Gujarat BoardEnglish MediumSTD 11 ScienceBIOLOGYCell Cycle and Cell Division1 Mark
Question
Describe the events taking place during interphase.
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Answer
The interphase is divided into three further phases:
i. $\mathbf{G}_1$ phase (Gap 1): The $G_1$ phase corresponds to the interval between mitosis and initiation of DNA replication. During the $G_1$ phase, the cell is metabolically active and continuously grows but does not replicate its DNA. The cells which divide frequently have a shorter $G_1$ phase, whereas the cells which divide infrequently have a longer $G_1$ phase.
ii. S phase (Synthesis): The S or synthesis phase marks the period during which DNA synthesis or replication takes place. During this time, the amount of DNA per cell doubles. If the initial amount of DNA is denoted as 2 C , then it increases to 4 C . However, there is no increase in the chromosome number. If the cell had diploid or 2 n number of chromosomes at $\mathrm{G}_1$, even after the S phase, the number of chromosomes remains the same, i.e. 2 n . The S phase in most eukaryotic cells lasts for 6 to 8 hours. When the $S$ phase begins, the cell must undergo mitosis.
iii. $\mathbf{G}_2$ phase (Gap 2): In animal cells, during the S phase, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm. During the $G_2$ phase, proteins are synthesised in preparation for mitosis while cell growth continues. The $\mathrm{G}_2$ phase in most cells lasts for 2 to 5 hours. Some proteins formed in $\mathrm{G}_2$ phase cause condensation of chromosomes to initiate mitosis.
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