MCB Chapter 17 Homework Questions

DNA replication is initiated by____________.

S-Cdk

cohesin

nucleosome

geminin

a

M-Cdk complex is activated by_______.

inhibition of CAK phosphorylation.

phosphorylation by Wee1 kinase.

dephosphorylation by Cdc25 phosphatase.

inhibition of cyclin binding.

c

CKIs such as p27 ____________.

inhibit the cyclin-Cdk complex

activate the cyclin-Cdk complex

activate the catalytic activity of Cdk

inhibit cyclin binding to Cdk

a

Cdk activity is stimulated by phosphorylation of the T-loop by ________.

CAK

APC

Cyclin

Cdc25

a

EdU incorporation marks cells in..........

Start phase

G1 phase

S phase

M phase

c

M-cyclin _______________.

levels fall toward the end of M phase as a result of ubiquitylation and degradation.

levels rises markedly during G1 phase.

is induced by phosphorylation of cyclin.

a

Which of these techniques can be used to separate cells rapidly based on their fluorescence signal corresponding to their DNA content?

Phase contrast microscopy

Flow cytometry

Agarose gel electrophoresis

Western blotting

b

Cdk activity fluctuates during the cell cycle, partly because ________________.

cyclin levels change during the cycle

Cdks are rapidly degraded

the Cdks inactivate the cyclins

levels of Cdks fluctuate throughout the cell cycle.

a

Which of these statements about Cdc25 phosphatase is true?

Cdc25 inhibits Cdk activity.

Cdc25 maintains Wee1 phosphorylaiton of Cdk.

Cdc25 increases Cdk activity.

Cdc25 prevents Cyclin binding to Cdk.

c

One half of a duplicated chromosome at the end of S phase is called

Sister chromatid

Kinetochore

Securin

Condensin

a

A key control system crucial for triggering cytokinesis is.............

Start transition

G2/M transition

Metaphase to anaphase transition

c

If cell cycles were repeated with only the S phase and M phases, what is likely to occur?

The cells produced would get smaller and smaller.

Cells would get larger and larger.

The mitotic spindle could not assemble.

Cells would not be able to replicate their DNA.

a

Which of these fluorescently-tagged proteins can be used to monitor G2 phase in live cells?

Cdt1

APC/C

S-Cdk

Geminin

d

Which of these factors inactivates Cdks by adding phosphates on specific sites on Cdks?

Cdc25

Wee1

Greatwall kinase

Ensa

b

Activation of Greatwall kinase...........

activates PP2A-B55

inhibits PP2A-B55

inhibits M-Cdk activity

inhibits M-CDK substrate phosphorylation

b

Mutations in Ensa that prevents its binding to PP2A-B55 will...........

activate Greatwall kinase.

inhibit PP2A-B55 activity in early mitosis.

lead to constitutive phosphorylation of M-Cdk substrates.

keep PP2A-B55 active in early mitosis.

d

Which of these mechanisms serve as positive feedback to activate M-Cdks?

Addition of phosphates on M-Cdk by Wee1

Inhibition of Cdc25 activity

Inhibition of Wee1 by M-Cdk

Activation of PP2A-B25

c

CAK-dependent phosphorylation of M-Cdk is sufficient to fully activate M-Cdk activity even in the presence of Cdk phosphorylation by Wee1?

True

False

b

Cdt1 is activated by ____________.

APC/C induced destruction of geminin

accumulation of geminin

destruction of Cdc6

binding of geminin

a

During metaphase..................

nuclear envelope breaks down.

nuclear envelope re-assembles.

chromosome attach to spindle microtubules for the first time.

chromosomes align at the spindle equator.

d

Condensins ________________.

compact chromosomes when phosphorylated by M-Cdk

are made of the exact same protein subunits as cohesins

are involved in keeping the sister chromatids apart

bind to DNA in G1 phase

a

Cdc20-APC and Cdh1-APC complexes are similar because........................

They are both active throughout interphase.

They both inhibit M-Cdk activity.

They are both inactivated soon after anaphase.

They are both activated suddenly at the onset of mitosis.

b

ORC is phosphorylated in which phase?

S phase

G1 phase

G2 Phase

Mitosis

a

DNA helicase deposition on DNA at the replication origins occurs mainly in which phase of cell cycle?

G1 phase

S phase

G2 phase

mitosis

a

At the beginning of S phase in a cycling cell, which of these events are likely to occur?

Activation of Cdh1-APC/C

Activation of Cdc20

Activation of geminin

Activation of M-Cdk

c

In the metaphase to anaphase transition, activation of which of these factors is important?

Cdc20-APC/C complex

Cdh1- APC/C complex

Helicase

S-Cdk

a

Which of these complexes keep M-cyclin levels low in G1 phase of cell cycle?

Cdc20-APC/C

Skp2-SCF

p27-Cdk

Cdh1-APC/C

d

S-cdk ensures that replication happens only once per cell cycle- how?

It promotes the assembly of a prereplicative complex.

It phosphorylates the Cdc6 protein, marking it for destruction.

It phosphorylates and inactivates DNA helicases

It blocks the rise of Cdc6 concentrations early in G1.

b

If a cell in G1 phase and another cell in G0 phase are induced to pass the restriction point by the addition of a signaling molecule, but the signal is then immediately removed, what is likely to occur?

Both cells will replicate their DNA.

Only the G1 cell will replicate its DNA.

Only the G0 cell will replicate its DNA.

Neither of the cells will replicate their DNA

a

Disassembly of nuclear envelope marks which phase of mitosis?

Metaphase

Anaphase

Prometaphase

c

Which of these statements about APC is false?

APC is phosphorylated by the (mitotic) Cdk1-cyclinB and binds its activator Cdc20 to become active in metaphase.

APC is a protease and promotes anaphase by degradation of securin, the protein that holds sister chromatids together.

APC is an ubiquitin ligase and promotes anaphase by ubiquitin mediated degradation of securin.

APC is also active in ensuring exit from mitosis.

b

Which of these proteins play a direct role in anaphase B?

Kinesin-5 on interpolar microtubules and dynein on astral microtubules

Kinesin-13 on kinetochore microtubules and dynein on astral microtubules

Kinesin-5 on interpolar microtubules and kinesins 4 on interpolar and astral microtubules

Kinesin-5 on interpolar microtubules and dynein on kinetochore microtubules

a

Which of these motor proteins are minus-end directed motors that cross link interpolar microtubules and pull the poles together?

Kinesin-14

Kinesin-10

Kinesin-5

Kinesin-4

a

Duplication of centrosomes occurs in ________.

S phase

G2 phase

M phase

G1 phase

a

Polar ejection force that pulls chromosomes to the spindle equator is mediated by ______.

Kinesin-14

Kinesin-5

Dynein

Correct! Kinesin-4

d

The polar ejection force does which of the following?

Pulls the kinetochore towards the poles by plus-end depolymerization

Pushes the chromosome arms away from the spindle poles with the help of kinesin-4 and 10

Pulls the microtubules towards the spindle poles by microtubule flux

Pushes the chromosome arms towards the poles with the help of kinesin-5

b

Which of the following statements is TRUE?

The mitotic spindle helps segregate the chromosomes to the two daughter cells.

The contractile ring formation is inhibited by RhoA signaling.

The contractile ring is made largely of actin filaments.

The mitotic spindle is largely made of intermediate filaments.

a

Some cell types in animals do not have centrosomes and therefore they do not have....

Interpolar microtubules

Kinetochore microtubules

Astral microtubules

Chromatids

c

The plus ends of these microtubules are attached to large protein structures at the centromeres and they are called..............

Astral microtubules

Kinetochore microtubules

Interpolar microtubules

b

Proper bi-orientation of the sister-chromatid pair on the spindle generates a tension that is sensed by_____.

Centrioles

Aurora-B kinase

Cohesins

Kinesin-5

b

Degradation of securin is important for ________.

separation of sister chromatids

formation of spindle

activation of Cdc20-APC/C complex

inactivation of separase

a

The length of a kinetochore microtubule does not change much during metaphase because there is no addition or removal of tubulin subunits.

True

False

b

Which statement about centrosomes is TRUE?

Centrosomes are not duplicated during cell cycle.

Centrosomes are duplicated once per cell cycle similar to DNA.

Centrosomes are duplicated once per cell cycle unlike DNA.

Centrosomes are replicated multiple times during a cell cycle.

b

Contractile ring is made of ________.

actin and myosin filaments

kinetochore microtubules

nuclear lamins

astral microtubules

a

Disassembly of the nuclear envelope ________________.

causes the inner nuclear membrane to separate from the outer nuclear membrane.

must occur for kinetochore microtubules to form in animal cells.

results in the conversion of the nuclear envelope into protein-free membrane vesicles.

is triggered by the phosphorylation of integrins.

b

Which statement about kinetochores is true?

Kinetochores assemble on chromosomes that lack centromeres.

Kinetochores assemble onto chromosomes during late prophase.

Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome.

Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules.

b

Which event indicated below happens before the nuclear envelope is re-assembled in M phase?

decondensation of chromosomes

completion of telophase.

assembly of the contractile ring

reassembly of the nuclear lamina

c

Which statement about drugs targeting microtubules is FALSE?

Drugs such as colchicine that inhibit microtubule polymerization, inhibit mitosis.

Drugs that stabilize microtubules such as Taxol promote mitosis by stabilizing the spindle.

Drugs that stabilize microtubules such as Taxol inhibit mitosis.

b

What are mitogens?

They are extracellular signals that stimulate cell division.

They are transcription factors that induce cell death.

They are kinases that inhibit cell proliferation.

They are produced by mitotic cells to keep nearby neighboring cells from dividing.

a

DNA damage induced checkpoint response in G1 ________________.

involves the inhibition of cyclin-Cdk complexes by p21.

causes cells to proceed through S phase more quickly.

involves the degradation of p53.

is activated by inhibition of ATM.

a

UV exposure can cause DNA damage. Which of the following would you NOT expect to occur as a result of genomic damage?

Activation of the protein kinase ATR

Activation of the protein kinase Chk1

Inactivation of the protein phosphatase Cdc25

Binding of p53 to Mdm2

d

Which event contributes to helping the cells progress from G1 to S phase?

Activation of E2F gene expression

Destruction of CKIs that target S-Cdks

Phosphorylation of Rb by G1-Cdk, G1/S-Cdk, and S-Cdk

All of the above

d

Which of these is an immediate early gene whose expression is triggered by Ras activation to promote cell cycle entry?

mTOR

Myc

S-Cyclin

Ubiquitin ligase

b

ATM and ATR kinases phosphorylate Ser-15 residue in p53 which________.

Inhibits p53

Enhances its interaction with Mdm2

Stabilizes p53

Inhibits p21

c

G1/S Cdk also phosphorylates and inactivates APC/C towards end of G1 phase, which directly helps in accumulation of ..................

Rb

S-Cyclin

p53

ATR

b

Retinoblastoma is caused by excessive proliferation of some cells in retina that is induced by ..................

high Rb activity

high CKI activity

high E2F activity

high p53 activity

c

The Chk1-mediated checkpoint response to DNA damage can arrest cells in G2/M phase by inhibiting which of these factors?

ATM

ATR

Cdc25

Rb

c

Which of these is the purpose of activating cell cycle checkpoint responses to DNA damage?

promote cell death if damage is excessive.

halt cell cycle to facilitate DNA repair.

halt cell cycle to suppress accumulation of mutations.

All of the above.

d

p53 expression is often lost in early stages of cancer development, and in the absence of p53, which of these factors serve to initiate key cell cycle checkpoint-response to DNA damage? (see lecture-8 ppt.)

p21

14-3-3 sigma

Chk1

Wnt

c

A regulator critical for enhancing cell growth through stimulation of protein synthesis rates is ...........

mTORC1

TSC

Gator1

Chk1

a