2.1.6 Cell division, cell diversity and cellular organisation

Question 1

What are the two phases of the cell cycle

Answer 1

1. Interphase
2. Mitotic (division) phase

Question 2

What occurs during interphase?

Answer 2

• DNA is replicated + checked for errors in the nucleus
• Proteinsynthesis occurs in the cytoplasm
• Mitochondria grow + divide, increasing in number in the cytoplasm
• Chloroplast grow + divide in plant + algal cell cytoplasm, increasing in number
• Normal metabolic processes of cells occur

Question 3

Outline what occurs during the three stages of interphase

Answer 3

1. G1 = the first growth phase: proteins from which organelles are synthesised are produced + orgnalles replicate. The cell increases in size
2. S = synthesis phase: DNA is replicated in the nucleus
3. G2 = the second growth phase: the cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors

Question 4

What are the two phases of the mitotic phase?

Answer 4

1. Mitosis- the nucleus divides
2. Cytokinesis- the cytoplasm divides and two identical daughter cells are produces

Question 5

What is G0?

Answer 5

The name given to the phase when the cells leave the cell cycle, either temporarily or permenantly

Question 6

Why might a cell enter G0?

Answer 6

1. Differentiation
   A cell that becomes specialised (differenciated) is no longer able to divide + will carry out its function indefinitely, not entering the cell cycle again
2. DNA damage
   If a cell’s DNA is damaged it cannot divide as it is no longer viable. So, it enters a period of permenant arrest (G0).

A few types of cells that enter G0 can be stimulated to go back into the cell cycle. Eg, lymphocytes in immune response

Question 7

How is the cell cycled regulated?

Answer 7

By 3 checkpoints:
1. G1 checkpoint
2. G2 checkpoint
3. Spindle assembly/metaphase checkpoint