Class notes for Chapter 6 Cell Divisions AS Level Biology A OCR

Cell Divisions:
• Cell Cycle
• Mitosis
• Meiosis
• The Organisation and Specialisation of Cells
• Stem Cells

, The Cell Cycle
The cell cycle describes
periods of cellular division,
followed by periods of
cellular growth. One
parent cell divides to form
either two or four
daughter cells (mitosis and
meiosis respectively).
For single cellular
organisms, this is their
entire life cycle.




Growth 1 phase (40%):
- Proteins are replicated during semi-conservative replication.
- The cell increases in size.
- These new proteins are used to build new organelles.

Growth 1 checkpoint:
Checks for cell size, nutrients, growth factors and DNA damage

Synthesis phase (39%):
- DNA replication/synthesis in the nucleus.

Growth 2 phase (19%):
- The cell increases in size.
- Energy stores are increased.
- The duplicated DNA is checked for errors.

Growth 2 checkpoint:
- Checks for cell size, DNA replication and DNA damage

Metaphase:
- Mitosis (nuclear division)
- Cytokinesis (cytoplasmic division)

Metaphase/spindle assembly checkpoint:
Checks that chromosomes are correctly attached to spindle fibres.