MICROANATOMY

Detailed explanation-1: -During S phase, replication increases the DNA content of the cell from 2n to 4n, so cells in S have DNA contents ranging from 2n to 4n. DNA content then remains at 4n for cells in G2 and M, decreasing to 2n after cytokinesis.

Detailed explanation-2: -During the S phase, the chromosomes enter a relaxed state that allows the enzyme DNA polymerase to access the DNA double helix inside each chromosome. Replication begins when helicase enzymes unzip various locations along the chromosome, separating the two complementary strands of DNA.

Detailed explanation-3: -DNA replicates in the S phase of the cell cycle and initiates at specific regions in the DNA sequence known as DNA replication ‘origins’. A number of proteins participate in DNA replication and the process is subject to scrutiny by cell surveillance mechanisms called cell cycle checkpoints.