Question

Which of the following statements about the cell cycle is/are correct? Choose all that apply. Which of the following statements about the cell cycle is/are correct? Choose all that apply. The cell cycle consists of 5 distinct phases: I, M, G1, S, and G2. All preparation for cell division occurs during M phase. At any stage of mitosis, a cell has twice as much DNA as in G1. Metabolically active cells can exit, and sometimes re-enter, the cell cycle. Extracellular conditions have no effect on cell cycle progression. Once the cell cycle has begun, it cannot be stopped without resulting in cell death.

Answer 1

Answer: The correct statements are-

1. At any stage of mitosis a cell has twice as much as DNA in G1.

2. Metabolically active cells can exit, and sometimes re-enter, the cell cycle.

Explanation :

1.. The cell cycle consists of 4 distinct phases - M phase which is the mitotic phase and the G1, S and G2 phase which together form the interphase. The interphase is preparatory phase wherein the cell grows in size, replicates the DNA etc. whereas the M phase is the one where events related to cell division takes place.

2. The cell has 2C amount of DNA during G1 but since the DNA replication takes place during S phase, the amount of DNA doubles up to 4 C and remains so in G2 and M phase until cytokinesis results in the formation of 2 daughter cells.

3. Sometimes, the metabolically active cells can exit the cell cycle and become quiescent until the conditions are favourable. When these quiescent cells recieve the right stimulus they can re enter the cell cycle.

4. Extracellular conditions such as nutrient availability, presence of certain mitogens, growth factors etc. do regulate the cell cycle progression. If any of these extracellular facotrs are limiting the cell cycle is arrested.

5. Once the cell cycle starts, it can be stopped without leading to cell death. When this happens it is known as cell cycle arrest. During this arrest several factors are assessed and if theire is need for repair of DNA then that also takes place. Once, the limitations are overcome or the repair is done, the cell cycle can then continue.