Question

In a DNA molecule, the double helix is held together by hydrogen bonds. How many hydrogen bonds are between an adenine (A) base and a thymine (T) base in DNA?

Short answer

There are 2 hydrogen bonds between an adenine (A) and a thymine (T) base in DNA.

Step-by-step solution

Identify the base pairing

In a DNA double helix, the nucleotide bases pair up in specific ways. Adenine (A) always pairs with Thymine (T), while Cytosine (C) pairs with Guanine (G).

Recall hydrogen bonding rules

Adenine (A) and Thymine (T) are connected by specific hydrogen bonds in DNA. Typically, each pairing type (A-T or C-G) has a characteristic number of hydrogen bonds that hold the bases together.

Determine hydrogen bonds for A-T

The connection between an adenine and a thymine base involves 2 hydrogen bonds. These bonds help stabilize the DNA double helix structure.

Key concepts

Hydrogen Bonds

Hydrogen bonds are a type of weak chemical bond that play a crucial role in the structure of DNA. Despite being weaker than covalent bonds, hydrogen bonds are essential for the stability and proper functioning of biological molecules.

• They occur when a hydrogen atom is attracted to a highly electronegative atom like oxygen or nitrogen.
• In the context of DNA, these bonds are responsible for holding the two strands of the double helix together.
• They allow for the specific pairing of nucleotide bases, ensuring accurate DNA replication and function.

Although each individual hydrogen bond is relatively weak, their collective strength across the DNA molecule provides the necessary stability for maintaining the DNA's structure. This stability is essential for the preservation and transmission of genetic information.

Adenine-Thymine Pairing

Adenine-thymine (A-T) pairing is a fundamental aspect of DNA's base pairing rules. In DNA, adenine (A), a purine base, always pairs with thymine (T), a pyrimidine base, through hydrogen bonds.

• Each A-T pair is stabilized by 2 hydrogen bonds.
• These specific bonds ensure that adenine pairs exclusively with thymine, maintaining the genetic coding integrity.
• This type of pairing is important for DNA replication as it ensures that the genetic information is copied accurately.

The hydrogen bonds between adenine and thymine are weaker than those between cytosine and guanine (which have three hydrogen bonds). This difference in bonding properties affects how tightly the DNA strands are held together.

DNA Double Helix Structure

The DNA double helix is a structural model that describes the shape of DNA in living organisms. It consists of two long strands, or "backbones," made of sugar and phosphate, running in opposite directions.

• These strands are connected by pairs of nucleotide bases, which form the "rungs" of the helix, somewhat akin to a twisted ladder.
• The specific base pairings, A-T and C-G, are crucial for the precise replication and function of DNA.
• The helical structure allows DNA to be packed tightly within the nucleus of a cell, while still being accessible for processes like transcription and replication.

The stability of the double helix is fully reliant on the specific pairing and interactions of the nucleotide bases, facilitated greatly by hydrogen bonds. This classic structure is key to understanding DNA function in genetics and biology.