theme 3-CB 16 Cell cycle and cell division

Question 1

define the cell cycle

Answer 1

The cycle of duplication and
division (co-ordinated) that is undertaken to replicate the
cell and its contents

Question 2

Why is the cell cycle important:

Answer 2

Fundamental to growth and

development of the organism

Question 3

What is the relationship between the cell cycle and cell devision

Answer 3

cell division in M phase of the cell cycle

Question 4

What are the main events of the cell cycle:

Answer 4

1) M phase
2) G1 phase
3) S phase
4) G2 phase

Question 5

Describe G1 phase during interpase:

Answer 5

gap

Question 6

Describe S phase during interpase:

Answer 6

DNA replication

Question 7

Describe G2 phase during interpase:

Answer 7

gap

Question 8

What happens in M phase in the cell cycle:

Answer 8

mitosis and cytokinese

Question 9

what happens in prophase?

Answer 9

• chromosome condensation
• formation of spindle apparatus
• nuclear envelope breaks down
• spindle attaches to centromeres (kinetochore)

Question 10

What happens in metaphase?

Answer 10

-chromosomes align at equator (using motor protiens and microtubules)

Question 11

What happens in anaphase?

Answer 11

-sister chromatids pulled apart

Question 12

What happens in telophase?

Answer 12

• nuclear envelope reforms
• cytokinesis (contractile ring (actin and myosin filaments , cyoplasm divides)
• chromosomes unravel

Question 13

What are proteasomes?

Answer 13

protein complexes which degrade unneeded or damaged proteins by proteolysis

Question 14

What do activated cyclin dependent kinases?

Answer 14

turns biochemical switches that act in a sequence on (by phosphorylation) and off (by dephosphorylation) which allows synthesis of new components as well as partition and division process to be regulated.

Question 15

What do activated cyclin dependent kinases?

Answer 15

turns biochemical switches that act in a sequence on (by phosphorylation) and off (by dephosphorylation) which allows synthesis of new components as well as partition and division process to be regulated.

Question 16

How are cyclin-dependent kinases activated?

Answer 16

mitogens causes accumulation of a particular cyclin at the appropriate time during the cell cycle.

1) cyclin binds to cdk= cyclin-cdk complex
2) protein kinases phosphorylate complex, one phosphate is activating and one in inhibiting, the inhibiting phosphate is expressed.
3) Activating protein phosphatase desphosphorylates complex, removing inhibiting phosphate= activated cyclin-cdk complex.

Question 17

How is a particular cyclin-cdk switched off?

Answer 17

1) cyclin is ubiquitylated by anaphase promoting complex (APC)
2) Marks it for destruction
3) proteosomes degrade cyclin, breaking up complex

Question 18

How is a particular cyclin-cdk switched off?

Answer 18

1) cyclin is ubiquitylated by anaphase promoting complex (APC)
2) Marks it for destruction
3) proteosomes degrade cyclin, breaking up complex

Question 19

How do cells move through the cell cycle?

Answer 19

through a series of checkpoints, at each checkpoint, a particular cdk must be activated then deactivated through phosphorylation and dephosphorylation reactions.

Question 20

What stops the cell cycle? +e.g.

Answer 20

through the synthesis of cdk inhibitor proteins, like p21, that bind to cyclin-cdk complexes and inactivate them.

Question 21

Describe what would occur after DNA damage is noticed by the cell?

Answer 21

1) protein kinases would be activated and phosphorylate p53, a protein being synthesised by the cell all the time
2) The phosphorylation of p53 makes it stable (so isn’t degraded in proteosomes like it normally is) and activated.
3) activated p53 binds to regulatory region = transcription of p21 gene
4) p21 is synthesised
5) p21 binds to active cyclin-cdk complex = stops its function

Question 22

What 2 things can occur after p21 has bound to cyclin-cdk complex?

Answer 22

1) DNA repaired, p21 releases complex

2) DNA unable to be repaired= cell apoptosis

Question 23

What percentage of cancers are caused by a mutation in p53 gene?
Why does it cause cancer?

Answer 23

50%
mutation means DNA doesn’t have time to be repaired if other mutations occur, and cell apoptosis cannot occur= uncontrolled cell growth