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

Question 8

What do each of the cell cycle checkpoints check for?

Answer 8

1. G1= cell size, nutrients, growth factors + DNA damage
2. G2= check cell is ready for mitosis (cell size, DNA replication + DNA damage)
3. Spindle assembly checkpoint= chromosome attatchment to spindle

Question 9

What are the main stages in mitosis?

Answer 9

1. Prophase
2. Anaphase
3. Metaphase
4. Telophase
   (5. cytokinesis)

Question 10

Describe what occurs during prophase
1. Chromosomes
2. Chromatids
3. Nucleolus
4. Centrioles
5. Spindle fibres
6. Nuclear membrane

Answer 10

1. Chromosomes become visible as DNA coils/condenses
2. Each chromosome is made of 2 chromatids
3. Nucleolus disappears
4. Centrioles move to opposite ends of cell
5. Spindle fibres form from microtubles
6. Nuclear membrance breaks down

Question 11

Describe what occurs during metaphase

Answer 11

1. Centrioles reach poles and spindle is complete
2. Micro