Mitosis and Cell Cycle

Question 1

Do all cells keep dividing?

Answer 1

In multicellular organisms, not all cells keep their ability to divide. Eukaryotic cells that do retain the ability to divide show a cell cycle.

Question 2

Explain what happens during interphase of the cell cycle?

Answer 2

1. S phase – DNA replicates semi-conservatively leading to two sister chromatids
2. G1 and G2 – Number of organelles and volume of cytoplasm increases; protein synthesis; ATP content increased
3. Order is G1, S, G2

Question 3

Explain what happens during mitosis?

Answer 3

Explain what happens during mitosis?

1. Parent cell divides = two genetically identical daughter cells, containing identical/exact copies of DNA of the parent cell.
2. Stages - ‘PMAT’

Question 4

Prophase: (1)

Answer 4

1. Chromosomes condense, becoming shorter and thicker = appear as two sister chromatids joined by a centromere
2. Nuclear envelope breaks down and centrioles move to opposite poles forming spindle network

Question 5

Metaphase: (2)

Answer 5

1. Chromosomes align along equator
2. Spindle fibres attach to chromosomes by centromeres

Question 6

Anaphase: (3)

Answer 6

1. Spindle fibres contract, pulling sister chromatids to opposite poles of the cell
2. Centromere divides

Question 7

Telophase: (4)

Answer 7

1. Chromosomes uncoil, becoming longer and thinner
2. Nuclear envelope reforms = two nuclei
3. Spindle fibres and centrioles break down

Question 8

Cytokinesis (not a stage of mitosis):

Answer 8

The division of the cytoplasm, usually occurs, producing two new cells

Question 9

Describe the importance of mitosis in the life of an organism?

Answer 9

1. Parent cell divides to produce 2 genetically identical daughter cells for…
2. Growth of multicellular organisms by increasing cell number
3. Repairing damaged tissues / replacing cells
4. Asexual reproduction

Question 10

Explain the appearance of cells in each stage?

Answer 10

1. Interphase→ no chromosomes visible (visible nucleus)
2. Prophase→ chromosomes visible but randomly arranged
3. Metaphase→ chromosomes lined up on the equator
4. Anaphase→ chromatids (in two sets) being separated to opposite poles by spindles, V shape shows sister chromatids have been pulled apart at their centromeres
5. Telophase→ chromosomes in two sets, one at each pole

Question 11

Describe the 2 types of tumours?

Answer 11

1. Malignant tumour – cancer – spreads and affects other tissues / organs
2. Benign tumour – non-cancerous

Question 12

Explain how cancer treatments are directed at controlling the rate of cell division?

Answer 12

1. Disrupt the cell cycle – cell division / mitosis slows – tumour growth slows
2. Prevent DNA replication → prevent / slows down mitosis
3. Disrupts spindle activity / formation → chromosomes can’t attach to spindle by their centromere → sister chromatids can’t be pulled to opposite poles of the cells → prevent/slow mitosis

Question 13

Give one advantage and one disadvantage of these drugs?

Answer 13

1. Drugs more effective against cancer cells because dividing uncontrollably / rapidly
2. Disrupt cell cycle of normal cells too, especially rapidly dividing ones e.g. cells in hair follicles

Question 14

Describe how prokaryotic cells replicate?

Answer 14

Binary fission:
1. Circular DNA and plasmids replicate (circular DNA replicates once, plasmids can be replicated many times)
2. Cytoplasm expands (cell gets bigger) as each DNA molecule moves to opposite poles of the cell
3. Cytoplasm divides
4. 2 daughter cells, each with a single copy of DNA and a variable number of plasmids

Question 15

Describe how viruses replicate?

Answer 15

Viruses don’t undergo cell division because they are non-living:
1. Attachment protein binds to complementary receptor protein on surface of host cell
2. Inject nucleic acid (DNA/RNA) into host cell
3. Infected host cell replicates the virus particles