Question

Draw structures to show how the sugar and heterocyclic base components of a nucleic acid are joined. What small molecule is formed?

Short answer

The sugar and base are joined by a glycosidic bond, forming a water molecule as a byproduct.

Step-by-step solution

Identify Components

A nucleic acid is made up of nucleotide units, each consisting of three parts: a sugar, a phosphate group, and a nitrogenous base (heterocyclic base). The sugar in DNA is deoxyribose, and the sugar in RNA is ribose.

Recognize the Sugar-Bonding Site

The sugar attaches to the nitrogenous base through its first carbon atom, often referred to as the 1' carbon.

Identify the Base-Bonding Site

The nitrogenous base connects to the sugar through one of its nitrogen atoms. For purines (adenine and guanine), it connects through the N9 atom. For pyrimidines (cytosine, uracil, and thymine), it connects via the N1 atom.

Draw the Chemical Linkage

The nitrogen atom of the base forms a glycosidic bond with the 1' carbon of the sugar. This bond is a covalent bond that results from a condensation reaction.

Establish the Reaction Output

The formation of the glycosidic bond expels a molecule of water (H₂O) as a byproduct, a characteristic of condensation reactions.

Key concepts

Nucleotide Structure

Nucleotides are the building blocks of nucleic acids, such as DNA and RNA. A nucleotide consists of three main parts:
1. A sugar molecule
2. A phosphate group
3. A nitrogenous base
These components play crucial roles in the structure and function of genetic material. The sugar and phosphate create the backbone, while the nitrogenous bases form the rungs of a ladder-like structure.
This structure is crucial for the stability and function of DNA and RNA, allowing them to store and transmit genetic information.

Glycosidic Bond

A glycosidic bond is a type of covalent bond that connects a sugar molecule to another molecule, here a nitrogenous base. In nucleic acids, this bond links the nitrogen atom within the base to the 1' carbon of a sugar.
This linkage is fundamental for the proper assembly and function of DNA and RNA structures. It stabilizes the attachment of the nucleotide components, supporting the integrity of the nucleic acid strands.

Condensation Reaction

The formation of a glycosidic bond between a sugar and a nitrogenous base occurs through a condensation reaction. This process involves the removal of a water molecule (H₂O).
This type of reaction helps build larger molecules from smaller ones by joining components, like forming nucleotide structures in nucleic acids. Condensation reactions often require energy input and specific enzymes to facilitate the bond formation.

Nitrogenous Base

Nitrogenous bases are key components of nucleotides, responsible for storing genetic information. They come in two types: purines and pyrimidines.

• Purines: Adenine (A) and Guanine (G) have a double-ring structure. They bond via the N9 nitrogen atom.
• Pyrimidines: Cytosine (C), Uracil (U), and Thymine (T) have a single-ring structure, linking through the N1 nitrogen atom.

In DNA, Adenine pairs with Thymine, and Cytosine pairs with Guanine. In RNA, Uracil replaces Thymine.

Deoxyribose and Ribose Sugars

In nucleic acids, the type of sugar distinguishes DNA and RNA. DNA contains deoxyribose, while RNA includes ribose. Deoxyribose lacks one oxygen atom compared to ribose.
This small difference significantly impacts the stability and structure of DNA and RNA. Deoxyribose contributes to DNA's double-helix stability. In contrast, ribose allows RNA to be more flexible, enabling diverse functionalities such as protein synthesis roles.