Cells: Cell Cycle

Question 1

Perpetuation

Answer 1

• cells arise from pre-existing cells
• cell division leads to an increase in cell number
• cells must reproduce to ensure life continues
• all humans are formed from an original cell (zygote)
• DNA doubles before cell division because each new cell must have a copy of the genetic information from the original cell

Question 2

Cell Cycle

Answer 2

= the cycle of cell division and enlargement

• after being formed by cell division, a new cell enlarges by taking in water and synthesising new cell components (interphase)
  phases: Interphase (G1, S, G2), Mitotic Phase

Question 3

Interphase (G1)

Answer 3

“gap phase”

• cell organelles replicate
• cell grows
• cell accumulates energy as ATP, glucose & fat droplets for DNA replication

Question 4

Interphase (S)

Answer 4

“synthesis phase”

- DNA replicates

Question 5

Interphase (G2)

Answer 5

“growth phase”

- protein synthesis eg. enzymes

Question 6

Mitosis

Answer 6

• prophase
• metaphase
• anaphase
• telophase (+cytokinesis)

Question 7

Interphase

Answer 7

• G1
• S
• G2

Question 8

Mitosis (Prophase)

Answer 8

• nuclear membrane disintegrates
• nucleolus disappears
• spindle fibres form (microtubules)

Question 9

Mitosis (Metaphase)

Answer 9

• chromosomes pulled by spindle fibres and arrange at equator/metaphase plate
• sister chromatids arranged so that they face opposite poles

Question 10

Mitosis (Anaphase)

Answer 10

• sister chromatids move toward poles

- centromeres divide, spindle fibres shorten

Question 11

Mitosis (Telophase)

Answer 11

• nuclear membrane and nucleolus reappear
• chromosomes lose shape, form chromatin
• cytokinesis divides the cytoplasm equally; ensures the formation of two daughter cells (stem cell & differentiated cell)

Question 12

Checkpoints

Answer 12

= halt the cell cycle and wait for a specific signal, favourable size and environment

1. late G1 - restriction point “R”
   - signal = growth factors (bind to receptor molecules, induce changes in relay proteins, relay signal to the growth mechanisms in the nucleus)
   - effect = triggers growth, cell division, move to S
2. late G2
   - signal = cyclin + CDK = [MPF] increase
   - effect = G2 ends, mitosis begins
3. mitosis, after metaphase
   - signal = [MPF] decreases
   - effect = anaphase begins

Question 13

Binary Fission

Answer 13

= cell divison in prokaryotes

1. DNA untwisted, cut, enzymes replicate, two DNA double helices in circular loops
2. DNA loops attached to cell membrane
3. cell grows, membrane between loop expands
4. cell membrane pinches, forming 2 new cells

Question 14

Regulation - Internal Factors

Answer 14

- G1: nutrients, ATP, glucose, fat droplets

Question 15

Regulation - External Factors

Answer 15

• growth factors: G1
• hormones:
  …in plants, growth coordinated by cytokinins (root tips), auxins & gibberellins (stem tips)
  …in animals, 50+ hormones identified eg. erythropoietin stimulates RBC production
  …in humans, luteinising hormones (LH) & follicle stimulating hormone (FSH) control production of ovum & sperm.

Question 16

Uncontrolled Cell Division

Answer 16

• strong correlation between carcinogenesis (onset/development of cancer) and mutagenesis (change in DNA sequence - mutations)
• main agents responsible for mutagenesis:
  …chemicals (nucleotide sequence)
  …radiation (chromosome breaks)
  …viruses (addition of foreign DNA)
• cancer and the cell cycle:
  …checkpoints malfunctioning
  …growth factors not needed
  …cells produce their own growth factors