Cell Cycle

Question 1

Function of the Cell Cycle (4)

Answer 1

• reproduce and pass genetic info
• DNA is replicated
• DNA distributed to 2 identical daughter cells
• growth with division

Question 2

Phases of Cell Cycle

Answer 2

• G1 (Gap 1) – generalized growth
• S (Synthesis) – DNA replication
• G2 (Gap 2) – preparation for segregation
• M (Mitotic) – segregation of chromatids

Question 3

Mitosis Phases

Answer 3

Prophase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 4

Prophase

Answer 4

• nuclear envelope breaks down

- chromosomes condense

Question 5

Metaphase

Answer 5

• chromosomes align at metaphase plate

Question 6

Anaphase

Answer 6

• sister chromatids pulled towards spindle poles

Question 7

Telophase

Answer 7

• chromosomes de-condense

- reformation of nuclei

Question 8

Budding Yeast - S. cerevisiae

Answer 8

• cell cycle stage by size of bud

- long G1 phase

Question 9

Fission Yeast - S. pombe

Answer 9

• elongation of ends
• formation of septum
• long G2 and M phase

Question 10

G2 - M Transition in S. pombe

Answer 10

• loss of Cdc2 activity = can’t enter M phase

Question 11

Cdc2

Answer 11

• cyclin dependent kinase

- activity regulated by amount of cyclin present

Question 12

Protein Families Regulate Cell Cycle

Answer 12

• kinases
• phosphates
• cyclin

Question 13

Mitosis Promoting Factor (MPF)

Answer 13

• heterodimer of CDK + mitotic cyclin

- formed at late G2

Question 14

Cyclin Regulation

Answer 14

• cyclins activates CDKs
• 4 classes of cyclin (G1, G1/S, S, M)
• cyclin regulated at transcription + ubiquitin

Question 15

Polyubiquination

Answer 15

• addition of Ub to a protein signals for protein to be degraded by proteasome
• cyclins targeted for destruction ubiquitination (controlled by SCF ubiquitin ligases)

Question 16

Regulate MPF Activity

Answer 16

• addition or removal of phosphate group on CDK
• prevent premature activation
• Wee1 (inactive)
• Cdc25 and CAK (active)

Question 17

Wee1

Answer 17

• kinase to phosphorylates CDK = INACTIVE
• remains in G2
• prevent premature activation
• CDK inhibitory kinase

Question 18

Cdc25

Answer 18

• phosphatase to remove phosphate group from CDK = ACTIVE
• exit G2
• activating phosphatase

Question 19

CAK

Answer 19

• kinase to phosphorylate CDK = ACTIVE

Question 20

Active MPF Uses

Answer 20

Phosphorylation

• chromosome condensation
• disassemble nuclear envelope
• interphase microtubule disassembly
• block vesicular traffic

Question 21

Exit Mitosis

Answer 21

• MPF inactivate at Anaphase
• cyclin degraded by polyubiquitination
• using Anaphase-Promoting Complex/Cyclosome (APC/C)
• recognizes destruction box in cyclin

Question 22

Mitotic Cyclin Levels in Cell Cycle

Answer 22

• Metaphase = high activity
• Anaphase = APC/C + polyubiquitination (degraded in proteasome)
• Telophase = low activity

Question 23

S Phase Entry

Answer 23

• phosphorylation of S-phase inhibitor (by G1/S cyclin)
• prevents premature initiation
• SCF ubiquitin ligase degrades inhibitor
• activates S cyclin

Question 24

Cell Cycle Process (6)

Answer 24

1) G1/S CDKs activate + phosphorylate S-phase inhibitor
2) SCF ubiquitin ligase degrades inhibitor –> S-phase CDKs
3) SCF ubiquitin ligase degrades S cyclins
4) Cdc25 + CAK activate CDK –> CDK + M cyclin = MPF
5) Metaphase + Anaphase
6) APC/C degrades M cyclin