Biomolecules in the Cell > Nucleic Acids

Nucleic acids are large biological macromolecules that store and transmit genetic information in living organisms.

A nucleotide is the basic structural unit of nucleic acids, composed of a nitrogenous base, a pentose sugar, and a phosphate group.

A nucleoside consists of a nitrogenous base linked to a pentose sugar without a phosphate group.

A nitrogenous base is an organic molecule (purine or pyrimidine) that carries genetic information in nucleic acids.

DNA is a double-stranded nucleic acid that stores and transmits hereditary information and can replicate itself.

RNA is a single-stranded nucleic acid that helps in protein synthesis and information transfer.

Nucleic acids are large polymeric macromolecules (polynucleotides) found in the acid-insoluble fraction of living tissues. They constitute the genetic material of all living organisms.

• Discovery: Discovered and isolated from pus cells by Friederich Miescher in 1869.
• Types: There are two main types based on the sugar they contain: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).

Nucleic acids are polymers made of repeating monomeric units called nucleotides. Each nucleotide consists of three chemically distinct components:

A. Pentose Sugar (5-carbon monosaccharide):

• Deoxyribose: Found in DNA (ribose with one oxygen removed from C2).
• Ribose: Found in RNA.

B. Phosphoric Acid (Phosphate Group):

• Derived from H₃PO₄.
• It links with sugars to form the sugar-phosphate backbone of the polynucleotide chain.

C. Nitrogenous Bases (Heterocyclic Rings): Categorised into two types:

• Purines (double-ring): Adenine (A) and Guanine (G).
• Pyrimidines (single-ring): Cytosine (C), Thymine (T - found only in DNA), and Uracil (U - found only in RNA).

• N-glycosidic linkage: Connects a nitrogenous base to the 1'C of the pentose sugar to form a nucleoside.
• Phosphoester linkage: Connects a phosphate group to the 5'C OH of a nucleoside to form a nucleotide.
• 3'–5' Phosphodiester linkage: Joins two distinct nucleotides together to form a dinucleotide and subsequently a polynucleotide chain.

• Chargaff’s Rule (1950): In DNA, the amount of purines always equals the amount of pyrimidines. The base ratio (A+T / G+C) remains constant for a particular species.
• Watson & Crick Model: Proposed the double helix structure of DNA, resembling a twisted ladder where the rails are the sugar-phosphate backbone and the rungs are pairs of purine/pyrimidine bases.
• Directionality: A polynucleotide chain has a free phosphate moiety at the 5'-end of the sugar (5'-end) and a free OH group at the 3'C of the sugar (3'-end).

1. DNA: Acts as the blueprint of the cell, storing hereditary information to maintain genetic continuity between generations. It is unique because it can replicate itself.
2. RNA: Primarily responsible for transmitting genetic information from the nucleus to ribosomes for protein synthesis. It functions as a messenger (mRNA), an adapter (tRNA), a structural component (rRNA), and sometimes as a catalyst.
3. Medical/Legal Applications: Nucleic acid principles are used in DNA fingerprinting (personal identification, forensics), gene therapy, and diagnosing inherited diseases like sickle cell anaemia and haemophilia.

• Nucleic acids are biomacromolecules present in the acid-insoluble fraction and are responsible for the storage and transmission of genetic information (DNA and RNA).
• They are polynucleotides, formed by repeated units called nucleotides.
• Each nucleotide consists of three components: a nitrogenous base, a pentose sugar, and a phosphate group.
• Nitrogenous bases are of two types: purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil).
• The sugar present is either ribose (in RNA) or 2′-deoxyribose (in DNA).
• DNA is double-stranded and contains bases A, T, G, and C, while RNA is single-stranded and contains A, U, G, and C.
• DNA stores genetic information, while RNA plays a key role in protein synthesis and the expression of genetic information.