6.1 The Cell Cycle

Question 1

Cell cycle

Answer 1

Highly ordered sequence of events that takes place in a cell, causing division and formation of 2 genetically identical daughter cells

Question 2

Interphase

Answer 2

Long periods of growth and normal working

No active dividing takes place

Question 3

What happens during interphase?

Answer 3

DNA replication and checking for errors in the nucleus
Protein synthesis in the cytoplasm
Mitochondria grow and divide - increase number in cytoplasm
Chloroplasts grow and divide in plant and algae
Normal metabolic processes of cells occur

Question 4

3 phases of interphase

Answer 4

G1
S
G2

Question 5

What happens during the G1 phase?

Answer 5

First growth phase
Proteins from which organelles are synthesised are produced and organelles replicate
Cell increases in size

Question 6

What happens during the S phase?

Answer 6

Synthesis phase

DNA is replicated in the nucleus

Question 7

What happens during the G2 phase?

Answer 7

Second growth phase
Cell continues to increase in size
Energy stores are increased
Duplicated DNA is checked for errors

Question 8

2 stages of mitotic phase

Answer 8

Mitosis

Cytokinesis

Question 9

G0 phase

Answer 9

When cell leaves the cycle - temporarily or permanently

Question 10

Reasons for a cell entering G0 phase

Answer 10

Differentiation - cell that becomes specialised for a function cannot divide any more - will not enter cell cycle again
DNA is damaged - no longer viable, can no longer divide and enters permanent cell arrest
As we age, number of senescent cells increase (cells only divide a limited number of times)

Question 11

Cells that can enter cell cycle again after G0

Answer 11

Lymphocytes, during an immune response

Question 12

What are checkpoints?

Answer 12

Control mechanisms of the cell cycle
Monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed into the next phase

Question 13

Different checkpoints in cell cycle

Answer 13

G1 checkpoint
G2 checkpoint
Spindle assembly checkpoint

Question 14

G1 checkpoint

Answer 14

End of G1 phase, before entering S phase
If cell satisfies requirements, DNA replication starts
If not, it enters resting state

Question 15

G2 checkpoint

Answer 15

End of G2 phase, before start of mitotic phase

DNA replication must be done without error - if passed, mitosis begins

Question 16

Spindle assembly checkpoint

Answer 16

AKA metaphase checkpoint
Where all chromosomes should be attached to spindles and have aligned
Mitosis cannot proceed until this has happened

Question 17

What controls the passing of a cell cycle checkpoint?

Answer 17

Kinases

Question 18

What are kinases?

Answer 18

Class of enzyme that catalyse addition of phosphate group to protein - phosphorylation

Question 19

How are kinases activated during cell cycle regulation?

Answer 19

By binding to a variety of checkpoint proteins called cyclins
This forms a cyclin dependent kinase complex (CDK)

Question 20

How can cancer arise?

Answer 20

Over expression of a cyclin gene from mutation
Large number of cyclins produced disrupt regulation of cell cycle
This causes uncontrollable cell division and tumour formation