The Cell Cycle

Question 1

What is mitosis?

Answer 1

- Cells create an exact copy of themselves
RAG
- Regenerate cells and tissues
- Asexual reproduction
- Growth

Question 2

What is meiosis?

Answer 2

Sexual reproduction of an organism

Question 3

What are the phases in the cell cycle?

Answer 3

IPPMAT
Interphase:
- G1 phase
- G0 phase
- S phase
- G2 phase

M phase:

• Prophase
• Prometaphase
• Metaphase
• Anaphate
• Telophase
• Cytokinesis

Question 4

What happens during G1 phase?

Answer 4

• After mitosis
• Human cells have 46 unduplicated chromosomes
• Cell grows, makes proteins and organelles
• Centrosome (and its two centrioles) duplicate
• Check that nutrients and environment are favourable for duplication

Question 5

What happens during G0 phase?

Answer 5

• Cells stop dividing if they do not have the resources to continue

Question 6

What happens in S phase?

Answer 6

• Before mitosis
• DNA is replicated by DNA polymerase
• Human cells have 46 duplicated chromosomes
• Each duplicated chromosome is made up of two sister chromatids joined at the centromere

Question 7

What happens during G2 phase

Answer 7

• Cell continues to grow

- Check that all DNA is duplicated and undamaged

Question 8

What happens during prophase?

Answer 8

• Mitotic spindle forms in the cytosol: microtubules extend from the centrosomes
• Chromatin becomes densely compacted
• Nucleolus disappears

Question 9

What happens during pro metaphase?

Answer 9

• Nuclear envelope fragments
• Some spindle microtubules attach to the kinetochore at the centromeres
• Microtubules from opposite poles pull on chromosomes

Question 10

What happens during metaphase?

Answer 10

• Chromosomes align on the metaphase plate with sister chromatids on each side
• Check that all kinetochores are properly attached to the spindle

Question 11

What happens during anaphase?

Answer 11

• Sister chromatids pulled apart by microtubules
• Move towards opposite poles of the cell
• Other microtubules push the poles further apart

Question 12

What happens during telophase?

Answer 12

• Cell elongates
• Chromosomes decondense, nuclear envelope and nucleolus reform
• Cytokinesis begins

Question 13

What happens during cytokinesis

Answer 13

• Division of the cytoplasm

Animal cells:

• Cleavage furrow caused by internal microfilament contractile ring
• Parent cell pinches into two daughter cells

Plant cells:

• New cell wall is deposited by vesicles fusing within the parent cell
• Parent cell is internally divided into two daughter cells

Question 14

How do prokaryotes reproduce?

Answer 14

By binary fission

Question 15

How do viruses reproduce?

Answer 15

• Dependent on host for replication

- Viral genome can take over the host’s protein-making and other metabolic machinery

Question 16

What happens when the cell cycle escapes control?

Answer 16

• Non-disjunction: failure of the chromosomes to separate properly
• Can cause aneuploidy: having more or less chromosomes than normal
• Many tumours are aneuploid (usually too many chromosomes)
• Cancer is caused by uncontrolled cell growth due to failure of cell cycle regulation

Question 17

How does cell cycle regulation fail?

Answer 17

• Accidentally

- Mutations in cell cycle control proteins