chapter 18

Question 1

Cells reproduce by _ a process called the _.

Answer 1

duplicating their contents and dividing in two in
_
cell cycle

Question 2

The cell grows continuously during _, which consists of _

Answer 2

interphase
_
three phases: G1, S, and G2.

Question 3

DNA replication is confined to _

Answer 3

S phase.

Question 4

During M phase, the _ divides in a process called mitosis; then
the _ divides, in a process
called cytokinesis.

Answer 4

nucleus
cytoplasm

Question 5

During M phase, the nucleus divides in a process called _; then
the cytoplasm divides, in a process
called _.

Answer 5

mitosis
cytokinesis

Question 6

M phase, for example, is typically much _and G1 much _ .

Answer 6

shorter
longer

Question 7

The cell-cycle control system ensures that key processes in the cycle _

Answer 7

occur in the proper sequence.

Question 8

The control system can transiently halt the cycle at specific transition points—in _— if _.

Answer 8

G1, G2, and M phase
_
extracellular or intracellular conditions are unfavorable

Question 9

checks before entering in MITOSIS

Answer 9

Is all DNA replicated? Is all DNA damage repaired?

Question 10

checks before PULL DUPLICATED CHROMOSOMES APART

Answer 10

Are all chromosomes properly attached to the mitotic spindle?

Question 11

checks before ENTER S PHASE

Answer 11

Is environment favorable?

Question 12

Distinct Cdks associate with different _ to trigger the different events of the cell cycle.

Answer 12

cyclins

Question 13

Distinct _ associate with different cyclins to trigger the different events of the cell cycle.

Answer 13

Cdks

Question 14

cyclins that are specifically active during the G1 phase of the cell cycle:

Answer 14

cyclin D

Question 15

cyclins that help G1 –> S transition:

Answer 15

cyclin E

Question 16

cyclins that are specifically active during the S phase of the cell cycle:

Answer 16

cyclin A

Question 17

cyclins that are specifically active during the M phase of the cell cycle:

Answer 17

cyclin B

Question 18

The activity of some Cdks is regulated by _

Answer 18

cyclin degradation.

Question 19

_ of S or M cyclin by _ marks the protein for destruction in proteasomes. The loss of cyclin renders _

Answer 19

Ubiquitylation
_
APC/C
_
its Cdk partner inactive.

Question 20

For M-Cdk to be active, _.

Answer 20

inhibitory phosphates must be removed

Question 21

As soon as the M cyclin–Cdk complex is formed, it is _ by an _ called _. This modification keeps M-Cdk in an _ state until these phosphates are removed by an _ called _.
!!!!mechanism specific to M-Cdks!!!!!

Answer 21

phosphorylated at two adjacent sites
_
inhibitory protein kinase
_
Wee1
_
inactive
_
activating protein phosphatase
_
Cdc25

Question 22

The activity of a Cdk can be blocked by the _

Answer 22

binding of a Cdk inhibitor. eg: inhibitor protein (called p27) binds to an activated cyclin–Cdk complex = prevents the Cdk from phosphorylating target proteins

Question 23

control mechanism when
DNA replication not complete
DNA damage

Answer 23

INHIBITION OF ACTIVATING PHOSPHATASE (Cdc25) BLOCKS ENTRY TO MITOSIS

Question 24

control mechanism when chromosomes not properly attached to spindle

Answer 24

INHIBITION OF APC/C ACTIVATION DELAYS EXIT FROM MITOSIS

Question 25

control mechanism when environment not favorable

Answer 25

Cdk INHIBITORS BLOCK ENTRY TO S PHASE

Question 26

mitogens :

Answer 26

stimulate cell proliferation

Question 27

mitogens inhibit

Answer 27

the Rb protein.

Question 28

dephosphorylated Rb protein (active), what do they do?

Answer 28

holds specific transcription regulators in an inactive state.

Question 29

Mitogens binding to _ activate _ that lead to the _. These complexes _, and thereby inactivate, the _ protein, releasing the transcription regulators needed to activate the transcription of genes required for entry into S phase.

Answer 29

cell-surface receptors _ intracellular signaling pathways _ formation and activation of G1-Cdk and G1/S-Cdk complexes _ phosphorylate _ Rb

Question 30

DNA damage can arrest the cell cycle in _.

Answer 30

G1

Question 31

When DNA is damaged, specific protein kinases respond by both activating the _ and halting _. _ protein thus accumulates and stimulates the _. The p21 protein binds to G1/S-Cdk and S-Cdk and inactivates them, so that the cell cycle arrests in G1.

Answer 31

p53 protein _ its otherwise rapid degradation _ Activated p53 _ transcription of the gene that encodes the Cdk inhibitor protein p21 (same shape and system as p27) _

Question 32

explain the initiation of DNA replication (fig 16)

Answer 32

During G1, Cdc6 on ORC (origin recognition complex sitting on origin) _ HELICASE BINDS, Cdc6 DISSOCIATES from ORC _ At the start of S, S-Cdk triggers the firing of this loaded replication origin _ S-Cdk also blocks re-replication by phosphorylating Cdc6 and the ORC = both inactive = prevents reassembly of the prereplicative complex until the Cdks are turned off in the next G1.

Question 33

Activated M-Cdk indirectly activates _, creating a _

Answer 33

more M-Cdk positive feedback loop.

Question 34

APC/C triggers _ by _

Answer 34

the separation of sister chromatids _ by promoting the destruction of cohesins.

Question 35

APC/C catalyzes the _ and _ of an _ protein called _, which _ the activation of a proteolytic enzyme called _. When freed from _, _ cleaves the _, allowing the _.

Answer 35

ubiquitylation _ destruction _ inhibitory _ securin _ blocks _ separase _ securin _ separase _ cohesin complexes _ mitotic spindle to pull the sister chromatids apart

Question 36

(A) In anaphase A, _ The force driving this movement is generated mainly at the _.

Answer 36

the sister chromatids are pulled toward opposite poles as the kinetochore microtubules depolymerize. _ kinetochore

Question 37

(B) In anaphase B, _ as the result of two separate forces: (1) _, and (2) _ Both forces are thought to depend on _

Answer 37

the two spindle poles move apart _ the elongation and sliding of the interpolar microtubules past one another pushes the two poles apart _ Microtubules at the edges (astral microtubules) are pulled toward the cell edges dragging the two poles apart. _ the action of motor proteins associated with the microtubules.

Question 38

The nuclear envelope breaks down and re-forms during mitosis. The _ of _ and _ helps trigger the disassembly of the nuclear envelope at _. _ of these proteins at telophase helps reverse the process.

Answer 38

phosphorylation _ nuclear pore proteins _ lamins _ prometaphase _ Dephosphorylation