Question

The correct sequence of phases of cell cycle is?

A. $M \to {G_1} \to {G_2} \to S$
B. ${G_1} \to {G_2} \to S \to M$
C. $S \to {G_1} \to {G_2} \to M$
D. ${G_1} \to S \to {G_2} \to M$

Answer 1

The phases in which a cell moves from one division to the next are called the cell cycle. Cell cycle is divided into two stages called (i) Interphase-the time of preparation for cell division, and (ii) Mitosis (M phase)-the real stage of cell division.

Complete Answer:
The eukaryotic cell cycle can be divided into interphase and the M phase. The interphase constitutes the longest stage in the cell cycle. It is further divided into ${G_1}$, $S$ and ${G_2}$ phases.

${G_1}$ phase refers to the time between the mitotic stage and the initiation of DNA replication. The cell is metabolically active during this phase and grows continually but DNA replication does not occur.

$S$ or synthesis Phase is the stage where the synthesis or replication of DNA occurs. The number of DNA per cell doubled during this period. The number of chromosomes however does not increase. In the ${G_2}$ phase, the synthesis of proteins takes place in preparation for mitosis, while the growth of cells continues.

The M phase begins with the nuclear division which corresponds to the separation of daughter chromosomes, and ends with cytoplasm division. The interphase, though known as the resting phase, is the stage where the cell prepares for division in an organized way by undergoing both cell growth as well as DNA replication.

Thus, the correct answer is option D i.e., ${G_1} \to S \to {G_2} \to M$.

Note: Some adult animal cells do not seem to exhibit division while many other cells occasionally undergo division to replace cells lost due to injury or cell death. These cells that do not undergo further division exit the ${G_1}$ phase to enter an inactive stage of the cell cycle known as the quiescent or ${G_0}$ stage.