Cell Cycle

Question 1

What are the life expectancy of RBCs?
Phagocytes?
B-lymphocytes?
Skin?
Intestinal epithelial cells?

Answer 1

RBCs - 120 days
Phagocytes - 90 days
B-Lymphocytes - years
Skin - 3-4 weeks
Intestinal epithelial cells - 4 days

Question 2

What are the stages of the cell cycle?

Answer 2

G1, S, G2, Mitosis, Cytokinesis

G0 = after G1 (arrest)

Question 3

What are the cyclins?

Answer 3

A group of enzymes which control cell cycle progression (kinases)

Question 4

What does E2F do?

Answer 4

Transription factor which regulates S phase genome replication. Becomes active when Retinoblastoma (Rb) is phosphorylated = released from complex

Question 5

What are the 4 major cyclins?

Answer 5

Cyclin D - E2F control (G1)
Cyclin E - E2F control (G1)
Cyclin A (S)
Cyclin B (G2)

Question 6

What are the stages of mitosis?

Answer 6

Prophase - Chromosomes start condensing. Spindle fibres are formed
Prometaphase - Chromosomes attach to spindle fibres
Metaphase - Chromosomes start to align in the centre
Anaphase - Sister chromatids move to opposite poles
Telophase - Chromatids decondense. Spindle fibres dissolve
Cytokinesis - Cytoplasm divides. New cell formed

Question 7

What is the structure of a chromosome?

Answer 7

Short arm, Centromere (kinetochore for spindle fibre binding), Long arm (telomeres to prevent reduction of genome upon replication)

Question 8

How do the sister chromatids migrate to the poles?

Answer 8

Move along the spindle fibres towards the microtubule organising centres. Polar microtubules attract the chromatid while the K fibres allow movement

Question 9

What happens in meiosis?

Answer 9

Mitosis happens twice (effectively)

4 haploid genomes generated (23 chromosomes each not 46)

Question 10

How is genetic diversity maintained?

Answer 10

Crossing over of chromatids