Lecture Notes: Nucleotides, Nucleosides, Purines, and Pyrimidines

Nucleosides vs. Nucleotides

• Nucleosides:

  • Composed of two components:
    • 5-carbon ribose sugar
    • Nitrogenous base

• Nucleotides:

  • Composed of three components:
    • 5-carbon ribose sugar
    • Nitrogenous base
    • Phosphate group

Nitrogenous Bases

• Five key nitrogenous bases:
  • Adenine (A)
  • Guanine (G)
  • Thymine (T)
  • Cytosine (C)
  • Uracil (U)

Purines vs. Pyrimidines

• Purines:

  • Adenine (A) and Guanine (G)
  • Nitrogenous bases with two rings

• Pyrimidines:

  • Thymine (T), Cytosine (C), and Uracil (U)
  • Nitrogenous bases with one ring

DNA vs. RNA

• DNA (Deoxyribonucleic acid):
  • Contains the bases: A, G, T, C
• RNA (Ribonucleic acid):
  • Contains the bases: A, G, C, U
  • Uracil (U) replaces Thymine (T)

Structural Differences

• Adenine vs. Guanine:
  • Guanine has a carbonyl group; adenine does not
  • Adenine has an aromatic ring (heterocyclic due to nitrogen atoms)
• Cytosine, Thymine, Uracil:
  • Thymine has a methyl group, uracil does not
  • Thymine and uracil have two carbonyl groups; cytosine has one

Stability and Aromaticity

• Aromatic Rings:
  • Highly stable due to alternating single and double bonds
  • Pi electrons move freely, contributing to aromaticity
• Resonance Structures:
  • Can form a stable aromatic ring
  • Charge separation occurs in some resonance structures

Key Concepts

• Aromatic rings contain alternating double bonds that enhance stability
• Purines have two rings; pyrimidines have one ring
• DNA includes thymine, RNA includes uracil

Conclusion

• Understanding these differences aids in distinguishing between nucleic acids and their components.