1 Marks Question

Question

Describe the events taking place during interphase.

Vidyadip · Accepted Answer

The interphase is divided into three further phases:

G₁ phase (Gap 1): The G₁ phase corresponds to the interval between mitosis and initiation of DNA replication. During the G₁ phase, the cell is metabolically active and continuously grows but does not replicate its DNA. The cells which divide frequently have a shorter G₁phase, whereas the cells which divide infrequently have a longer G₁ phase.
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 2C, then it increases to 4C. However, there is no increase in the chromosome number. If the cell had diploid or 2n number of chromosomes at G₁, even after the S phase, the number of chromosomes remains the same, i.e. 2n. The S phase in most eukaryotic cells lasts for 6 to 8 hours. When the S phase begins, the cell must undergo mitosis.
G₂ 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 G₂ phase, proteins are synthesised in preparation for mitosis while cell growth continues. The G₂phase in most cells lasts for 2 to 5 hours. Some proteins formed in G₂ phase cause condensation of chromosomes to initiate mitosis.

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