American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

What effect does PHA have on DNA synthesis?

1. It inhibits DNA synthesis

2. It causes a peak in DNA synthesis at 72 hours

3. It has no effect on DNA synthesis

4. It decreases the synthesis rate over time

The correct answer is: It causes a peak in DNA synthesis at 72 hours

PHA, or phytohemagglutinin, is a plant lectin that is widely used in laboratory settings for its ability to stimulate cell division, particularly in lymphocytes. When introduced into a culture, PHA acts as a mitogen, promoting the activation and proliferation of these cells. This leads to an increase in DNA synthesis as the cells prepare to replicate their genetic material in response to the stimulation. The peak in DNA synthesis typically occurs around 72 hours after the introduction of PHA. This timing correlates with the cell cycle progression where cells enter the synthesis phase (S phase) after being stimulated. During this period, an increase in DNA replication activity is observed as cells divide and multiply. Therefore, the correct answer highlights the dynamic role that PHA plays in enhancing cellular activities related to DNA synthesis, particularly within a specific timeframe after administration. In contrast, the other statements do not accurately depict the physiological effects of PHA on DNA synthesis. PHA does not inhibit DNA synthesis nor does it render DNA synthesis ineffective; instead, it actively promotes it. Additionally, it does not decrease the synthesis rate over time but rather facilitates an increase in this activity, leading to a peak around the noted time frame.