EXAM II White

Question 1

What are the major chromosomal events in the cell cycle? (3)

Answer 1

S phase - duplication
M phase - segregation
Cytokinesis

Question 2

What are the 4 phases of the cell cycle?

Answer 2

G1 phase
S phase - DNA synthesis
G2 phase
M phase - chrom. separation and division

Question 3

What are the 3 checkpoints in the cell cycle?

Answer 3

G1 to S

G2 to M

Anaphase to Cytokinesis in the M phase

Question 4

List the 3 classes of cyclins, what are their functions?

Answer 4

1. G1/S cyclin - triggers progression thru START, commitment into cell cycle
2. S-cyclin - stimulates chrom duplication, high until mitosis
3. M-cyclin - entry into mitosis at G2/M checkpoint, M-cyclins removed at Mid-mitosis

Question 5

Describe the mechanism in which T-loop and CAK control cyclin-Cdk activity; when is Cdk inactive? when is it active? What is the function of CAK?

Answer 5

Inactive = cyclin not bound to Cdk and is blocked by T loop

T-loop moves from active site when cyclin binds (making Cdk partially active)

Cdk is phosphorylated via CAK (Cdk activating kinase)

Question 6

Phosphorylation and dephosphorylation is a way to regulate Cdk, explain this mechanism

(M-Cdk activation)

Answer 6

Wee1 kinase puts an inhibitory phosphate on the roof site and Cdc25 dephosphylates the roof site rendering it active

Question 7

Cdk inhibitory proteins (CKI) is a way to regulate Cdk activity, explain this mechanism, which part of the cell cycle is this primarily used for? What disease is this associated with?

Answer 7

CKI (p27) binds both Cdk and cyclin = inactive usually used to control G1/S-Cdks and S-Cdks early in cell cycle

Disease = CKI = INK4A involved in G1 phase causing CKI to lose its function

Question 8

What is the function of p53 and p21, explain their relationship

Answer 8

p53 = tumor suppressor, upregulates p21

p21 = a CKI; p53 generates p21 transcription, if low p21 expression = cells divide uncontrollably

Question 9

Proteolysis of CKIs can turn on ______ via ______

Answer 9

S-Cdks via SCF via ubiquitin ligase which adds ubiquitin

Can occur in G1, which activates S-Cdks (restoring DNA replication)

SCF activity depends on F-Box proteins

Question 10

What is the key regulator for the progression from metaphase to anaphase?

Answer 10

APC/C - anaphase promoting complex (a ubiquitin ligase)

Question 11

What are the 4 ways in which cyclin-Cdk activities is regulated? (name 2 for exam)

Answer 11

Cdk phosphorylation
Binding of CKI
Proteolysis of Cyclins
Ubiquination of proteins

Question 12

List the two important functions of APC/C

Answer 12

1. Regulates the transition from metaphase to anaphase
2. Triggers cyclin destruction via ubiquitin, Cdk inactivation by destroying Cdk-cyclin complexes (S- and M-cyclins) and dephosphorylation of Cdk targets

Question 13

Define pre-replicative complex (pre-rc), what inhibits their assembly? At which phase is it disassembled?

Answer 13

Assembles at OriR during G1 phase; disassembled at S phase

Ensures that DNA is only replicated ONCE

Inhibited by Cdk (S-cdk) activity; APC/C causes dephosphorylation of Pre-RC

Question 14

Components of the pre-rc cannot form a new PRE-RC complex until M-Cdk is inactivated and APC/C is activated at end of mitosis

Answer 14

.

Question 15

What other protein is condensin related to?

Answer 15

Cohesin = which holds sister chromatids together

Question 16

Which Cdk-cyclin complex triggers the assembly of the mitotic spindle?

Answer 16

M-Cdk

Question 17

Structure of microtubules?

Answer 17

Heterodimer with alpha- and beta-tubulin linked by non-covalent bonds

Question 18

List the 3 types of microtubules

Answer 18

KIA

Kinetochore
Interpolar
Astral

Question 19

Function of the interpolar microtubules?

Answer 19

Hold the two halves of the spindle together; plus ends from each side interact with each other

Question 20

Function of kinetochore microtubules?

Answer 20

Attaches each chromosome to the spindle pole

Question 21

Microtubules are made up of alpha and beta-tubulins, what is the function of gamma-tubulin?

Answer 21

Nucleation of microtubule growth from the MTOC via gamma-tubulin ring complex

Nucleation occurs at the (-) end

Question 22

Function of Ndc80 complex in the kinetochore?

Answer 22

Anchoring protein that attaches the kinetochore to the microtubule

Kinetochores contain an open end allowing addition and removal of subunits

Question 23

List the 4 different types of motor proteins involved in spindle assembly and state their functions

Answer 23

Kinesin-5 - moves towards (+) ends, forcing centrosomes of the mitotic spindle apart (of the interpolar microtubules)

Kinesin-4,10 - moves towards (+) ends, pushing attached chromosomes away from the pole, while kinetochore is pulling toward (-) end (polar ejection force)

Kinesin-14 - moves towards (-) ends, pulling poles together (push-pull w/ kinesin 5)

Dynein - (-) end; links astral microtubules to actin skeleton at cell cortex; pulls spindle poles away from each other

Question 24

Mitotic spindle will collapse if which motor protein was not present?

Answer 24

Kinesin-5

Question 25

List the 3 forces of chromosomal movement

Answer 25

Dick Meets Penis

1. Depolymerization
2. Microtubule flux
3. Polar ejection force

Question 26

Depolymerization is a type of chrom movement, explain what it does

Answer 26

Pulls kinetochore and chromosome towards the spindle pole driven by depolymerization

Question 27

Microtubule flux is a type of chrom movement, explain what it does

Answer 27

The escalator

Microtubules are moved toward spindle pole while being dismantled at (-) ends and tubulin is being added at (+) end

Question 28

Polar ejection force is a type of chrom movement, explain what it does. Which motor protein is involved?

Answer 28

Kinesin-4,10 motors on chromosomes interact with microtubules and transport chrom. from poles

Push-pull phenomenon

Question 29

What is the function of mitogens

Answer 29

Stimulate cell division by triggering G1/s-Cdk activity