Cell cycle

Question 1

What is the cell cycle?

Answer 1

Orderly sequence of events where a cell duplicates its contents and divides in two

Question 2

What is the most vulnerable period of the cell cycle?

Answer 2

Mitosis:
cells can be easily killed
DNA damage cannot be repaired
Gene transcription silenced

Question 3

What are the different stages of the cell cycle?

Answer 3

M phase - mitosis
Interphase:
G0, G1, S, G2

Question 4

What occurs during the S phase of interphase?

Answer 4

DNA replication occurs:

• Protein synthesis: initiation of translation and elongation increased
• Replication of organelles

Question 5

What is a centrosome and what are their functions?

Answer 5

An organelle consisting of two centrioles, which are made up of barrels of nine triplet microtubules
They are used as a microtubule organising centre and form mitotic spindles

Question 6

What are the 6 phases of mitosis?

Answer 6

Prophase, Prometaphase, Metaphase, Anaphase, Telophase, Cytokinesis

Question 7

What occurs during prophase 1?

Answer 7

Chromatin is condensed, replicated chromosom

Question 8

What is a kinetochore?

Answer 8

A structure which holds 2 sister chromatids together at their centromere

Question 9

What occurs during prophase 2?

Answer 9

1. Replicated chromosomes condense
2. Duplicated centrosomes migrate to opposite sides of the nucleus and organise the assembly of microtubules
3. Mitotic spindle forms outside the nucleus between the 2 centrosomes

Question 10

What occurs to produce spindle formation?

Answer 10

1. Radial microtubule arrays from around each centrosome
2. Radial arrays meet
3. Polar microtubules form

Question 11

What occurs during prometaphase 1?

Answer 11

1. Breakdown of the nuclear membrane
2. Spindle formation largely complete
3. Attachment of chromosomes to spindle via kinetochores

Question 12

What occurs during prometaphase 2?

Answer 12

1. Microtubule from opposite pole is captured by sister kinetochore
2. Chromosomes attached to each pole congress to the middle
3. Chromosomes slides rapidly towards centre along microtubules

Question 13

What occurs during anaphase A?

Answer 13

1. Breakdown of cohesin
2. Microtubules get shorter
3. Daughter chromosomes pulled to opposite spindle poles

Question 14

What occurs during anaphase B?

Answer 14

1. Daughter chromosomes migrate towards poles

2. Spindle poles (centrosomes) migrate apart

Question 15

What occurs during telophase?

Answer 15

1. Daughter chromosomes arrive at spindle
2. Nuclear envelope reassembles at poles
3. Assembly of contractile ring

Question 16

What occurs during cytokinesis?

Answer 16

Contractile ring contracts and a midbody forms and a new membrane is inserted and 2 daughter cells are produced
Chromatin condenses, nuclear membrane forms

Question 17

What 2 things can occur when something goes wrong during the cell cycle?

Answer 17

1. Cell apoptosis:
   DNA damage too great
   Chromosomal abnormalities
   Toxic agents
2. Cell cycle arrest - cell is not involved in processes involving duplication and division:
   at check points (G1 and spindle check point)
   Can be temporary (i.e. following DNA repair)

Question 18

What triggers a cell to enter the cycle and divide?

Answer 18

• In the absence of stimulus, cell go into G0
• Most cells in the body which are differentiated to perform specific functions
• Cells are not dormant, but are non dividing