Introduction to Cell Cycle- Lecture 51

Question 1

What are the techniques used to determine the number of cells undergoing various stages in the cell cycle?

Answer 1

mitotic index (mitotic cells/ cells undergoing division)
Ki-67 (proliferating cells)
flow cytometry (measure DNA content)

Question 2

How do you calculate the mitotic index?

Answer 2

number of mitotic cells
= ———————————-
total number of cells

Question 3

Where will the peaks for each phase in the cell cycle be located on a flow cytometer graph?

Answer 3

G1: about 100 DNA content (1x)
S: long peak inbetween 100 and 200
G2/M: small peak at about 200 DNA content (2x)

Question 4

What are the components of cyclin-dependent kinase and what do they do?

Answer 4

catalytic subunit (Cdk)
regulatory subunit (cyclin)
phosphorylate on serine/threonines immediately preceded by a proline residue

Question 5

What cyclin/ckd component(s) is/are associated with the G1 phase?

Answer 5

Cyclin D/ Cdk4 (early)
Cyclin D/ Cdk6 (early)
Cyclin E/ Cdk2 (late)

Question 6

What cyclin/ckd component(s) is/are associated with the S phase?

Answer 6

Cyclin A/ Cdk2

Question 7

What cyclin/ckd component(s) is/are associated with the G2/M phase?

Answer 7

Cyclin A/ Cdk1 (early G2)

Cyclin B/ Cdk1 (late G2/ early M)

Question 8

Cyclins are ______ transcriptionally, but are ______ by protein degradation via a ubiquitin-targeting mechanism.

Answer 8

upregulated

downregulated

Question 9

What does binding of cyclin to Cdk do?

Answer 9

1. provides part of the substrate binding site

2. induces conformational change that allows the substrate to access the catalytic site

Question 10

What is required for the activation of the Cdk-cyclin complex?

Answer 10

Cdk, cyclin, phosphorylation of a threonine residue (160) via a CAK

Question 11

Describe the pathway of cyclin-dependent kinase phosphorylation of Cdc25 and Wee1.

Answer 11

Cdk1 –(M-cyclin)–> inactive M-Cdk –Cdk-(activating kinase and Wee1)–> inactive M-Cdk (containing activating and inhibitory phosphate) –(phosphorylated Cdc25)–> active M-Cdk

Question 12

What are the inhibitors for the Cyclin-dependent kinases?

Answer 12

CIP class (P21, P22, P27)- all Cdks 
INK4 class (P15,P16, P18, P19)- binds only Cdk4 and Cdk6

Question 13

Increased cyclin is due to _______, whereas decreased cyclin is due to ______.

Answer 13

transciption

proteolysis

Question 14

What are the kinds of E3 enzymes?

Answer 14

SCF (SKP-Cullin-F box)

APC/C (anaphase promoting complex)

Question 15

Describe the properties of SCF enzymes.

Answer 15

ubiquitin ligase for cyclins important in the G1 to S transition (Cyclin D, Cyclin E)

Question 16

Describe the properties of the APC/C enzymes.

Answer 16

huge complex
ubiquitin ligase for the cyclins that are important for mitotic progression (Cyclin B)
requires activation via Cdh1 or Cdh20