Chp. 18 - Cell Cycle

Question 1

What would be the most obvious outcome of repeated cells consisting of S phase and M phase only?

Answer 1

The cells produced would get smaller and smaller.

Question 2

Levels of Cdk activity during the cell cycle, in part because ____.

Answer 2

cyclin levels change during the cycle

Question 3

____ drives cells through G1.

Answer 3

G1-Cdk

Question 4

_____ and ____ drives it into S phase.

Answer 4

G1/S-Cdk; S-Cdk

Question 5

G1/S-Cdk and S-Cdk drives it into ___ phase.

Answer 5

S

Question 6

___ initiates DNA replication during S phase and helps ensure the genome is copies only once.

Answer 6

S-Cdk

Question 7

Centrosomes duplicate during __ phase and separate during ___.

Answer 7

S; G2

Question 8

____ drives the cell into mitosis.

Answer 8

M-Cdk

Question 9

Cyclins concentrations are regulated by ____ and ____.

Answer 9

transcription and proteolysis

Question 10

Cyclins are regulated…. ______ via gradual increase in cyclins. ____ via quick decrease in cyclins.

Answer 10

transcription; proteolysis

Question 11

What is APC?

Answer 11

Anaphase Promoting Complex

Question 12

Cyclin concentration is regulated by ___ and ____.

Answer 12

transcription; proteolysis

Question 13

The activity of cyclin-cdk complexes depends on ___ and ___.

Answer 13

phosphorylation; dephosphorylation

Question 14

When the M cyclin and the mitotic Cdk make a complex, they have two phosphates that were put there by ____.

Answer 14

inhibitory kinase (Wee1)

Question 15

The cyclin Cdk complex contains inhibitory phosphates This modification keeps M-Cdk in a/an _____.

Answer 15

inactive state

Question 16

For the M-Cdk to become active, it must dephosphorylated by ____.

Answer 16

CDC 25

Question 17

CDC 25 actually involved in activation of ____.

Answer 17

M-Cdk

Question 18

Cdk activity can be blocked by ______ proteins.

Answer 18

Cdk Inhibitor

Question 19

What inhibitor makes the active cyclin-Cdk complex inactive?

Answer 19

p27

Question 20

What is the main molecular difference between cells in a G0 state and cells that have simply paused in G1?

Answer 20

* Cells in the G0 state do not divide * In G0, the cell-cycle control system is partly dismantled, so that some of the Cdks and cyclins are not present. Cell paused in G1, by contrast, still contain all the components of the cell-cycle control system. Whereas the latter cells can rapidly progress through the cycle when conditions are right, G0, cells need to synthesize the missing cell-cycle control proteins so as to re-enter the cycle, which usually takes 8 hours or more.

Question 21

___ are extracellular signal that stimulate cell division by the production of the cyclins. If deprived of this signal, the cell cycle arrests in __.

Answer 21

Mitogens; G1

Question 22

The ___ protein blocks cells from entering the cell cycle by inhibiting cyclin transcription.

Answer 22

Rb

Question 23

Mitogens promote cell division by activating ___ and ___ which inactivate the __ proteins.

Answer 23

G1-Cdk; G1/Cdks; Rb

Question 24

DNA damage can arrest the cell cycle in __.

Answer 24

G1

Question 25

How does S-Cdk help guarantee that replication occurs only once during each cell cycle?

Answer 25

It phosphorylates the Cdc6 protein making it for destruction.

Question 26

Sister chromatids are held together by ___ complexes until anaphase.

Answer 26

cohesin ring

Question 27

Activation of __ by ___ leads to entry into M phase.

Answer 27

M-Cdk; Cdc25

Question 28

Before a cell can enter M phase, what two structures must be duplicated?

Answer 28

1- DNA must be fully replicated; 2- The centrosome must be duplicated

Question 29

Centrosome duplication begins at the start of the __ phase and is complete by the end of \_\_\_.

Answer 29

S; G2

Question 30

Which of the following correctly matches the phase of the eukaryotic cell cycle with an event that takes place in that phase?

Answer 30

M phase—cytokinesis

Question 31

Which is NOT a transition point where the cell cycle control system regulates progression through the cell cycle?

Answer 31

S/G2 transition

Question 32

The expression levels of different ___________ fluctuate throughout the cell cycle.

Answer 32

cyclins

Question 33

The slow rise of S cyclin levels throughout G1 phase is due to \_\_\_\_\_\_\_\_\_\_\_, and the abrupt decrease is caused by \_\_\_\_\_\_\_\_\_\_\_.

Answer 33

transcription; proteolysis

Question 34

In response to DNA damage, the ___________ protein is phosphorylated and activates the transcription of a Cdk inhibitor to halt cell cycle progression.

Answer 34

p53

Question 35

How does S-Cdk prevent re-replication?

Answer 35

phosphorylation of ORC and Cdc6

Question 36

M-Cdk is suddenly activated at the end of G2 by \_\_\_.

Answer 36

dephosphorylation by Cdc25

Question 37

What is the function of cohesins?

Answer 37

hold two sister chromatids together during replication.

Question 38

The figure below shows some steps involved in the initiation of DNA replication. What is the identity of the complex labeled "B"?

Answer 38

ORC

Question 39

What accounts for the difference in the curve shapes depicting the concentration of M-cyclin versus M-Cdk activity during the cell cycle?

Answer 39

The M-Cdk complex is not activated until M-cyclin is bound and M-Cdk is dephosphorylated.

Question 40

Consider an animal cell that has 8 chromosomes (four pairs of homologous chromosomes) in the G1 phase. How many of each of the following structures will the cell have at mitotic prophase? A. sister chromatids B. centromeres C. kinetochores D. centrosomes E. Centrioles

Answer 40

A. sister chromatids: 16 B. centromeres: 16 C. kinetochores: 16 D. centrosomes: 2 E. Centrioles: 4

Question 41

If chromosome is attached to two microtubules from opposite poles and one of the microtubules is experimentally severed, what occurs?

Answer 41

The chromosomes migrate quickly to the pole to which it is still attached.

Question 42

In the cells of some organisms, mitosis occurs without cytokinesis. This will result in...

Answer 42

cells with more than one nucleus

Question 43

Place the numbers 1-8 next to the letter headings to indicate the normal order of events. A. alignment of the chromosomes at the spindle equator; B. attachment of spindle microtubules to chromosomes; C. breakdown of the nuclear envelope; D. pinching of cell in two; E. separation of two centrosomes and initiation of mitotic spindle assembly; F. re-formation of the nuclear envelope; G. condensation of the chromosomes; H. separation of sister chromatids

Answer 43

A. 5, metaphase B. 4, prometaphase C. 3, prometaphase D. 8, cytokinesis E. 2, prophase F. 7, telophase G. 1, prophase H. 6, anaphase

Question 44

The number of cells in adult tissue or animal depends on cell proliferation. What else does it depend on?

Answer 44

Programmed cell death also influences cell numbers. Most animal cells require survival signals from other cells to avoid programmed cell death so that the levels of such signals can help determine how many cells live and how many die.

Question 45

Bax and Bak promote apoptosis by releasing ____ from the mitochondria.

Answer 45

cytochrome c

Question 46

What is the cause of the massive amount of programmed cell death of nerve cells (neurons) that occurs in the developing vertebrate nervous system, and what purpose does it serve?

Answer 46

Immature neurons are produced in excess of the number that will eventually be required. They compete for the limited amount of survival factors secreted by the target cells they contact. THOSE CELLS THAT FAIL TO GET ENOUGH SURVIVAL FACTOR UNDERGO PROGRAMMED CELL DEATH. Up to half or more of the original nerve cells die in this way. This competing mechanism helps match the number of developing nerve cells to the number of target cells they contact.

Question 47

Cohesin is cleaved by the enzyme \_\_\_\_\_\_\_\_\_\_\_, which is held in an inactive state by ___________ until it is degraded by the APC/C complex.

Answer 47

separase; securin

Question 48

What drives the reassembly of the nuclear envelope?

Answer 48

dephosphorylation of lamins

Question 49

The contractile ring is composed of

Answer 49

actin and myosin.

Question 50

In response to an apoptotic stimulus, initiator caspases

Answer 50

cleave and activate executioner caspases.

Question 51

Which of the following cells died by apoptosis?

Answer 51

B

Question 52

Consider an animal cell that has eight chromosomes (four pairs of homologous chromosomes) in G1 phase. This cell has \_\_\_\_\_\_\_\_\_sister chromatids and \_\_\_\_\_\_\_\_\_ centrioles.

Answer 52

16; 4

Question 53

If a chromosome is attached to two microtubules from opposite poles and one of the microtubules is experimentally severed, what occurs?

Answer 53

The chromosome migrates quickly to the pole to which it is still attached.

Question 54

What is the function of condensins?

Answer 54

to coil sister chromatids into a compact form

Question 55

In which phase of mitosis does the nuclear envelope break down?

Answer 55

prometaphase

Question 56

How are spindle microtubules attached to chromosomes?

Answer 56

The minus ends of the microtubules bind directly to a protein complex on DNA. The plus ends of the microtubules bind directly to DNA. The microtubules bind to cohesion complexes on the DNA. The microtubules bind to the kinetochore complexes through a connecting protein.\*\*\*

Question 57

The four phases of the cell cycle, in order, are G1, \_\_, \_\_\_\_\_\_2, and \_\_\_\_\_\_. A cell contains the most DNA after _________ phase of the cell cycle. A cell is smallest in size after _____ phase of the cell cycle. Growth occurs in \_\_\_\_\_\_\_\_, \_\_\_\_\_\_\_, and \_\_\_\_\_\_phases of the cell cycle. A cell does not enter mitosis until it has completed _________ synthesis.

Answer 57

G1 --\> S --\> G2 --\> M; S phase; M phase; G1, S, and G2; DNA

Question 58

Different Cyclin-Cdk complexes Trigger Different Steps in the Cell Cycle. The cyclin that acts in G2 to trigger entry into M phase is called \_\_\_\_\_\_\_\_\_\_\_, and the active complex it forms with its Cdk is called \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, Other cyclins, called _______ and \_\_\_\_\_\_\_\_\_\_\_\_\_, bind to a distinct Cdk protein late in G1 to form S-Cdk and G1/S-Cdk; these cyclin –Cdk complexes help launch S phase. Another group of cyclins, called \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, act earlier in G1 and bind to other Cdk proteins to form \_\_\_\_\_\_\_\_\_, which help drive the cell through G1.

Answer 58

Different Cyclin-Cdk complexes Trigger Different Steps in the Cell Cycle. The cyclin that acts in G2 to trigger entry into M phase is called _M cyclin_ and the active complex it forms with its Cdk is called _M-Cdk_, Other cyclins, called _S cyclins_ and _G1/S_, bind to a distinct Cdk protein late in G1 to form S-Cdk and G1/S-Cdk; these cyclins –Cdk complexes help launch S phase. Another group of cyclins, called _G1 cyclin_, act earlier in G1 and bind to other Cdk proteins to form _G cdk_, which helps drive the cell through G1.

Question 59

The interval between the completion of mitosis and the beginning of DNA synthesis is called \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, and the interval between the end of DNA synthesis and the beginning mitosis is called \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.

Answer 59

G1; G2

Question 60

The cell-cycle control system depends on \_\_\_\_\_\_\_\_\_\_\_\_-dependent protein kinases (Cdks), which are cyclically activated by the binding of \_\_\_-\_\_\_\_\_\_\_\_\_\_ proteins and by phosphorylation and \_\_\_\_\_\_\_\_\_\_\_\_\_; when activated, Cdks phosphorylate key proteins in the cell.

Answer 60

cyclin; cyclin; dephosphorylation