Cell Cycle

Question 1

What are the phases of the cell cycle

Answer 1

• interphase which is made up of G1, S, G2
• the mitosis phase made up of
  Mitosis, cytokinesis

Question 2

Give a brief description of what occurs during interphase

Answer 2

• DNA is replicated and checked for errors in the nucleus
• protein synthesis occurs in the cytoplasm
• mitochondria grow and divide
• chloroplasts grow and divide
• normal metabolic processes occur eg. Respiration

Question 3

Describe each phase of interphase

Answer 3

• G1 phase: proteins from which organelles are synthesised are produced and organelles replicate, the cell increases in size
• S phase: DNA is replicated in the nucleus
• G2 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 reasons for a cell in G0 phase

Answer 4

• differentiation: a cell that becomes specialised to carry out a particular function is no longer able to divide, it will not re enter the cell cycle
• DNA may be damaged: this makes the cell no longer viable, a damaged cell cannot divide therefore enters G0
• As you age you increase the number of senescent cells, these are related to age related diseases such as Arthritis and cancer

Question 5

What 3 things must be ensured for the cell to divide, how are they checked

Answer 5

• the cell must be the right size
• replicated DNA must be error free
• the chromosomes must be in their correct position for during mitosis
• they are checked with 3 checkpoints

Question 6

Explain what happens at each checkpoint

Answer 6

• G1 checkpoint at the end of the G1 phase, checks if the cell is the right size, growth factors, nutrients and DNA damage
• G2 checkpoint at the end of the G2 phase checks whether DNA has been replicated without error, if the cell is correct size, and for any DNA damage
• spindle assembly checkpoint( metaphase checkpoint) this checks that the chromosomes are correctly attached to the spindle fibres