6.1 The Cell Cycle

Question 1

What happens in interphase ?

Answer 1

DNA is replicated and checked for errors in the nucleus

Protein synthesis occurs in the cytoplasm

Mitochondria grow and divide, increasing in number

Chloroplasts grow and divide, increasing in number

Normal metabolic processes of cells occur

Question 2

Name the three stages of interphase. What happens at each stage?

Answer 2

G1 : first growth phase - protein synthesis and organelles replicate. Cell increases in size.

S : synthesis phase - DNA replication in nucleus

G2 : second growth phase - cell continues to increase is size, energy stores ( mitochondria ) increased, DNA checked for errors

Question 3

What are the two phase of cell division ?

Answer 3

Mitosis : nucleus divides

Cytokines : cytoplasm divides and two cells produced

Question 4

What is G0?

Answer 4

Phase when cell leaves the cycle ( temporary or permanent )

Question 5

What are the reasons for G0?

Answer 5

Differentiation : a cell that is specialised to a particular function can no longer divide.

DNA may be damaged, and therefore the cell cannot divide. This is called being senescent.

Growing numbers of senescent cells have been linked with many age related diseases, such as cancer and arthritis.

Question 6

What are checkpoints ?

Answer 6

Control mechanisms of the cell cycle.

They monitor and verify wether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress to the next phase.

Question 7

Where are the different checkpoints ?

Answer 7

G1 checkpoint : end of g1, before S. check for :

Cell size
Nutrients
Growth factors
DNA damage

G2 checkpoint : end of g2, before mitotic phase. Check for :

Cell size
DNA replication
DNA damage

Spindle assembly checkpoint : check that :
All chromosomes should be attached to spindles and have aligned.