Question

A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 4 picograms of DNA per nucleus. How many picograms would be found at the end of S and the end of G2?
a.) 16;16
b.) 8;8
c.) 8;16
d.) 4;8
e.) 4;4

Answer 1

Answer:

b: 8;8

Explanation:

Mitotic or meiotic cell division constitute the m phase of the cell cycle. At the end of the m phase, the new cells enter the interphase stage of the cell cycle. The interphase is further sub-divided into;

• the $G_0$ phase,
• the $G_1$ phase,
• the S phase; and
• the $G_2$ phase.

The $G_0$ phase is essentially a resting phase. Cells that do not need to divide except when necessary move into this phase after exiting the m phase.

Actively dividing cells enter the $G_1$ phase after exiting the m phase. Cell development and growth takes place. From there, the cells enter the S phase where DNA replication/synthesis takes place. The cells then enter the $G_2$ phase where proteins are synthesized in preparation for division or m phase.

At the S phase, the amount of DNA a cell carries is doubled but the chromosome number remains the same. For example, if a cell enters the S phase with 2 g of DNA containing 10 chromosomes, at the end of S phase, the amount of DNA would have come 4 g while the number of chromosomes will remain 10.

Hence, if the average amount of DNA in the assayed cells immediately after mitosis is 4 picograms, the amount would be 8 picograms at the end of S phase and will still remains 8 picograms at the end of $G_2$ phase.

The correct option is b.