The Cell Cycle

Question 1

What is the purpose of the cell cycle control system?

Answer 1

It is used to control the sequence and timing of the different parts of the cell cycle

Question 2

What is the first transition point of the cell cycle and what happens during it?

Answer 2

1) G1 to S-confirms environment is favorable for proliferation
A) animals need sufficient nutrients
B) & specific signals molecules in extracellular fluid
C) if unfavorable, Cell will delay replication or enter a rest stage(G0 Stage)
D) signals from other cells stimulate or block cell proliferation

Question 3

What is the 2nd transition point of the cell cycle and what happens during it?

Answer 3

2) G2 to M

Confirms DNA is undamaged and intact after replication

Question 4

What is the 3rd transition point of the cell cycle and what happens during it

Answer 4

3) Metaphase to Anaphase

Ensure spindle fibers are attached to chromosomes before pulling apart

Question 5

What do animal cells need to transition to G1 to S

Answer 5

They need sufficient nutrients and specific signal molecules in extra cellular fluid

Question 6

What is extracellular fluid

Answer 6

It denotes all body fluid outside the cells

Question 7

What does G0 entail

Answer 7

It is a resting stage. Here the cell is not preparing to divide

Question 8

What is another name for spindle fibers

Answer 8

Mitotic Spindles

Question 9

What are the two types of machinery in the cell cycle

Answer 9

1) Manufactures new components of growing cell

2) Moves components to correct locations and isolates them during division

Question 10

What is the connection between the cell cycle control System and the machinery

Answer 10

The cell cycle control system switches this machinery on and off at the appropriate times

Question 11

What is the chemistry of activating or deactivating proteins or protein complexes

Answer 11

The chemistry is that it is through phosphorylation and dephosphorylation

Question 12

What is phosphorylation

Answer 12

Controlled by protein kinases

- activated at specific times in the cell cycle
 - activation is regulated by cycling
 - complex is called Cyclin-dependent protein    kinases(Cdks)

Question 13

What are protein kinases

Answer 13

An enzyme that catalyze the transfer of PO4 to a different compound(substrate)

Question 14

What does it mean to substrate?

Answer 14

Compound that you add the phosphate to

Question 15

What protein is used to regulate protein kinases

Answer 15

Cyclins

Question 16

What are cyclins

Answer 16

Proteins that bind to kinases to activate them

Question 17

What are the 4 types of Cdk’s?

Answer 17

M - Cdk
S - Cdk
G1/S - Cdk
G1 - Cdk

Question 18

What is the function of this M Cdk

Answer 18

Triggers entry into M phase(Mitosis)

Question 19

What is the function of the S Cdk & G1/S Cdk

Answer 19

Starts S phase (replication)

Question 20

What is the function of the G1 Cdk

Answer 20

Moves Cell through G1 (growth)

Question 21

How is the concentration of Cyclin controlled

Answer 21

It is regulated by transcription and proteolysis

• the gradual increase in the concentration is due to increased transcription of cyclin gene
  - Abrupt decrease is due to concentrated destruction of protein(proteolysis)

Question 22

What are the three places the cell cycle control system can pause the cell cycle

Answer 22

1) G1 to S transition
2) G2 to M transition
3) End of Mitosis

Question 23

What happens when the G1 to S transition pauses the cell cycle

Answer 23

They use Cdk inhibitors to keep the cell out of S phase and DNA replication

Question 24

What happens when the G2 to M transition pauses the cell cycle

Answer 24

An inhibitory kinase is used to inactivate the complex

Question 25

What happens at the end of Mitosis and it pauses the cell cycle

Answer 25

Inhibits APC(anaphase-promoting complex) which tags the complex for destruction

If the complex isn’t destroyed , cell doesn’t enter anaphase

Question 26

What happens if the cyclin-Cdk complexes aren’t stopped at the end of Mphase

Answer 26

If it is not disabled, the cell hoes right back into Mitosis with no growth

Question 27

What are the 3 mechanics to neutralize cyclin-Cdk complexes

Answer 27

1) Eliminating all existing cyclins
- a ubiquitin chain is added to the cyclin
- ubiquitin is recognized by a complex called a proteasome
- Proteasome’s have many protease in them, which chop up the protein that was tagged
2) blocking the formation of new cyclins
3) deploying Cdk inhibitor proteins

Question 28

Explain two ways cells can prevent Cdk’s from preforming their job

Answer 28

They are blocked by Cdk inhibitor Proteins by either blocking the assembly or blocking the activity of cyclin Cdk complex

Question 29

List 2 ways other cells can influence cell proliferation

Answer 29

1) needs sufficient Nutrients

2) specific signals molecules in extracellular Fluid

Question 30

Even though Cdk’s concentration slowly increase,

Answer 30

They turn on abruptly

Question 31

Why do cells prevent Cdks from working immediately?

Answer 31

It is due to inhibitory phosphates (added when the complex forms)

Question 32

What cells activate all the Cdk’s at once?

Answer 32

Phosphates are removed by a protein phosphatase which makes them active