Question

Describe the types of bonds and attractions that link the monomers together in a DNA molecule.

Short answer

The monomers in a DNA molecule are nucleotides, consisting of a phosphate group, a deoxyribose sugar, and a nitrogenous base. Covalent bonds form within nucleotides between the sugar and phosphate group, as well as between adjacent nucleotides, creating a backbone of sugar-phosphate linkages. The double helix structure arises from hydrogen bonds between complementary nitrogenous base pairs, with adenine (A) pairing with thymine (T) and guanine (G) pairing with cytosine (C). \( A-T \) pairs form two hydrogen bonds, while \( G-C \) pairs form three hydrogen bonds, contributing to the DNA molecule's stability and specificity.

Step-by-step solution

Identifying the monomers in a DNA molecule

In a DNA molecule, the monomers are called nucleotides. Each nucleotide consists of three components: a phosphate group, a deoxyribose sugar, and a nitrogenous base. There are four types of nitrogenous bases in DNA: adenine (A), cytosine (C), guanine (G), and thymine (T).

Covalent bonds within a nucleotide

Within a nucleotide, there is a covalent bond between the sugar molecule and the phosphate group. This bond is formed due to the sharing of electrons between the sugar and phosphate group, providing stability within the nucleotide.

Covalent bonds between adjacent nucleotides

The adjacent nucleotides in the DNA molecule are held together by covalent bonds between the sugar of one nucleotide and the phosphate group of the next nucleotide, producing a backbone of sugar-phosphate linkages. These covalent bonds are also called phosphodiester bonds.

Hydrogen bonds between complementary bases

In order to form the iconic double helix structure, two DNA strands align in an antiparallel manner, with the nitrogenous bases facing each other. Complementary bases pairs, adenine (A) with thymine (T) and guanine (G) with cytosine (C), form hydrogen bonds between them. \( A-T \) base pairs have two hydrogen bonds, while \( G-C \) base pairs form three hydrogen bonds. These hydrogen bonds are responsible for the stability and specificity of the DNA molecule structure.

Key concepts

Nucleotide

A nucleotide is the basic building block of DNA. It consists of three key components: a phosphate group, a deoxyribose sugar, and a nitrogenous base. These nucleotides link together to form the long chains that make up the DNA molecule. Each nucleotide can be one of four types, based on its nitrogenous base: adenine (A), guanine (G), cytosine (C), or thymine (T).

These bases play a crucial role in storing genetic information, as the sequence of bases along the DNA strand encodes instructions for building proteins. Understanding nucleotides is essential, as they are the Lego blocks that build the entire structure of DNA.

Covalent Bonds

Covalent bonds are essential for stabilizing the DNA's structure. Within each nucleotide, a covalent bond forms between the deoxyribose sugar and the phosphate group. This is a strong bond created by the sharing of electrons between these two components, giving the molecule its stability.

Additionally, covalent bonds connect adjacent nucleotides, forming a chain. Specifically, the phosphate group of one nucleotide attaches to the sugar of the next. These connections are known as phosphodiester bonds. They create the backbone of DNA, linking nucleotides into a continuous strand.

Hydrogen Bonds

Hydrogen bonds are weaker than covalent bonds and are found between the nitrogenous bases of two DNA strands. These bonds are crucial in holding the two strands of the DNA double helix together.

Complementary bases pair specifically through hydrogen bonds: adenine (A) pairs with thymine (T) via two hydrogen bonds, and guanine (G) pairs with cytosine (C) through three hydrogen bonds. While individually weak, collectively, these bonds provide the necessary stability and ease of separation during processes like replication.

Complementary Base Pairing

Complementary base pairing refers to the specific pairing of nitrogenous bases across the two strands of DNA. Adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C). This is possible due to the precise nature of hydrogen bond formations between these base pairs.

Complementary base pairing is fundamental in maintaining genetic fidelity during DNA replication and transcription. Since each base can only pair with its complement, this mechanism ensures that the correct information is copied each time a cell divides. This specificity defines the double helix of DNA, which is essential for genetic inheritance.