Lecture 12 Cell cycle and death

Question 1

the cell cycle

Answer 1

1. cell growth and chromosome replication
2. chromosome segregation
3. cell division

Question 2

interphase

M phase

Answer 2

interphase: G1, S, M

M phase: mitosis + cytokinesis

Question 3

mitosis

Answer 3

prophase metaphase anaphase telophase

Question 4

control systems of the cell cycle

Answer 4

3 major regulatory checkpoints:

Start = restriction point: in the late G1, cell commits to chromosome duplication

G 2/M point: system triggers chromosome alignment

metaphase-to-anaphase transition: system stimulates chromatide separation and pushes to the completion of the cycle and initiation of cytokinesis

Question 5

the cyclins

Answer 5

• G1/S cyclins trigger progression through start point
• S cyclins trigger DNA replication
• M-cyclins trigger mitosis
• APC/C complex triggers anaphase

Question 6

each cyclin activates specific cyclin-dependent protein …

Answer 6

kinases

Question 7

The level of Cdks is constant (constitutive) in the cell, but the level of … change.

Answer 7

cyclins

Question 8

The oscillation in levels of cyclins (synthesis and degradation) is the main mechanism for regulating the Cdks activity, but not the only one. Other important mechanisms are also involved:

Answer 8

• phosphorylation of the cyclin-Cdk complex by the kinase Wee1 inhibits its kinase activity
• dephosphorylation of the same residues by the phosphatase Cdc25 increases the activity
• binding of Cdk inhibitor proteins (e.g. p27) to the complex rearranges the active site of the kinase and renders it inactive

Question 9

Onset of mitosis depends mainly on the protein kinase M-Cdk. When activated, M-Cdk activates the following processes:

Answer 9

• induction of assembly of mitotic spindle
• attachment of sister chromatides to the opposite poles of the spindle
• chromosome condensation
• breakdown of nuclear envelope
• rearrangement of actin cytoskeleton and Golgi apparatus

Question 10

activation of M-Cdk

Answer 10

M-cyclin gradually accumulated in the cell
Cdk1 in complex with M-cyclin gets phosphorylated by CAK, catalyzed by Wee1
inactive complex building up
Phosphatase Cdc25 removes the inhibitory phosphate
-> M-Cdk complex active
+ two positive feedback loops

Question 11

M -Cdk initiates the spindle assembly in …

Answer 11

Prophase

Question 12

Spindle attaches to … on chromosomes

Answer 12

kinetochore

Question 13

prophase

Answer 13

1

Question 14

prometaphase

Answer 14

2

Question 15

metaphase

Answer 15

3

Question 16

anaphase

Answer 16

4

Question 17

telophase

Answer 17

5

Question 18

cytokinesis

Answer 18

6

Question 19

Apoptosis

Answer 19

programmed cell death

Elimination of damaged or infected or cancer cells Correct creation of organs and limbs

Question 20

Caspases

Answer 20

Regulation of initiation of apoptosis
initiator caspases
executioner caspases

Question 21

Activation of caspase cascade:

Answer 21

extrinsic pathway (from outside)
intrinsic pathway (from inside)

Question 22

proapototic

anti-apoptotic

Answer 22

proapototic - increase cyt c release

anti-apoptotic - inhibit the release of cyt c

Question 23

what causes tumors?

Answer 23

increased cell division or decreased apoptosis