Cell cycle and its control

Question 1

Almost all normal cells won’t proliferate unless stimulated by what, and what can overrule them?

Answer 1

-extrinsic factors
-other signalling factors can overrule them

Question 2

What 4 phases make up the cell cycle and what happens in each?

Answer 2

-M phase - replicated DNA is separated + cytokinesis
-S phase - DNA replication
-G1 phase - gap between M phase + S phase
-G2 phase - gap between S phase + M phase

Question 3

Which phases make up interphase?

Answer 3

All but M phase

Question 4

What occurs in M phase?

Answer 4

-prophase
-prometaphase
-metaphase
-anaphase
-telophase
-cytokinesis

Question 5

What happens in prophase?

Answer 5

Movement of centrioles to polar ends of nucleus + chromosome condensation

Question 6

What happens during prometaphase and metaphase?

Answer 6

-pro = components of mitotic spindle elongate away from spindle poles
-met = chromosome pair alignment is completed

Question 7

What happens in anaphase and telophase?

Answer 7

-ana = pairs of sister chromatids separate
-tel = chromosomes decondense + nuclear membrane is re-established

Question 8

What happens during G1 phase in interphase?

Answer 8

-preparation for DNA synthesis
-cells increase in size
-ribosomes RNA produced

Question 9

What happens during S phase in interphase?

Answer 9

-DNA synthesised
-chromosomes are duplicated

Question 10

What happens during G2 phase in interphase?

Answer 10

-preparation for nuclear division
-cells check fidelity of DNA

Question 11

What do cells enter if they exit the G1 phase?

Answer 11

-enter G0 phase
-won’t divide or grow in this phase
-can re-enter the cell cycle

Question 12

What allows cells to exit the G1 phase and enter the G0 phase?

Answer 12

-they consult the extracellular environment
-if environment not right, they can exit the cell cycle

Question 13

At what points can growth factors be removed in G1 phase to determine what phase the cell enters next?

Answer 13

-removed before R point - don’t proceed + go to phase G0
-removed after R point - proceed to S, G2 + M phase

Question 14

What can dysregulation of R point decision making lead to?

Answer 14

Formation of most types of cancer

Question 15

Describe the genetic approach to investigating the genes responsible for cell cycle transitions

Answer 15

-requires cells that have a mutation in an already accepted cell cycle transition gene
-if mutation stops cell cycle, then stops cells from proliferating

Question 16

Why is yeast used as a genetic model?

Answer 16

-rapid division rate
-cell cycle control genes are highly conserved
-yeast can grow as haploids or diploids
-easy to grow
-can tell which phase of cell cycle the cell is in just by looking at it

Question 17

Describe the biochemical approach to investigating the genes responsible for cell cycle transitions

Answer 17

-use toads
-oocytes grow without dividing + become arrested in G2
-eventually divide + transition into M phase, where they become arrested again
-when fertilised, released from M phase + division occurs without cells changing size until tadpole produced
-something in egg cytoplasm can catalyse transition from G2 to M phase - maturation promoting factor (MPF)

Question 18

What controls the G2 phase to M phase transition?

Answer 18

Mutations in certain genes that control the phases lead to identification of CDK genes + cyclins

Question 19

When active, what do cyclins and CDKs exist as?

Answer 19

Complexes

Question 20

How do you quantify kinase activity?

Answer 20

-selective extraction of kinase
-incubation with a protein substrate + ATP
-electrophoresis of substrate + imaging

Question 21

What is the difference in CKS and cyclins between yeast and mammals?

Answer 21

-in yeast, only 1 CDK gene (CDK1) + multiple cyclins
-in humans, multiple CDKs + multiple cyclins

Question 22

Describe the levels of cyclins E, A and B throughout the cell cycle

Answer 22

-E = low levels through most of G1, rapid increase after R point
-A = levels increase with entrance to S phase
-B = levels increase in anticipation of mitosis

Question 23

What does the levels of cyclin decreasing as the cell progresses through the cycle ensure?

Answer 23

The cell cycle can only progress in 1 direction