DNA Chapter 6: Nucleic Acid and Protein Synthesis

Importance

• Essential for AS syllabus; relevant for A2 studies.
• Knowledge of this chapter is crucial throughout A-level Biology.

Nucleic Acids

• Two types:
  • DNA: Deoxyribonucleic Acid
  • RNA: Ribonucleic Acid
• Both are polymers, composed of repeating monomers linked by covalent bonds.

Structure

• DNA: Typically two strands (exceptions discussed in A2, Chapter 18 on viruses)
• RNA: Usually a single strand
• Monomers (nucleotides) form DNA and RNA:
  • DNA is made of DNA nucleotides.
  • RNA is made of RNA nucleotides.

Nucleotides

• Basic structure:
  • Phosphate group
  • Pentose sugar (5 carbons)
  • Nitrogenous base
• Numbering of carbon atoms in pentose sugar:
  • Carbons numbered 1 through 5.
  • Important to remember five-carbon structure.

Nitrogenous Bases

• Purines: Larger, double ring structures (hexagon + pentagon)
  • Examples: Adenine (A), Guanine (G)
• Pyrimidines: Smaller, single ring structure (hexagon)
  • Examples: Cytosine (C), Uracil (U), Thymine (T)
  • Mnemonic: "CUT the pyrimidines" (Cytosine, Uracil, Thymine)

Differences between DNA and RNA Nucleotides

• DNA Nucleotides:
  • Pentose sugar: Deoxyribose (lacks oxygen on carbon 2)
  • Bases: Adenine, Guanine, Cytosine, Thymine
• RNA Nucleotides:
  • Pentose sugar: Ribose (has OH on carbon 2)
  • Bases: Adenine, Guanine, Cytosine, Uracil
  • Key Difference: DNA uses Thymine, RNA uses Uracil.

Identifying Nucleotides

• By observing:
  • Sugar type:
    • OH on carbon 2 = RNA (Ribose sugar)
    • Hydrogen on carbon 2 = DNA (Deoxyribose sugar)
  • Base present:
    • Thymine indicates DNA.
    • Uracil indicates RNA.
• Example scenarios help in identification based on sugar and base present.