How is the DNA of the cell affected during S-phase of the cell cycle ?

Options

A. DNA amount per cell is doubled
B. DNA amount per cell is halved
C. DNA amount per cell is tripled
D. DNA amount per cell remains the same

Answer

To understand how the DNA of the cell is affected during the S-phase of the cell cycle, we can break down the process into the following steps:

### Step-by-Step Solution:

1. **Definition of S-phase**: The S-phase, or synthesis phase, is a part of the cell cycle where DNA replication occurs. It is crucial for cell division, ensuring that each daughter cell receives an identical set of chromosomes.

2. **Initiation of DNA Replication**: During the S-phase, the process of DNA replication begins. The double-stranded DNA molecule unwinds and separates into two single strands at specific locations called replication forks.

3. **Formation of New Strands**: As the parental strands separate, new complementary strands are synthesized. This is done by the enzyme DNA polymerase, which adds nucleotides to the growing new strands based on the template provided by the parental strands.

4. **Doubling of DNA Content**: As a result of this replication process, the total amount of DNA in the cell doubles. Initially, there is one set of DNA (one complete set of chromosomes), and after the S-phase, there are two complete sets.

5. **Completion of S-phase**: By the end of the S-phase, each chromosome consists of two sister chromatids, which are identical copies of the chromosome connected at a region called the centromere. This prepares the cell for the next phase of the cell cycle, where the chromatids will be separated into two daughter cells.

### Conclusion:
During the S-phase of the cell cycle, the DNA of the cell is replicated, resulting in the doubling of the DNA content. Each chromosome is duplicated, leading to two identical sets of chromosomes in preparation for cell division.