In which phase of the cell cycle do antimetabolites primarily exert their effects?

Antimetabolites primarily exert their effects during the S phase of the cell cycle, which is the phase where DNA synthesis occurs. These drugs mimic the natural substrates or intermediates involved in the synthesis of DNA, disrupting the process and preventing proper replication. This disruption can lead to the inhibition of cell division and ultimately cell death, making antimetabolites particularly effective against rapidly dividing cancer cells that are actively synthesizing DNA.

During the S phase, the cell is highly sensitive to these agents because they interfere with nucleotide metabolism and DNA replication processes. By targeting this specific phase, antimetabolites can achieve their therapeutic effects while minimizing damage to non-dividing cells.

In contrast, the other phases—G1, G2, and M—are not the primary targets for antimetabolites. G1 is involved in cell growth and preparation for DNA synthesis, G2 involves further preparation for mitosis, and M is the phase of actual cell division. While these phases are crucial for the overall cell cycle, antimetabolites specifically disrupt the DNA synthesis that occurs in the S phase.