Eukaryotic Cell Cycle

Question 1

What does cellular replication produce?

Answer 1

Production of two daughter cells that are identical to the parent cell

Requires:

• Accurate duplication of chromosomes
• Precise segregation of chromosomes

Process is tightly regulated

Question 2

What is anneuploidy and what is it caused by?

Answer 2

Improper segregation of chromosomes causes aneuploidy (an abnormal number of chromosomes).

Aneuploidy can cause either an over-or under-representation of genes that can be either lethal or cause disease (e.g. cancer)

Question 3

What is the G1 phase?

Answer 3

Before a cell can divide, it must grow

• Metabolically active
• Comprises largest segment of the cell cycle
• Approximately 11 hours
• Exception: Early cell divisions of embryos proceed without a G1 or G2 phase, Cells become progressively smaller

Question 4

What is the S phase?

Answer 4

• Replication of the DNA
• Takes approximately 8 hours

Question 5

How many times does DNA replicate during the cell cycle?

Answer 5

Only one time

Question 6

What two enxymes is DNA replicaton regulated by?

Answer 6

Binding of MCM (minichromosome maintenance) helicase to

replication origins during late G1, which prepares the

ORC for initiating replication.

-Kinase activity during late

G1/S that prevents re-

initiation of replication

Question 7

What is G2 phase?

Answer 7

• Second growth phase
• Preparation for mitosis
• Takes approximately 4 hours

Question 8

What is the restriction point?

Answer 8

Commitment to Cell Cycle Progression

Restriction point – R (animal cells)

• Entry into the cell cycle is controlled by the availability of growth factors
• In the absence of growth factors, cells enter a quiescent state, G0
• When stimulated by growth factors, cells enter the cell cycle in G1

Question 9

How does growth factor signaling affect the cell cycle?

Answer 9

Links progression through the cell cycle to conditions in the cell’s environment

• Growth factor binding to its receptor initiates a signaling cascade leading to synthesis of Cyclin D
• If growth factors withdrawn before cell passes R, Cyclin D will be degraded and cell will enter G0
• If cell is already past R when growth factor is withdrawn, cell cycle will be completed

Question 10

What are cyclins?

Answer 10

• Cyclins bind to cyclin dependent kinases to regulate their activity
• Cyclin levels fluctuate during the cell cycle

Question 11

What CDK/Cyclin associates with early G1 to R?

Answer 11

CDK 4,6

Cyclin D

Question 12

What CDK/Cyclin associates with G1 to S transistion?

Answer 12

CDK2

Cyclin E

Question 13

What CDK/Cyclin associates with S phase?

Answer 13

CDK2

Cyclin A

Question 14

What CDK/Cyclin associates with the S to G2 transistion?

Answer 14

CDK1

Cyclin A

Question 15

What CDK/Cyclin associates with the G2 to M transistion?

Answer 15

CDK 1

Cylin B