Nucleotides can be radiolabeled before they are incorporated into newly synthesized DNA and, therefore, can be assayed to track their incorporation. In a set of experiments, a student-faculty research team used labeled T nucleotides and introduced these into a culture of dividing human cells at specific times. Which of the following questions might be answered by using the method described?
A) How many cells are produced by the culture per hour?
B) What is the length of the S phase of the cell cycle?
C) How many picograms of DNA are made per cell cycle?
D) When do spindle fibers attach to chromosomes?

Question

Quizplus · Accepted Answer

By introducing labeled T nucleotides at specific times during the cell cycle, the team can track when the labeled nucleotides are incorporated into newly synthesized DNA. This will allow them to determine the length of the S phase, which is the period of DNA synthesis during the cell cycle. Therefore, option B is the correct choice.

The other options cannot be answered using the described method. Option A, the rate of cell production, could possibly be answered by measuring cell growth over time, but not by using labeled nucleotides. Option C, the amount of DNA produced per cell cycle, could possibly be determined by measuring total DNA content per cell, but not by using labeled nucleotides. Option D, the timing of spindle fiber attachment, is not related to the incorporation of labeled nucleotides and would require a different experimental approach.

Nucleotides Can Be Radiolabeled Before They Are Incorporated into Newly