Question

DNA replication takes place in
A. G0 Phase
B. G1 Phase
C. G2 Phase
D. M Phase
E. S Phase

Answer 1

Hint: The sequence of events by which a cell duplicates its genome and synthesizes other cell contents and eventually divides into two daughter cells is termed as cell cycle. The cell cycle actually begins when the parental cell begins to divide and ends when one of these cells divides again into two cells. This division process, called M phase, involves two overlapping events, in which nucleus divides first and the cytoplasm second, M phase usually lasts less than an hour. Cells spend most of their time in the growth phase between divisions, called interphase.

Complete step by step answer: Phases of cell cycle-
1. Long undividing state
2. Shorter phase- nuclear division
3. still shorter phase- cytoplasmic division
Various phases of cell cycle are regulated by proteins – Cyclin & cyclin dependent protein kinases.
First checkpoint – G1 & S phase.
Second checkpoint – G2 & M phase.
Interphase
Newly formed cell- series of changes.
Synthetic/ S phase.
G 1 phase/ Gap 1
G 1 phase ,it is the interval between initiation of DNA replication and mitosis.
Frequently dividing cells – shorter G1 phase.
S phase / synthetic
S or synthesis phase is the phase when DNA replication takes place.
Centriole duplicates.
G2 phase/ Gap 2
RNAs & protein synthesis continues.
The G1 phase is marked by a gap between M phase and S phase. The M phase of the cell cycle is called when the division of nucleus as well as cytokines is divided and gives rise to daughter cells. G0 phase is the quiescent stage.
DNA Replication takes place in S Phase. So, the correct answer is option (E).

Note: Actually the cell cycle is very important, it is very useful for cell replication and cell reproduction in both eukaryotes as well as prokaryotes. The concept was first of all described by HOWARD AND PELE IN 1953. The cell cycle has two phases. In the interphase cell grows and replication takes place. In the mitotic phase there is the separation between replicated DNA and cytoplasmic content so that the cell divides.