Module 2, section 6: Cell division and cellular organisation.

What are the four parts of the cell cycle , and describe them.

1. G1 checkpoint: Checks for chemicals needed for respiration, and checks cellular damage.

2. Synthesis: DNA material is produced, and cells grows.

3. G2 checkpoint: DNA is checked for damage. if okay, cell undergoes mitosis.

4. M phase: Mitosis and cytokinesis.

How are chromosomes structured? Describe what sister chromatids are, and explain why there are two chromatids.

Two chromatids joined together by a centromere.

Sister chromatids are two identical chromatids, and there are two because of replication in mitosis.

Describe the stages of mitosis.

Prophase: Chromosomes condense. Centrioles move to opposite ends of the cell, forming the spindle. Nuclear envelope dissolves.

Metaphase: Each chromosome attaches to the centriole via their centromere, and line up on the spindl.

Anaphase: Centromeres divide, and spindle contracts, pulling chromatids to opposite poles

Telophase: Chromatids reach opposite ends and become chromosomes again. Nuclear envelope forms around both nuclei.

What happens at the metaphase checkpoint?

Cell checks that chromosomes are correctly lined up on the middle and attached to spindle fibres.

What is a homologous chromosome?

A pair of two of the same chromosome, inherited one from each parent.