Chapter 13, Problem 2Q

Summary Introduction

To review:

The number of starting points that a single deoxyribonucleic acid (DNA) molecule contains, based on the given diagram and whether the number is consistent with the results of the previous question.

Given:

The radioactivity inferred by the 3H-thymidine is shown for a small section of a single DNA molecule in the following figure. The DNA has been extracted from human cells, undergoing S phase (synthetic phase) after receiving pulse with 3H-thymidine for the last 4 hours of S phase.

Figure 1: The radioactivity of a small segment of DNA after receiving a pulse of 3H-thymidine.

Introduction:

The S phase or the synthesis phase is a part of the cell cycle where the cell synthesizes or duplicates its genetic material, that is, DNA. The S phase lasts for about 8 hours in humans. Whether the duplication has taken place or not, is detected by the incorporation of the radioactive thymidine.