Question

Why does DNA molecule with a high G-C content have a higher boiling point?

Short answer

DNA with high G-C content has a higher boiling point due to more hydrogen bonds between G-C pairs, increasing stability.

Step-by-step solution

- Understand the DNA Structure

DNA is composed of four nucleotide bases: adenine (A), thymine (T), guanine (G), and cytosine (C). The bases are paired as A-T and G-C.

- Hydrogen Bonds in DNA

A-T pairs are joined by two hydrogen bonds, whereas G-C pairs are joined by three hydrogen bonds. Hydrogen bonds contribute to the stability of the DNA double helix.

- Compare the Number of Hydrogen Bonds

Since G-C pairs have three hydrogen bonds compared to the two hydrogen bonds of A-T pairs, the more G-C pairs present in the DNA, the more hydrogen bonds will exist.

- Boiling Point and Stability

The higher number of hydrogen bonds in DNA with a high G-C content makes the structure more stable and requires more energy (higher temperature) to break these bonds, resulting in a higher boiling point.

Key concepts

DNA Structure

DNA, or deoxyribonucleic acid, is the molecule that carries genetic instructions in all living organisms. It's composed of units called nucleotides. Each nucleotide consists of a sugar molecule, a phosphate group, and a nitrogenous base. There are four types of nitrogenous bases in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C). These bases pair specifically: adenine always pairs with thymine, and guanine always pairs with cytosine.

This base pairing forms the rungs of the DNA double helix ladder. The order of these bases encodes genetic information. The backbone of DNA, made of sugar and phosphate, holds the structure together while the base pairs are like steps holding the two strands of the helix together.

Hydrogen Bonds in DNA

In the DNA structure, hydrogen bonds form between the base pairs holding the two strands of the double helix together. A-T pairs form two hydrogen bonds while G-C pairs form three hydrogen bonds. Although hydrogen bonds are relatively weak compared to covalent bonds, they are essential for the stability of DNA.

The presence of three hydrogen bonds per G-C pair compared to two per A-T pair adds extra stability to the DNA double helix. This is because more energy is required to break three hydrogen bonds than two. Consequently, DNA regions with higher G-C content are more stable.

DNA Stability

The stability of DNA is crucial for its function in storing and transmitting genetic information. Stability is influenced by several factors, among which the hydrogen bonding between paired bases is significant.

Regions of the DNA with high G-C content are more stable because the triple hydrogen bonds in G-C pairs are stronger than the double hydrogen bonds in A-T pairs. This increased number of hydrogen bonds provides greater resistance to forces that can disrupt the DNA structure, such as heat (high temperature).

As a result, DNA with high G-C content has a higher boiling point. Boiling point in this context refers to the temperature at which DNA strands separate, or denature. More hydrogen bonds mean that more energy is required to denature the DNA, hence increasing its boiling point.