L25 Cell cycle

Question 1

What three critical events does the cell cycle makes sure happens?

Answer 1

1. Chromosome replication
2. Chromosoem segregation
3. Cell division.

Question 2

How are normal cells stimulated to proliferate?

Answer 2

By extrinsic factors.

Question 3

How can a proliferation be forced to halt?

Answer 3

Overule of stimulatory factors by extracellular signals

Question 4

What is the structure of the cell cycle?

Answer 4

1. G1
2. S Phase.
3. G2
4. Mitosis Phase.

Question 5

What happens in G1 phase?

Answer 5

1. Cell increases in size
2. ribosomes and RNA produced
3. Preparation for DNA synthesis.

Question 6

What happens in S phase?

Answer 6

DNA is synthesised

Question 7

What happens in G2 phase?

Answer 7

1. Cell checks fidelity of DNA
2. Preparation for nuclear division.

Question 8

What are the sub phases of mitosis?

Answer 8

1. Prophase
2. prometaphase
3. metaphase
4. anaphase
5. Telophase.
6. Cytokinesis

Question 9

What is cell - free mitosis?

Answer 9

Technique that allows scientists to study the process of mitosis outside of a living cell

Question 10

How do we isolate the proteins that are responsible for cell cycle transitions?

Answer 10

Frogs eggs grow arrested in G2 to a relatively large size (good for extracting decent amounts of protein)

Oocytes arrested in G2, then under hormonal control mature and start meiosis BUT when they are laid they become stuck in meiotic metaphase ie M-phase. The are released by fertilization to start dividing (without growing)

Question 11

What is maturation promoting factor?

Answer 11

key protein complex in the Egg cytoplasm that can catalyse the transition from G2 to M-phase

Question 12

Look at slide 20

Answer 12

Easy understanding through a picture.

Question 13

How to trigger G2/M transition.

Answer 13

• You can start to take the egg cytoplasm, separate out the proteins into different classes eg by size, etc
• Inject back into an oocyte and see if it triggers the G2 to M transition
• then re-purrify (lane to the right)
• Eventually you get some consistent bands that trigger the G2/M transition
• These bands are similar to the yeast genes identified
• This identified Cyclin-dependent kinases (CDKs) and Cyclins

Question 14

What is G2/M transition?

Answer 14

A cell cycle transition that is controlled by a protein kinase-based machine (AA sequence of CDK)

Question 15

What are protein kinases?

Answer 15

Protein kinases are signaling devices which
operate to create molecular switches

Question 16

How do you visualize and quantify kinase activity?(Talk about procedure)

Answer 16

1. Selective extraction of kinase.
2. Incubation with a protein substrate and ATP.
3. Electrophoresis of substrate and imaging.

Question 17

What does cell cycle transition involve in context to cyclins?

Answer 17

Cell cycle transitions involve the irreversible destruction of cyclins

Question 18

How many cell cycle regualator kinase gene are there and what are they in yeast?

Answer 18

In yeast, there is only ONE cell cycle regulator kinase gene, called Cdk1. However, there are multiple cyclins.

Question 19

How many cell cycle regualator kinase gene are there and what are they in mammals?

Answer 19

In mammals , there are multiple Cdks as well as multiple cyclins.

Question 20

Explain the fluctuation of cyclin levels during cell cycle?

Answer 20

Cyclin E: low levels throughout most of G1, rapid increase after the R point
Cyclin A: levels increase in concert with the entrance in S phase
Cyclin B: levels increase in anticipation of mitosis

Collapse of cyclin levels as the cell progresses through the cell cycle  degradation (ubiquitination-dependent)

Question 21

Can cell cell cycle progress in more than one direction?

Answer 21

No, The cell cycle can only progress in one direction.