Cell Bio Lecture 8: Cell Birth and Death Pt. 2

Question 1

What percentage of a person’s cells are in G0 phase?

Answer 1

99.9%

Question 2

In what cell cycle is the R point? Do cells that enter G0 have to go through the R point again?

Answer 2

G1. When G0 cells come out of G0 they DO have to go through the R point again.

Question 3

What is MPF?

Answer 3

Meiosis/mitosis promoting factor. AKA Cyclin B/cdk1

Question 4

Which cyclin is the mitotic cyclin?

Answer 4

Cyclin B

Question 5

What makes for an active mitotic-cdk complex?

Answer 5

Binding of the cdk to cyclin does not make for an activated complex. The complex is phosphorylated twice (one activates, one deactivates - and the deactivating P dominates). Once an activating phosphatase removes the deactivating phosphate, the active P remains and the complex is now activated.

Question 6

Which cyclin is in the G1 phase and what is/are its cdk partner(s)?

Answer 6

Cyclin D - Cdk 4 or 6

Question 7

Which cyclin is in the G1/S phase and what is/are its cdk partner(s)?

Answer 7

Cyclin E - Cdk 2

Question 8

Which cyclin is in the S phase and what is/are its cdk partner(s)?

Answer 8

Cyclin A - Cdk 2

Question 9

Which cyclin is in the M phase and what is/are its cdk partner(s)?

Answer 9

Cyclin B - Cdk 1

Question 10

From whom was Rb protein first isolated from?

Answer 10

Retinoblastoma patients

Question 11

Which Cyclins drive the cell through the R point? How?

Answer 11

Cyclins D and E inactivate Rb protein by phosphorylating it, forcing its withdrawl from inhibitory binding of the transcription factors.

Question 12

What is Rb protein’s role in transcription?

Answer 12

A phosphorylated Rb protein binds to transcription factors to block transcription.

Question 13

What is the mutated ErbB receptor an example of? What happens with a mutated ErbB receptor?

Answer 13

It is an example of neoplasia (or tissue field theory of carcinogenesis). A mutated receptor fires its transduction signal even without its ligand (EGF growth factor). It was one of the first oncogenes discovered.

Question 14

What are the characteristics of necrosis?

Answer 14

1. It is accidental cell death
2. Triggered by sustained ischemia, physical or chemical trauma
3. Cells swell, organelles damaged, chromatin is RANDOMLY degraded
4. Cells lyse, organelles are destroyed
5. It leads to inflammation (recruitment of polynuclear leukocytes and macrophages)

Question 15

What are the characteristics of apoptosis?

Answer 15

1. It is programmed cell death
2. Cells shrink, organelles intact, chromatin is degraded systematically
3. Membrane blebs, cell contents retained in blebs.
4. Leads to phagocytosis

Question 16

What is polycystic kidney disease an example of?

Answer 16

Too much apoptosis.

Question 17

Describe the DNA ladder. What is it a characteristic of?

Answer 17

The DNA ladder is what a DNA gel looks like when a cell is undergoing apoptosis. The steps in the ladder correspond to where endonucleases cleave DNA between nucleosomes at the linkers (~180 bps).

Question 18

What are two key substrates for cyclinB-cdk1 complexes?

Answer 18

Lamins and histones.