Chapter 14, Problem 9STP

Summary Introduction

To analyze:

The effect of dimer formation after ultraviolet radiation on the structure of DNA molecule

Introduction:

High energy radiations are highly mutagenic. When radiation reaches the DNA, electrons absorb energy. The electrons escape the atom leaving behind free radicals. Free radicals react violently with other molecules including the DNA.

Answer to Problem 9STP

The adjacent thymine bases form dimers when exposed to UV radiation. This disrupts the structure of DNA and it is unable to replicate properly.

Explanation of Solution

The UV radiation from Sun does not cause free radicals as it has less energy than X-ray radiation. But UV radiation can cause adjacent thymine bases to bind to each other forming a dimer. The thymine bases form covalent bonds with each other disrupting the structure of DNA as thymine can no longer bind to adenine in complementary strand. This makes the DNA molecule “kink” and it is unable to replicate properly unless repaired.