Question 35 - Biological and Biochemical Foundations of Living Systems Practice Test for the MCAT

A simple calculation of the rate of spread of a pox virus (virion) led researchers at Imperial College London to a new insight. Virions communicate with other virions. The researchers observed that the radius of an approximately circular plaque of infected cells grew to 1.45 mm in just 3 days. They measured the distance between adjacent cells to be 0.037 mm to obtain the apparent time for the lytic cycle (from infection to lysis). They compared this time to the actual rate at which new virions are formed: 5 to 6 hours.

To account for this discrepancy between observed and predicted growth rates, the researchers examined the viral entry process and discovered that the actin protein on the host cell’s surface that provided the viral receptor was modified by attachment. They then found a mutant virus that did not modify the cell surface protein. The dependence of the growth of plaque radius on time for the wild type and mutant are shown in the graph.