Nucleotides are the building blocks of nucleic acids (DNA and RNA), carrying genetic information and serving key roles in metabolism (e.g., ATP, GTP).
Basic Structure
| Component | Definition | Example |
|---|---|---|
| Nucleoside | Base + (Deoxy)Ribose (sugar) | Adenosine, Guanosine |
| Nucleotide | Base + (Deoxy)Ribose + Phosphate | AMP, GMP, dATP |
- The phosphate group is linked via a 3′–5′ phosphodiester bond between sugars.
- The 5′ end bears a triphosphate, providing energy for bond formation.
Nitrogenous Bases
| Type | Bases | Structure | Mnemonic |
|---|---|---|---|
| Purines | Adenine (A), Guanine (G) | 2 rings | “Pure As Gold” |
| Pyrimidines | Cytosine (C), Uracil (U), Thymine (T) | 1 ring | “CUT the Pyramid” |
Key Facts
- Thymine is found only in DNA; Uracil in RNA.
- Methylation of uracil → thymine.
- Thymine has a methyl group.
- C–G bonds (3 H-bonds) are stronger than A–T bonds (2 H-bonds).
Deamination Reactions
| Original Base | Deaminated Product |
|---|---|
| Cytosine | Uracil |
| Adenine | Hypoxanthine |
| Guanine | Xanthine |
| 5-Methylcytosine | Thymine |
Clinical Insight:
Deamination is a spontaneous mutation process. If not repaired, it can lead to transition mutations and contribute to cancer.
Amino Acids Required for Purine Synthesis
| Amino Acid | Role in Purine Synthesis |
|---|---|
| Glycine | Provides part of the purine ring |
| Aspartate | Nitrogen donor |
| Glutamine | Amino group donor |
Key Points to Remember
- Purines: A & G (2 rings)
- Pyrimidines: C, T, U (1 ring)
- Thymine = Methylated uracil
- C–G bonds stronger → ↑ DNA stability
- Purine synthesis requires Glycine, Aspartate, and Glutamine
🎯 Learning Objective
By the end of this session, students should be able to:
- Describe the structure and components of nucleotides, differentiate purines and pyrimidines, explain base-pair bonding, and identify key amino acids involved in purine synthesis—linking molecular principles to clinical contexts such as mutagenesis and DNA stability.
