Nucleic Acids: Structure and Components

Nucleic Acids

Introduction to Nucleic Acids

Nucleic acids are essential biomolecules that store and transmit genetic information in living organisms. The two main types of nucleic acids are DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). These molecules are polymers made up of repeating units called nucleotides.

• DNA is the genetic material in most organisms and is responsible for heredity.

• RNA plays various roles in gene expression and protein synthesis.

Structure of Nucleotides

Each nucleotide, the building block of nucleic acids, consists of three components:

• Pentose Sugar: A five-carbon sugar. In DNA, this is deoxyribose; in RNA, it is ribose.

• Nitrogenous Base: A nitrogen-containing ring structure. There are two types:

  • Pyrimidines: Single-ring structures (e.g., cytosine, thymine in DNA, and uracil in RNA).

  • Purines: Double-ring structures (e.g., adenine and guanine).

• Phosphate Group: One or more phosphate groups attached to the 5' carbon of the sugar.

Nitrogenous Bases in DNA and RNA

The nitrogenous bases are classified as follows:

• Pyrimidines: Cytosine (C), Thymine (T, found only in DNA), and Uracil (U, found only in RNA).

• Purines: Adenine (A) and Guanine (G).

In DNA, the four bases are A, T, G, and C. In RNA, uracil (U) replaces thymine (T).

Base Pairing in DNA

DNA is typically double-stranded, with the two strands held together by hydrogen bonds between complementary bases:

• Adenine (A) pairs with Thymine (T) via two hydrogen bonds.

• Guanine (G) pairs with Cytosine (C) via three hydrogen bonds.

This complementary base pairing is essential for DNA replication and function.

Phosphodiester Bonds

Nucleotides are joined together by phosphodiester bonds, which link the 3' carbon of one sugar to the 5' phosphate of the next nucleotide. This forms the sugar-phosphate backbone of nucleic acids.

• Covalent bonds provide stability to the nucleic acid structure.

Summary Table: Components of DNA and RNA

Component	DNA	RNA
Pentose Sugar	Deoxyribose	Ribose
Nitrogenous Bases	A, T, G, C	A, U, G, C
Strands	Double-stranded (usually)	Single-stranded (usually)
Function	Genetic information storage	Protein synthesis, gene expression

Additional Information

• Chloroplasts and mitochondria also contain their own DNA, which is distinct from nuclear DNA. This is important for the endosymbiotic theory and inheritance of certain traits.

• Covalent bonds (specifically, phosphodiester bonds) are responsible for the stability of the nucleic acid backbone.

Additional info: Some content was inferred based on standard biology curriculum and context clues from the provided notes.