Question

Which cell cycle phase would NOT progress if a lack of nutrients prevented cell growth?

a.Cytokinesis

b. S phase

c. Metaphase

d.G2 phase

Answer 1

S phase

If nutrients are not available then the cell cycle will arrest in the G1 phase and not progress occur towards the S phase. This we can prove by adding growth factors. For example in the case of mammalian cells, removal of growth factors by removal of serum from culture medium arrest cell cycle in G0. Re addition of serum allows the cell to re-enter the cell cycle. When the arrest reversed by addition or supply of growth factors or removal of inhibitors leading to the progression of S phase.

During the G1 phase synthesis of RNA and protein for S phase will occur. When cells have reached an appropriate size and have synthesized the required proteins, they enter the cell cycle by traversing a point called START in case of yeast and restriction point in the case of mammals. Then the cell is committed to cell division

The first step towards successful cell division is the entry into the S phase.

All other options are wrong because cell begins mitosis after the second Gap phase. G2 phase is the second Gap phase important preparatory phase for the M phase. Therefore, the nutrient availability arrest cell in G1 not in G2 and will arrest progression towards the S phase of the cell cycle.

Metaphase is a stage in mitosis. The chromosome will arrange on the metaphase plate and attached to the microtubule via kinetochore. If the alignment is not proper then the cell cycle will halt at M phase. Proper alignment of the chromosome is the factor that activates the checkpoints and halts the cell cycle here not nutrients.

Cytokinesis is the division of cytoplasm. After mitosis, cytokinesis occurs by forming contractile ring in case animals it is independent of nutrient availability.