Cell Cycle

Question 1

What happens in prophase?

Answer 1

Cell begins to assemble mitotic spindle, microtubules extend from centromeres

Question 2

What occurs during prometaphase?

Answer 2

Nuclear envelope disintegrates and microtubules of mitotic spindle attach to chromosomes

Question 3

What occurs during metaphase?

Answer 3

Chromosomes are lined up the mitotic spindle and there is a pause to allow all chromosomes to become attached

Question 4

What occurs in anaphase?

Answer 4

Cohesin proteins that bind sister chromatids together are cleaved and chromosomes are pulled apart by the mitotic spindle

Question 5

What occurs in telophase?

Answer 5

Nuclear membrane reconstitutes around each set of chromosomes

Question 6

Describe G0 phase of the cell cycle

Answer 6

Quiescent (inactive), intact proliferation capacity and non-cycling
Most cells of the body are in this phase

Question 7

Describe G1 phase

Answer 7

Period between completion of cell division and DNA replication where cells start building cell mass

Question 8

Describe S phase of the cell cycle

Answer 8

DNA replication

Question 9

Describe G2 phase of the cell cycle

Answer 9

Period between completion of DNA replication and initiation of cell division

Question 10

What occurs during the M phase of the cell cycle?

Answer 10

Mitosis

Question 11

How can you measure which phase cells are in during the cell cycle?

Answer 11

Can be measured using fluorescent dye that binds to DNA

Then the cells are passed through a flow cytometer which measures the fluorescence intensity

Question 12

In which phase of the cell cycle is DNA 2n?

Answer 12

G1 phase

Question 13

During which phase is the DNA 4n?

Answer 13

G2/M phase

Question 14

During which phase is the DNA between 1n and 2n?

Answer 14

S phase

Question 15

What complexes are positive regulators of the cell cycle?

Answer 15

Cdk-Cyclins

Question 16

What are negative regulators of the cell cycle?

Answer 16

CKIs
Ex. INK4 family including p16, 15, 18 and 19
Ex. Cip/Kip families - p21, p27 and p57

Question 17

What Cdk-cyclin complex is present during G1 phase?

Answer 17

Cyclin D1 and Cdk4/6

Question 18

Which Cdk-cyclin complex is present during S phase?

Answer 18

Cyclin E and CDK2 (early)

Question 19

Which Cdk-cyclin complex is present during G2 phase?

Answer 19

Cyclin A and Cdk (early)

Question 20

Which Cdk-cyclin complex is present during M phase?

Answer 20

Cyclin B and Cdk1

Question 21

Which CKIs can inhibit cyclin D and Cdk4/6?

Answer 21

p16, p15, p18 and p19

Question 22

Which CKIs can inhibit the later cyclin-Cdk complexes of the cell cycle?

Answer 22

p57 —> p27 —> p21

Question 23

Describe the Ras pathway that leads to proliferation

Answer 23

Mitogen binds to receptor -> MAPK pathway -> activation of Myc gene -> leads to Rb phosphorylation -> increased E2F activity -> entry into S phase
Ex of an oncogene

Question 24

What occurs during the G2/M transition?

Answer 24

Activation of Cdk1/cyclin B at the G2/M boundary maintained by Cdc25
Complex then trans locates to the nucleus and initiates spindle assembly
Activated anaphase promoting complex (APC) destroys Cdk1 freeing cyclin B for degradation

Question 25

Describe the slow pathway of the G1 checkpoint

Answer 25

Involves stabilization of p53 and transcriptional upregulation of p21 which binds and inhibits cyclin D-Cdk4/6

Question 26

Describe the fast pathway of the G1 checkpoint

Answer 26

Acts via the activation of Chk2 and the inactivation of Cdc25 thus inhibitory phosphates of the Cyclin E/Cdk2 complex can no longer be removed

Question 27

Describe the G1/s transition and the role of Rab and E-Cdk2

Answer 27

Rb protein is normally bound to and inhibits E2F
E-Cdk2 complexes can drive the hyper phosphorylation of Rb which allows it to detach from E2F
E2F then trigger increased transcription of cyclin E-Cdk2 complexes which and stimulate their own expression further amplifying this process