Chapter 6.6 - Cell Cycle

Question 1

The Cell Cycle Groups (6)

Answer 1

Interphase

1. G0: resting. not actively dividing but cells are still working.
2. S Phase: DNA Synthase. Synthesis phase replication of chromosomes (10-12 hours to complete).
3. G2: Gap 2 growth and preparation for cell division.

Mitosis/M Phase
1. Cytokinesis and Mitosis

*entire cycle takes approximately 15-24 hours in humans. Once replication begins it must be completed.

Question 2

Mitosis

Answer 2

The process of cell division that produces identical daughter cells

Question 3

Replication of chromosomes

Answer 3

Occurs during S Phase. Chromosomes only “condense” during prophase, in which the sister chromatids separate, creating two new centromeres (identical daughter cells)

Question 4

Steps of Mitosis

Answer 4

1. G2 of Interphase
2. Prophase
3. Prometaphase
4. Metaphase
5. Anaphase
6. Telophase

Question 5

G2 of Interphase

Answer 5

• Chromosomes have duplicated

- Two centrosomes are formed in this phase

Question 6

Prophase

Answer 6

• Chromosomes have condensed

- Mitotic spindles form

Question 7

Prometaphase

Answer 7

• Fragments/fragmentation of nuclear envelope

- microtubules attach to newly formed kinetochore

Question 8

Metaphase

Answer 8

• Chromosomes align at the metaphase plate

- Centrosomes are at the opposite ends of the cell

Question 9

Anaphase

Answer 9

• Separation of sister chromatids

- Cell elongates

Question 10

Telophase

Answer 10

• Nuclear envelope on daughter nuclei reforms

- Cytokinesis soon follows

Question 11

Mitotic Spindle

Answer 11

• centrosomes and microtubules growing out of them

- they move chromosomes around and elongate cells

Question 12

Kinetochore

Answer 12

• where the microtubules attach to the chromosome pairs

- only way to do this is by getting rid of the nuclear envelope (re-forms during telophase)

Question 13

Cohesin

Answer 13

The protein that binds sister chromatids together. *during anaphase cohesion is degraded

Question 14

Metaphase and Microtubules important diagram

Answer 14

Kinetochore Microtubules: Chromatids move along these to the opposite end of the cell

Non-Kinetochore Microtubules: These overlap and allow motor proteins to walk along the opposite microtubule, elongating the cell, (region of overlap is reduced). This overlap of microtubules pushes the centrosomes apart

Question 15

Kinetochore and Non-Kinetochore Microtubules

Answer 15

Microtubules that either bind or do not bind to the kinetochore

Question 16

Motor proteins “walk” chromatids toward spindle poles

Answer 16

• Dinine walks toward centrosomes

- Microtubules disassemble behind it

Question 17

Cytokinesis (5 Steps)

Answer 17

• Divides up cell contents
• Contractile Ring (cleavage furrow) forms at the “metaphase plate”
• Ring made up of microfilaments (actin) and the motor protein myosin
• Myosin walks along the microfilaments, causing the ring to contract
• Cleavage furrow forms

Question 18

Cell Cycle Checkpoints diagram

Answer 18

G1: Commitment Stage; The cell is committed to dividing and dies if it doesn’t
G2: Ensures that replication is done. Spindle checkpoint (M checkpoint)

Question 19

Apoptosis

Answer 19

Controlled cell death

Question 20

Cyclin’s/CDK’s Regulate the Cell Cycle (3)

Answer 20

• Cyclin-dependent kinases (CDK) present throughout cell cycle but not active
• CDK’s activated by binding specific cyclin
• Cyclin concentration varies according to stage

Question 21

Cyclin diagram

Answer 21

Simply a regulatory protein that binds CDK

Question 22

Mitosis Promoting Factor Activity

Answer 22

• MPF only occurs during M phase
• Essentially just the active CDK/Cyclin
• CDK enzyme is present throughout the cell cycle, but its concentration and activity isn’t interchangeable
• problem questions in slide*