Cell Cycle

Question 1

What is the principal role of the cell cycle?

Answer 1

To produce two genetically identical daughter cells?

Question 2

Why are the gap phases necessary?

Answer 2

Need to grow in-between divisions otherwise cells would get smaller over time

Question 3

What are the two main phases of the cell cycle?

Answer 3

Interphase and mitosis

Question 4

What are the 3 subphases of interphase?

Answer 4

G1 - Gap phase
S - Synthesis phase
G2 - Gap phase 2

Question 5

What is G0?

Answer 5

A non-dividing, differentiated state

Question 6

Which phase are most human cells in?

Answer 6

G0

Question 7

Example of cells in G0

Answer 7

Liver cells, but can be ‘called back’ into the cell cycle

Question 8

Which cells are ‘arrested’ in G0?

Answer 8

Nerve and muscle cells

Question 9

What occurs during the gap phases?

Answer 9

Cell checks and growth

Question 10

What occurs during the synthesis phase?

Answer 10

DNA replication

Question 11

What occurs during M phase?

Answer 11

Nuclear and cytoplasmic division

Question 12

Stages of mitosis

Answer 12

Prophase
Prometaphase
Metaphase
Anaphase
Telophase
(cytokinesis)

Question 13

What occurs during prophase?

Answer 13

• Sister chromatids condense

- Mitotic spindle assembles between two centrosomes that have moved apart

Question 14

What occurs during pro metaphase?

Answer 14

• Nuclear envelope breaks down
• Chromosomes attached to spindle microtubule via their kinetochores
• Movement of chromosomes begin

Question 15

What occurs during metaphase?

Answer 15

• Chromosomes assemble along the equator

- Kinetochore microtubules attach sister chromatids to opposite poles of the spindle

Question 16

What occurs during anaphase?

Answer 16

• Sister chromatids separate to form two daughter chromosomes –> each pulled towards spindle pole
• Kinetochore microtubules shorten by depolymerisation at their kinetochore ends and spindle poles move apart

Question 17

What occurs during telophase?

Answer 17

• Two sets of daughter chromosomes arrive at the spindle poles and decondense
• Nuclear envelopes form around each set to produce two nuclei

Question 18

What is cytokinesis?

Answer 18

Cytoplasm is divided by a contractile ring of actin and myosin filaments to form two cells from one

Question 19

What are the three classes of microtubules involved in mitosis?

Answer 19

• Astral: help to position the spindle correctly
• Interpolar: help to stabilise the interpolate spindle
• Kinetochore: help separate the sister chromatids

Question 20

When is the main checkpoint in the cell cycle?

Answer 20

Metaphase
-If chromosomes don’t pair up –> negative signal released
- all attached –> positive signal
nature of signals: phosphorylation and preoteolysis

Question 21

What is the nature of the signals that are released at checkpoints?

Answer 21

Phosphorylation and proteolysis

Question 22

In Xenopus, what is the cell cycle regulated by?

Answer 22

Cyclin-dependent kinases (Cdk)

Question 23

What does Cdk require for activity?

Answer 23

Cyclin

Question 24

What is Cdk further regulated by?

Answer 24

Phosphorylation/Dephosphorylation

Question 25

Is the level of cyclin constant throughout the cell cycle?

Answer 25

No, they are synthesised and degraded throughout

Question 26

Is the level of Cdk constant through the cell cycle?

Answer 26

Yes, relatively

Question 27

What are cyclin levels regulated by?

Answer 27

The anaphase-promoting complex

Question 28

What controls the metaphase-anaphase transition?

Answer 28

Proteolysis