Cell Division

Question 1

Why do we replicate cells and not grow them instead?

Answer 1

• if the cell grows, the surface area: volume ratio of the cell would be too low, so diffusion would be too low

Question 2

The cell cycle

Answer 2

1. Interphase: G1, S, G2
2. Mitosis: PMAT
3. Cytokinesis

Question 3

Interphase

Answer 3

• approximately 90% of cell cycle
• the cell increases in size and carries out normal cellular functions
• G1: cell makes enzymes and other proteins required fro growth, cell grows and copies all of its organelles
• S: the DNA in the nucleus replicates, after which each chromosomes consists of two identical sister chromatids
• G2: cell continues to grow and the new DNA is checked so that any errors can be repaired

Question 4

Phases of mitosis

Answer 4

1. Prophase
2. Metaphase
3. Anaphase
4. Telephase

Question 5

Prophase

Answer 5

• chromosomes condense and become visible
• nucleolus disappears
• centrioles move to opposite poles of the cell spindle fibres begin to form
• nuclear envelope breaks down - chromosomes are now ‘free’ in the cytoplasm
• spindle fibres begin to attach to the chromosomes at their centromeres

Question 6

Metaphase

Answer 6

• spindle fibres move the chromosomes so that they line up at the equator of the cell

Question 7

Anaphase

Answer 7

• centromeres divide and the chrmoatids move to the opposite poles of the cell because the spindle fibres shorten
• this requires energy in the form of ATP

Question 8

Telephase

Answer 8

• the 2 new sets of chromosomes assemble at each pole
• nuclear envelope begins to form, around each group of chromosomes
• nucleolus returns
• spinde fibres disintegrate

Question 9

Cytokinesis

Answer 9

• it involves the division of cytoplasm
• it produces two genetically identical daughter cells

Question 10

Why is mitosis important?

Answer 10

• growth: all cells produced are identical so organisms can grow using mitosis
• repair: all cells produced are identical so organisms can replace dead tissues using mitosis
• reproduction: some single-celled organisms reproduce by dividing into 2 identical daughter cells by mitosis

Question 11

Binary fission

Answer 11

1. Circular DNA molecule and plasmids are replicated. The circular DNA molecules attach to the cell surface membrane of the cell. The cell elongates
2. The cell surface membrane grows between the 2 circular DNA molecules and begins to pinch inwards. A new murein cell wall forms between the two circular DNA molecules
3. The cross wall forms completely and the cytoplasm and contents of the cell are divided into 2
4. Two daughter cells are formed, each with a single copy of the cirular DNA. The cells are nto always genetically identical because there may be a variable number of copies of the DNA

Question 12

Differences between mitosis in an animal cell and binary fission in a prokaryotic cell

Answer 12

• binary fission has no spindle fibres or centrioles
• no lining up of DNA at the equator
• DNA is circular, not linear
• 2 daughter cells not genetically identical

Question 13

How do viruses replicate

Answer 13

1. Virus uses attachment protein to bind to the surface of the host cell
2. Virus injects its genome into the host cell
3. Replication of viral DNA/ RNA and new viral proteins are made, forming new capsids

Question 14

Cancer

Answer 14

• occurs when cells divider uncontrollably by mitosis
• cancer normally happens when there is a mutation in a gene that controls mitosis
• these happen randomly but some thinks can increases the likelihood of these mutation
• cells with this mutation proliferate to form a tumor which can spread

Question 15

Cancer treatment

Answer 15

drugs used to treat cancer usually try to stop mitosis by either
- preventing DNA from replicating in S phase
- inhibiting the metaphase stage of mitosis by interfering with spindle formation