Exam 4 - Cell Cycle slides

Question 1

In cell reproduction, some cells are differentiated and cannot divide:

Answer 1

Nerve cells, muscle cells, red blood cells

Question 2

Some cells have differentiated, but could divide again:

Answer 2

Liver cells, lymphocytes

Question 3

Some cells continue to divide:

Answer 3

Epithelial cells, stem cells, hematopoietic stem cells => red and white blood cells.

Question 4

What does the cell cycle consist of?

Answer 4

G1 -> S -> G2 -> Mitosis (M-phase)

Question 5

What does interphase consist of?

Answer 5

G1 phase (organelle duplication, highly active metabolism), S phase (DNA duplication), and G2 phase (Highly active metabolism, Exit to Mitosis controlled by cyclinB1/CDK1 (MPF) levels.

Question 6

Describe G1 Phase.

Answer 6

Gap 1 phase

1. Cell cycle phase that follows immediately after exit from mitosis.
2. aka Post-mitotic phase
3. For many cells: major period of cell growth during its lifespan.
4. Synthesis of new organelles: great amount of protein synthesis and a high rate of metabolism in the cell.

Question 7

What happens during G1 when cells don’t divide anymore?

Answer 7

These cells are typically arrested at the end of G1 => called G0 phase. e.g. Nerve cells

Question 8

Describe S phase.

Answer 8

Synthesis phase

1. Cell cycle phase that follows after completion of G1 phase.
2. DNA is replicated here
3. Precise and accurate DNA replication is necessary to prevent genetic abnormalities (which often lead to cell death or disease)

Question 9

What is the G1/S transition?

Answer 9

A major checkpoint in the regulation of the cell cycle.

Question 10

What are the key control factors for S phase?

Answer 10

Cyclins and cyclin dependent kinase (CDKs)

Question 11

In eukaryotes, the regulatory pathways during S phase are:

Answer 11

Highly conserved.

Question 12

What do Cyclins do?

Answer 12

1. Control the progression of cells through the cell cycle by activating cyclin-dependent kinase (CDK) enzymes.
2. Cyclins alone have no enzymatic activity, but have binding sites for some substrates and target the CDKs to specific subcellular locations.
3. Cyclins, when bound with the dependent kinases (e.g. p34 (cdc2)) or cdk1 proteins, form the maturation-promoting factor (MPF).

Question 13

Describe the G2 Phase.

Answer 13

1. Pre-mitotic phase
2. Period of rapid cell growth and protein synthesis => cells get ready for mitosis.
3. In vertebrate cells, the G2/M DNA damage checkpoint consists of an arrest of the cell in G2 (may or may not be p53 dependent).

Question 14

DNA damage signals cause what?

Answer 14

Activation of the transcription factor p53.

Question 15

What is p53?

Answer 15

A tumor suppressor protein aka the guardian of the genome because of its role in conserving stability by preventing genome mutation.

Question 16

When does the end of G2 phase occur?

Answer 16

When a threshold level of active cyclin B1/CDK1 complex (MPF) has been reached.

Question 17

What happens during prophase?

Answer 17

1. Chromosomal material condenses to form compact mitotic chromosomes. Chromosomes are seen to be composed of two chromatids attached together at the centromere.
2. Cytoskeleton is disassembled, and mitotic spindle is assembled.
3. Golgi complex and ER fragment. Nuclear envelope disperses.

Question 18

What happens during prometaphase?

Answer 18

1. Chromosomal MTs attach to kinetochores of chromosomes.

2. Chromosomes are moved to spindle equator.

Question 19

What happens during metaphase?

Answer 19

1. Chromosomes are aligned along metaphase plate, attached by chromosomal MTs to both poles.

Question 20

What happens during anaphase?

Answer 20

1. Centromeres split, and chromatids separate.
2. Chromosomes move to opposite spindle poles.
3. Spindle poles move farther apart.

Question 21

What happens during telophase?

Answer 21

1. Chromosomes cluster at opposite spindle poles.
2. Chromosomes become dispersed.
3. Nuclear envelope assembles around chromosome clusters.
4. Golgi complex and ER reforms.
5. Daughter cells formed by cytokinesis.