Cell cycle ( the cell cycle control system)

Question 1

operates like a timer that triggers the events of the cell cycle in a set sequence

Answer 1

cell-cycle control system

Question 2

delay progression to M phase

Answer 2

malfunction

Question 3

provide time for the machinery to be repaired and also prevent the disaster that
might result if the cycle progressed prematurely to the next stage

Answer 3

delay progression to M

Question 4

based on a connected series of biochemical switches

Answer 4

cell-cycle control system

Question 5

Where is cell-cycle control system based on?

Answer 5

connected series of biochemical switches

Question 6

Each of connected series of biochemical switches possesses many important features that increase the?

Answer 6

accuracy and reliability of cell-cycle progression

Question 7

the switches are in a irreversible fashion

Answer 7

binary (on/off)

Question 8

irreversible fashion of switches would clearly be disastrous if?

Answer 8

if events like chromosome condensation or nuclear-envelope breakdown were only partially initiated or started but not completed.

Question 9

the cell-cycle control system is remarkably _____ and _____ because backup
mechanisms allow the system to operate effectively under a variety of conditions

Answer 9

robust and reliable

Question 10

remarkably robust and reliable, partly because of backup mechanisms

Answer 10

cell-cycle control system

Question 11

highly adaptable and can be modified to suit specific cell types or to respond to
specific intracellular or extracellular signals.

Answer 11

cell-cycle control system

Question 12

three major regulatory transitions

Answer 12

1. Start (restriction point) in late G1
2. G2/M transition
3. metaphase-to-anaphase

Question 13

cell commits to cell-cycle entry and
chromosome duplication

Answer 13

Start (restriction point) in late G1

Question 14

Where do cell commits in Start (restriction point) in late G1

Answer 14

cell-cycle entry and chromosome duplication

Question 15

Control system triggers the early mitotic events that lead to chromosome alignment on the mitotic spindle in metaphase

Answer 15

G2/M transition

Question 16

control system stimulates sister-chromatid separation leading to the completion of mitosis and cytokinesis

Answer 16

metaphase-to-anaphase transition

Question 17

G2/M transition triggers the early mitotic
events that lead to?

Answer 17

chromosome alignment on the mitotic spindle in metaphase

Question 18

metaphase-to-anaphase stimulates
sister-chromatid separation, leading to

Answer 18

completion of mitosis and cytokinesis

Question 19

What does the control system do if extracellular conditions are not appropriate for cell proliferation?

Answer 19

blocks progression through each of these
transitions if it detects problems inside or
outside the cell

Question 20

Central components of the cell-cycle control system are members of a family of
protein kinases known as?

Answer 20

cyclin-dependent kinases (Cdks)

Question 21

The activities of cyclin-dependent kinases (Cdks) ____ and ___as the cell progresses through the cycle

Answer 21

rise and fall

Question 22

The rise and fall activities of Cdks lead to what

Answer 22

cyclical changes in the phosphorylation of intracellular proteins that initiate or regulate the major events of the cell cycle

Question 23

Cdks are controlled by?

Answer 23

cyclins

Question 24

four classes of cyclins

Answer 24

1. G1/S-cyclins
2. S-cyclins
3. M-cyclins
4. G1-cyclins

Question 25

activate Cdks in late G1

Answer 25

G1/S-cyclin

Question 26

what does G1/S-cyclin activaye

Answer 26

Cdks in late G1

Question 27

bind Cdks soon after progression through Start and help stimulate chromosome duplication

Answer 27

S-cyclins

Question 28

S-cyclins bind Cdks soon after progression through?

Answer 28

Start

Question 29

activate Cdks that stimulate entry to mitosis at the G2/M transition

Answer 29

M-cyclins

Question 30

M-cyclins activate Cdks that stimulate entry to?

Answer 30

mitosis at the G2/M transition

Question 31

govern the activities of the G1/S-cyclins

Answer 31

G1-cyclins

Question 32

single Cdk protein binds all classes of cyclins

Answer 32

In yeast cells

Question 33

In yeast cells, a ___ Cdk protein binds all classes of ___

Answer 33

single cyclins

Question 34

Have four Cdks

Answer 34

vertebrate cells

Question 35

How many Cdks interact with G1-cyclins in vertebrate cells?

Answer 35

Two

Question 36

Out of 4 Cdks in vertebrate cells, only 2 interacts with?

Answer 36

G1-cyclins

Question 37

How many Cdks interact with G1/S- and S-cyclins in vertebrate cells?

Answer 37

1

Question 38

Out of 4 Cdks in vertebrate cells, only 1 interacts with?

Answer 38

1. G1/S- and S-cyclins 2. S- and M-cyclins

Question 39

How many Cdks interact with S- and M-cyclins in vertebrate cells?

Answer 39

1

Question 40

4 different cyclin–Cdk complexes

Answer 40

1. G1-Cdk 2. G1/S-Cdk 3. S-Cdk, and 4. M-Cdk

Question 41

How do different cyclin–Cdk complexes trigger different cell-cycle events?

Answer 41

Cyclin protein does not simply activate its Cdk partner but also directs it to specific target proteins. As a result, each cyclin–Cdk complex phosphorylates a different set of substrate proteins.

Question 42

phosphorylates a different set of substrate proteins

Answer 42

cyclin–Cdk complex

Question 43

in the absence of _____, active site in the Cdk protein is partly obscured by a protein loop

Answer 43

Cyclin

Question 44

in the absence of cyclin, the active site in the ____protein is partly obscured by a _____ ____

Answer 44

Cdk protein loop

Question 45

causes the loop to move away from the active site, resulting in partial activation of the Cdk enzyme

Answer 45

Cyclin binding

Question 46

Cyclin binding causes the ___ to move away from the ____ ___, resulting in partial activation of the ___enzyme

Answer 46

loop active site Cdk enzyme

Question 47

occurs when a separate kinase, the Cdk-activating kinase (CAK), phosphorylates an amino acid near the entrance of the Cdk active site.

Answer 47

full activation of the cyclin–Cdk

Question 48

Full activation of the cyclin–Cdk complex then occurs when ?

Answer 48

Cdk-activating kinase (CAK) phosphorylates an amino acid near the entrance of the Cdk active site

Question 49

inhibits the activity of a cyclin–Cdk complex

Answer 49

Phosphorylation at a pair of amino acids in the roof of the kinase active site

Question 50

Phosphorylation of active site by ____ inhibits Cdk activity

Answer 50

Wee1

Question 51

_______ of active site by Wee1 inhibits Cdk activity

Answer 51

Phosphorylation

Question 52

dephosphorylation of these sites by _____ increases Cdk activity

Answer 52

Cdc25 phosphatase

Question 53

_____ of these sites by Cdc25 phosphatase increases Cdk activity

Answer 53

dephosphorylation

Question 54

Binding of ___ ____ ____ inactivates cyclin–Cdk complexes.

Answer 54

Cdk inhibitor proteins (CKIs)

Question 55

Binding of Cdk inhibitor proteins (CKIs) inactivates?

Answer 55

cyclin–Cdk complexes

Question 56

progression through the metaphase- to-anaphase transition is triggered by ____ ____, leading to the final stages of cell division

Answer 56

protein destruction

Question 57

a member of the **ubiquitin** **ligase** family of enzymes

Answer 57

anaphase-promoting complex or cyclosome (APC/C)

Question 58

used in numerous cell processes to stimulate the proteolytic destruction of specific regulatory proteins

Answer 58

anaphase-promoting complex, or cyclosome (APC/C)

Question 59

APC/C are used in numerous cell processes to stimulate the ______ ____of specific regulatory proteins. They _________ specific target proteins, resulting in their destruction in ______.

Answer 59

proteolytic destruction polyubiquitylate proteasomes

Question 60

The APC/C catalyzes the ubiquitylation and destruction two major types of proteins :

Answer 60

securin S- and M-cyclins

Question 61

protects the protein linkages that hold sister-chromatid pairs together in early mitosis

Answer 61

securin

Question 62

What does securin protect?

Answer 62

protein linkages that hold sister-chromatid pairs together

Question 63

destruction of securin

Answer 63

destroyed at metaphase

Question 64

destruction inactivates most Cdks in the cell

Answer 64

S- and M-cyclins

Question 65

many proteins phosphorylated by Cdks from S phase to early mitosis are ______

Answer 65

dephosphorylated

Question 66

- ubiquitin ligase - ubiquitylate CKI proteins in late G1 - destruction of G1/Scyclins in early S phase

Answer 66

SCF

Question 67

SCF is also responsible for the destruction of?

Answer 67

G1/S-cyclins in early S phase

Question 68

changes in its association with an activating subunit—either Cdc20 in mid-mitosis or Cdh1 from late mitosis through early G1.

Answer 68

APC/C activity

Question 69

APC/C activity changes during the cell cycle, primarily as a result of changes in its association with an activating subunit—either?

Answer 69

Cdc20 in mid-mitosis or Cdh1 from late mitosis through early G1

Question 70

- depends on substrate-binding subunits called F-box proteins. - constant during the cell cycle

Answer 70

SCF activity

Question 71

SCF activity depends on substrate-binding subunits called?

Answer 71

F-box proteins

Question 72

cell-cycle depends exclusively on post-transcriptional mechanisms that involve the regulation of Cdks and ubiquitin ligases and their target proteins

Answer 72

in early animal embryos

Question 73

in early animal embryos cell-cycle control depends exclusively on?

Answer 73

post-transcriptional mechanisms

Question 74

In the more complex cell cycles of most cell types, ______ ____provides an important additional level of regulation

Answer 74

transcriptional control