G0 and control of the cell cycle

Question 1

What are the two stages of the mitotic phase?

Answer 1

mitosis - nucleus divides

cytokinesis - cytoplasm divides and two cells are produced

Question 2

What is G0?

Answer 2

the name given to the phase when the cell leaves the cycle either temporarily or permanently

Question 3

What are the reasons for G0?

Answer 3

differentiation - a cell that becomes specialised is no longer able to divide

damaged DNA - cell is no longer viable, centers a period of permanent cell arrest.

normal cells only divide a limited number of time and eventually become senescent

the number of senescent cells have been linked with cancer and arthritis

Question 4

When can cells leave G0?

Answer 4

some types can be stimulated to go back into the cell cycle and start dividing

e.g. lymphocytes in an immune response

Question 5

Why does division need to be controlled?

Answer 5

to ensure the cell only divides when it has grown to the right size

to ensure the replicated DNA is error-free

to check chromosomes are in their correct position

to ensure that the two daughter cells are identical to the parent cell

Question 6

What are checkpoints?

Answer 6

control mechanisms of the cell cycle

they monitor and verify whether the processes at each phase of the cell cycle have been accurately completed

if the cell cannot pass the checkpoint it will enter G0

Question 7

What does the G1 checkpoint verify?

Answer 7

must pass G1 checkpoint before entering S

checks for cell size, nutrients, growth factors and DNA damage

Question 8

What does the G2 checkpoint verify?

Answer 8

before the start of the mitotic phase

checks if DNA has been replicated correctly

also checks for cell size and DNA damage

Question 9

What is the function of the spindle assembly checkpoint?

Answer 9

checks all chromosomes attached to the spindles and are orientated correctly

mitosis cannot proceed until this checkpoint is passed