Cell Division

Question 1

What are all the phases of the cell cycle?

Answer 1

• Interphase (95%, G1, S, G2)
• Mitosis (nucleus splits)
• Cytokinesis (cytoplasm splits)

Question 2

What occurs in G1, S and G2?

Answer 2

G1 and G2 - Organelles replicate, cell size increases, protein synthesis and respiration
Synthesis - DNA replication

Question 3

Where are the checkpoints and what to they check for?

Answer 3

G1 checkpoint - End of G1. Checks cell size and DNA damage. If there is, cell goes into G0 phase
G2 checkpoint - DNA replication error, cell size etc.
Spindle fibre checkpoint - During metaphase in mitosis. Checks spindle fibres are attached properly so DNA is spread evenly

Question 4

What happens during G0 and what are the possible reasons for it?

Answer 4

• Cell leaves cell cycle
• Differentiation - specialised cells can’t divide
• DNA damage
• Senescent cells - as we age, some cells reach max number of division

Question 5

What is the difference between centromeres and centrioles?

Answer 5

Centriole - Organelle that makes spindle fibres in the cell
Centromere - Structure of chromosomes that links sister chromatids together

Question 6

Describe mitosis

Answer 6

• Before mitosis can occur, DNA in the nucleus is replicated during interphase. Each chromosome is converted into two identical DNA molecules called chromatids
  Prophase - DNA coil and condense to form chromosomes and become visible. Nuclear membrane breaks down
  Metaphase - Chromosomes are moved by spindle fibres to form a plane in the centre of the cell called the metaphase plate.
  Anaphase - Centromeres divide, chromatids are separated and pulled to opposite ends of the cell
  Telophase - Chromatids have reached the poles and are called chromosomes. 2 new sets of chromosomes assemble at each pole and nuclear envelope reforms

Question 7

What happens in prophase 1?

Answer 7

• Homologous chromosomes pair up (bivalent)
• Crossing over leads to genetic variation as alleles are swapped

Question 8

What happens in metaphase 1?

Answer 8

• Homologous chromosome pairs/bivalents will go to the equator and line up
• Independent assortment leads to genetic variation as the maternal or paternal chromosomes can end up facing either pole

Question 9

What happens in anaphase 1?

Answer 9

• Homologous chromosomes are pulled to opposite poles
• No separation of centromere and chromatids stay joined

Question 10

Where is there genetic variation in meiosis 2?

Answer 10

• Metaphase 2
• Independent assortment of sister chromatids

Question 11

What are 3 stem cell potencies?

Answer 11

Totipotent - Differentiate into any type of cell
Pluripotent - Can form all tissue types but not whole organisms. Present in early embryos
Multipotent - Can only form a range of cells within a certain type of tissue