Question

The bases on opposite strands of DNA are said to be __________ to each other, which means the bases fit together specifically by hydrogen bonding to one another.

Short answer

The bases on opposite strands of DNA are said to be complementary to each other, which means the bases fit together specifically by hydrogen bonding to one another.

Step-by-step solution

Recall DNA base-pairing rules

In a DNA molecule, there are four types of nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T). These bases follow specific base-pairing rules, where Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C). This specific pairing between the bases is due to hydrogen bonding between them.

Identify the term used to describe the base-pairing relationship in DNA

The term used to describe how the bases on opposite strands of DNA fit together is that they are "complementary" to each other. This means that each base specifically pairs with its complementary base on the opposite strand, due to hydrogen bonding.

Answer

The bases on opposite strands of DNA are said to be complementary to each other, which means the bases fit together specifically by hydrogen bonding to one another.

Key concepts

Complementary Bases

When studying the structure of DNA, one is bound to encounter the term 'complementary bases'. These are pairs of DNA nucleotides that are attracted to each other due to the specific structure of their molecules. For DNA to function properly and to ensure genetic information is accurately passed on, these bases must pair correctly. The rule of thumb is reminiscent of a perfect dance partnership – for every 'Adenine' (A), there is a 'Thymine' (T) on the opposite strand, and for each 'Guanine' (G), a 'Cytosine' (C).

This partnership is not random; it's governed by the size and structure of the nitrogenous bases, which ensure that the DNA helix has a uniform width. Errors in this complementarity can lead to mutations, which sometimes have profound consequences for an organism. Understanding this principle is vital for grasping the basics of genetics and molecular biology.

Why Complementarity Matters

In DNA replication and transcription, the unerring match-up of these pairs is critical for the cell's ability to replicate and transcribe genetic information accurately. Without this, organisms may not function correctly, leading to various genetic disorders or diseases.

Nitrogenous Bases

At the heart of DNA structure are nitrogenous bases, essential chemical components that form the rungs of the twisted-ladder structure known as the double helix. There are four main types of nitrogenous bases in DNA: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). Each of these bases contains nitrogen atoms, which is why we refer to them as 'nitrogenous'.

These bases fall into two categories: purines and pyrimidines. Adenine and Guanine are classified as purines, which have a double-ring structure that makes them larger, while Cytosine and Thymine are pyrimidines, having a single-ring structure and being smaller.

Purines vs. Pyrimidines

The pairing of a purine with a pyrimidine within the DNA molecule maintains a constant width of the 'ladder', which is essential for the integrity of the DNA structure. A mix-up in this pairing can disrupt the helix and lead to errors in genetic information processing.

Hydrogen Bonding

Hydrogen bonding is a type of weak chemical bond that is critical in the structure of DNA. These bonds occur between the complementary bases of the DNA strands, holding the two strands of the helix together. Specifically, hydrogen bonds form between the nitrogenous bases: Adenine pairs with Thymine through two hydrogen bonds, and Guanine pairs with Cytosine through three hydrogen bonds.

The specificity of these bonds ensures that the DNA double helix is stable but also easy to separate during processes like DNA replication and transcription, where the double strand unwinds to allow the genetic information to be copied.

The Significance of Hydrogen Bonds in DNA

While hydrogen bonds are weak compared to covalent or ionic bonds, their collective strength across the millions of base pairs in a DNA molecule contributes significantly to the integrity and stability of the DNA structure. Furthermore, since they are weaker, enzymes can easily break them during the critical processes of DNA replication and transcription, without affecting the stronger covalent bonds that hold the individual nucleotides together.