Nucleic Acids
DNA and RNA: Composition, Structure, and Function.
By chemca Team • Updated Jan 2026
Nucleic acids are long-chain polymers of nucleotides responsible for the transmission of genetic information and protein synthesis.
1. Chemical Composition
Hydrolysis Products
Complete hydrolysis of DNA/RNA yields three components:
- Pentose Sugar: $\beta$-D-2-deoxyribose (in DNA) or $\beta$-D-ribose (in RNA).
- Phosphoric Acid: $H_3PO_4$.
- Nitrogen Containing Heterocyclic Base:
- Purines: Adenine (A), Guanine (G).
- Pyrimidines: Cytosine (C), Thymine (T, only in DNA), Uracil (U, only in RNA).
2. Nucleoside & Nucleotide
Nucleoside: Sugar + Base (linked at $C_1'$).
Nucleotide: Sugar + Base + Phosphate (linked at $C_5'$).
Linkages:
1. Base is attached to Sugar via N-glycosidic linkage.
2. Nucleotides are joined together via Phosphodiester linkage (between $5'$ and $3'$ carbons of pentose sugar).
1. Base is attached to Sugar via N-glycosidic linkage.
2. Nucleotides are joined together via Phosphodiester linkage (between $5'$ and $3'$ carbons of pentose sugar).
3. Structure of DNA
Double Helix (Watson & Crick Model)
- Two nucleic acid chains are wound about each other and held together by Hydrogen bonds between bases.
- The strands are complementary (not identical).
- Base Pairing Rule:
- Adenine pairs with Thymine (A=T) with 2 H-bonds.
- Guanine pairs with Cytosine (G$\equiv$C) with 3 H-bonds.
4. Structure of RNA
Single Stranded
RNA is usually single-stranded. It contains Uracil (U) instead of Thymine (T).
Types of RNA:
- m-RNA (Messenger): Carries genetic code from DNA to ribosome.
- r-RNA (Ribosomal): Structural component of ribosomes.
- t-RNA (Transfer): Carries amino acids to ribosome for protein synthesis.
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