Question

Which of the following phases is a pre-DNA synthesis phase?
A. G₁ phase
B. G₂ phase
C. S phase
D. Prophase

Answer 1

Hint: The sequence of events which results in the growth and division of a cell into 2 daughter cells is termed as cell cycle or cell-division cycle. It chiefly consists of 4 stages G₁ , S phase, G₂, and M phase.

Complete answer:
The sequence in which the events of the cell cycle proceeds is G1, S, G2 and M phase. In the G 1 phase the cell grows and begins to synthesize proteins and mRNA which facilitates the further steps leading to mitosis or cell division. The cell growth, protein and mRNA synthesis are very essential for the cell to enter the next phase which is the S phase in which the DNA synthesis begins leading to the formation of daughter cells in the subsequent phases.
Considering other options: B. G 2 phase also known as Gap 2 phase is the phase in which the cell undergoes rapid growth and protein synthesis so that the cell is well prepared to undergo mitosis and form daughter cells.
C. S phase is the phase after G 1 in which the cell is subjected to DNA replication and happens in G 1 and G 2 phases. Since the accurate replication of the genome is very important for successful cell division, this step is very crucial and well regulated.
D. Prophase is the first phase in mitosis in which the chromatin condenses into chromosomes. This is the step in which the nucleolus disappears, and the spindle fibers appear.

So, the correct answer is “Option A”.

Note:
In eukaryotic cells the stages of cell division are mainly classified into two: the interphase and mitotic phase. The interphase consists of 3 steps G 1, S and G 2 phases. While the mitotic phase comprises 4 phases mainly prophase, metaphase, anaphase and telophase.