03. Cell Cycle & Division — Checkpoints, Mitosis, & Meiosis

Question 1

What are the stages of the cell cycle?

Answer 1

• Interphase
  
  • G1: cell growth, normal metabolism, organelles duplicated
  • S: DNA replication
  • G2: cell growth, preparation for mitosis
• Mitosis
  
  • Prophase (chromosomes condense)
  • Metaphase (chromosomes align)
  • Anaphase (sister chromatids separate)
  • Telophase (chromosome decondense)
  • Cytokineses

Question 2

Why are there checkpoints in the cell cycle?

Answer 2

• Save energy and resources
• Internal control
• External control

Question 3

What are the cell cycle checkpoints?

Answer 3

1. Late G1
   
   1. Cell size (big enough)
   2. Environment (favourable conditions)
2. S-phase
   
   1. Is DNA replication proceeding (replication machinery functioning properly)
3. Late G2
   
   1. Has all the DNA been replicated correctly (only once)
   2. Cell size (big enough)
   3. Environment (favourable conditions)
4. Metaphase checkpoint
   
   1. Chromosome alignment on spindles

Question 4

How is variability introduced into the genome?

Answer 4

1. Sexual reproduction — random fertilization of 1n gametes.
2. Independent assortment of chromosomes in meiosis metaphase I.
3. Crossing over between non-sister chromatids in tetrads during metaphase I. (Creates recombinant chromosomes).

Question 5

What is meant by meiosis being a reduction division?

Answer 5

• The resulting cells have fewer chromosomes than the parent cells.
• DNA is replicated once, then divided: psuedo 4n (actually 2n) ⇢ psuedo 2n (actually n) (homologous chromosomes) — this is the reductional division.
• Homologs are separated: pseudo 2n (actually n) ⇢ n. This is an equational division.

Question 6

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