Cell Division

Question 1

what are the essential features of cell division?

Answer 1

• Faithfully replicate genetic material

* Accurately segregate into daughter cells

Question 2

What are the phases of the cell cycle?

Answer 2

G1 Phase

S Phase (DNA Replication)

G2 Phase

M phase

• Mitosis (nuclear division)
• Cytokinesis (cytoplasmic division)

Question 3

What key enzyme controls the phases of the cell cycle?

Answer 3

cyclin dependent kinases (Cdk)

Question 4

Why is the cell cycle called the cell CYCLE?

Answer 4

Cause activity is cyclical

Question 5

What process are the phases of the cell cycle regulated by?

Answer 5

phosphorylation/dephosphorylation

Question 6

How do cyclin-cyclin dependant kinases differentiate between different parts of the cell cycle?

Answer 6

Distinct cyclin:cdk complexes control events in cell division

Question 7

Provide some examples of the distinct cyclin:cdk complexes that control events in cell division

Answer 7

B CDC2 in M phase

D CDK4/6 in G1 up to R point

E CDK2 in G1 phase from R point to start of S phase

A CDK2 from start to midpoint of S phase

A CDC2 from first third of S phase to end of G2

Question 8

Why are accumulation and destruction of certain molecules important in the cell cycle?

Answer 8

Accumulation of certain molecules in the cell are what drives the cell to the next stage of the cell cycle; to prevent unmanaged division these [molecule] must be able to be reduced

Question 9

How is the active cyclin-Cdk complex inactivated?

Answer 9

Through ubiquitylation and then destruction of cyclin leaving inactive Cdk

Question 10

What do the checkpoints in the G1 phase check for?

Answer 10

damaged DNA
and
Unfavourable extracellular environment

Question 11

What does the checkpoint in the S phase check for?

Answer 11

Damaged or incompletely replicated DNA

Question 12

What does the checkpoint in the G2 phase check for?

Answer 12

Damaged or incompletely replicated DNA

Question 13

What does the checkpoint in the M phase check for?

Answer 13

Chromosome improperly attached to the mitotic spindle

Question 14

How do checkpoints prevent cell cycle progression?

Answer 14

Transcription of cyclin dependant kinase (cdk) inhibitors can be induced if conditions are not right for cell division

Question 15

What two things can occur at the R point (or G1/S transition)?

Answer 15

Growth or quiescence

In a non proliferating cell active p16 is present which inhibits expression of S phase genes

In a proliferating cell, p16 is inactive or absent which causes Rb bound to E2F transcription factor to be inactivated and unbind thus allowing for expression of S phase genes

Question 16

How many times in a cell cycle does DNA replication occur?

Answer 16

once

Question 17

How does the cell cycle respond to DNA damage?

Answer 17

• Response depends on stage of cell cycle
• p53- directs transcription of cdk-inhibitors
• CHK2 is activated- inhibits cdc25

Question 18

What are the different stages of DNA replication?

Answer 18

DNA condensation
Forming the spindle
Nuclear envelope breakdown
Chromosomes attach

Metaphase
Anaphase
Cytokinesis
Others, this seems really weird in the lecture slides so write some more notes from a textbook on DNA replication

Prophase
Prometaphase
Metaphase
Anaphase
Interphase
Telophase and
Cytokinesis

Question 19

What occurs due to defects in cohesion in anaphase?

Answer 19

• Roberts Syndrome
• Very rare
• Nature Genetics 37:468- 70

Question 20

What can defects at the spindle checkpoint cause?

Answer 20

Aneuploidy