activation of caspase enzymes which allows careful dismantling of cell components

Question 21

necrosis

Answer 21

Uncontrolled, cell contents are released

Cellular injury, leads to inflammation

Question 22

why do cells undergo cell death

Answer 22

Needed to destroy cells that represent a threat to the integrity of the organism

Cells with DNA damage
Cells infected with viruses
Cells of the immune system
Cancer cells