Phases of the Cell Cycle

Question 1

What are mitogens and during what stage of the cell cycle are they active?

Answer 1

Mitogens are active in the G1 phase. They are the signal to grow and bind to surface of the cell and activate MAPK (mitogen activated protein i.e. Ras) cascade to turn on the Myc Gene and get the cell cycle moving.

Question 2

Myc

Answer 2

Gene that regulates cell cycle. Overexpressed in cancer

Question 3

G1 Phase

Answer 3

Gap Phase 1. It is the longest phase. Purpose is to get bigger.

Question 4

Cellular Conditions in G1

Answer 4

Lots of ATP (need energy to build)
Lots of branched AA
Lots of Glucose
High protein synthesis (synthesis of Licensing Factors)

Question 5

What does mTOR do?

Answer 5

Controls protein production in G1.

Senses Glucose, AA, and GF signals.

Question 6

Rapamycin

Answer 6

Compound that turns off mTOR to stop protein production which stops cell cycling

Question 7

S Phase:

Answer 7

Cell’s entire genome is replicated. Lots of control here.

Question 8

How is DNA synthesis done so quickly?

Answer 8

Lots of Origins of DNA

Question 9

Licensing Factors? What do they do? When are they made, active, and then destroyed??

Answer 9

Made in late G1, active in S, and inhibited Give Origin of Replication “license” to replicate.” by recruiting MCM Helicase

Question 10

Geminin:

Answer 10

Binds to licensing factors and inhibits them. Made in S

Question 11

Cohesins:

Answer 11

Made in S phase. Are the “cage” that holds DNA in place until M phase.

Question 12

G2:

Answer 12

Gap Phase 2. Checks if DNA is made/correct and if cell size is correct.

Question 13

CDKs and Cyclins

Answer 13

Help regulate cell cycle.
Cyclin Dependent Kinase, activated by binding to cyclin. When active phosphorylate the shit out of things.

Cyclins cycle in concentration during cell cycle cuz created and destroyed

Question 14

Cyclin D/3

Answer 14

Binds to CDK4 and CDK6

Promotes passage through G1

Question 15

Cyclin E

Answer 15

Binds to CDK2. Activates S phase.

Question 16

Cyclin A

Answer 16

Binds to CDK2 to continue S Phase

Question 17

Cyclin B

Answer 17

Binds to CDK1 Stimulates M phase

Question 18

Cdc25

Answer 18

dephosphorylates CDK1/Cyclin B so it becomes active. CDK1 can now amplify it’s concentration.

Question 19

Importance of CDK1`

Answer 19

• assembles mitotic spindle
• condenses chromosomes
• breaks down nuclear envelope
• rearranges cytoskeleton

Question 20

4 ways to inhibit Cdks:

Answer 20

1. make no cyclin
2. degrade cyclin
3. inhibitory protein
4. inhibitory phosphorylation

Question 21

Ubiquitin Ligase System

Answer 21

Way to destroy cyclins. via proteosome.

Question 22

SCF

Answer 22

Main Ligase complex Active at G1/S that puts ubiquitin on things and now proteosome eats it.

Question 23

APC/C

Answer 23

Main Ligase Complex at M phase. Separates sister chromatids by:

1st: degrading securin, activating separase
2nd: Separase cleaves cohesin cage

Question 24

G1 Checkpoint with Rb?

Answer 24

Rb protein binds and inhibits transcription.

• Phosphorylated by Cdk4/6 which slightly inhibits it
• Cyclin E/Cdk2 then fully phosphorylate it to turn Rb off, which then ALLOWS TRANSCRIPTION