Nucleic Acids: DNA & RNA — The Blueprint of Life

What Are Nucleic Acids?

Macromolecules storing and transmitting genetic information. Two types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).

Monomer: The Nucleotide

Each nucleotide = nitrogenous base + pentose sugar + phosphate group.

• Bases: Purines (Adenine, Guanine); Pyrimidines (Cytosine, Thymine in DNA / Uracil in RNA).
• Sugar: Deoxyribose (DNA) vs Ribose (RNA) — 2'-OH difference.
• Linkage: 3'-5' phosphodiester bonds → directional backbone (5'→3').

DNA: The Genetic Archive

• Double-stranded helix (antiparallel).
• Base pairing: A=T (2 H-bonds), G≡C (3 H-bonds).
• Stable, long-term storage. Nuclear (chromosomes) + mitochondrial.
• Replication: Semiconservative, high fidelity (proofreading).

RNA: The Versatile Worker

• Single-stranded (folds into complex 3D structures).
• Less stable (2'-OH → alkaline hydrolysis).
• mRNA: Carries coding sequence to ribosome.
• tRNA: Adapter — anticodon + amino acid.
• rRNA: Catalytic core of ribosome (ribozyme).
• Regulatory RNAs: miRNA, siRNA, lncRNA, circRNA — gene silencing, chromatin remodeling, scaffolding.

Central Dogma

DNA → (Transcription) → RNA → (Translation) → Protein. Reverse transcription (retroviruses, retrotransposons) adds RNA → DNA.

Why They Are Indispensable

1. Heredity: Faithful transmission across generations.
2. Protein synthesis: All cellular structure/function.
3. Gene regulation: Spatiotemporal control.
4. Catalysis: Ribozymes, RNase P, spliceosome.
5. Signaling: cAMP, cGMP, ATP (energy currency).
6. Defense: CRISPR-Cas (prokaryotic), RNAi (eukaryotic).
7. Biotechnology: PCR, sequencing, gene therapy, mRNA vaccines, synthetic biology.

Without nucleic acids, life as we know it cannot exist.