8. Nucleic Acids-Spring2025

Unit 1: Chemistry for Biology

Nucleic Acids

• Nucleotide Structure

  • Composed of a nitrogenous base + sugar = Nucleoside

  • Nucleoside + Phosphate = Nucleotide

  • NTP (Nucleoside Triphosphate): Monomers of RNA (G, A, U, CTP)

  • dNTP (Deoxynucleoside Triphosphate): Monomers of DNA (dG, dA, dT, dCTP)

  • 5’ and 3’ ends:

    • 5’ refers to the 5th carbon attached to a phosphate group.

    • 3’ refers to the 3rd carbon attached to a hydroxyl group.

Phosphodiester Bonds

• Formed between nucleotides, linking the phosphate of one nucleotide to the sugar of another.

ATP: Adenosine Triphosphate & Hydrolysis

Structure

• Sugar-phosphate backbone: forms the structural framework of nucleic acids.

• Hydrogen bonds between nitrogenous bases:

  • Adenine (A) pairs with Thymine (T)

  • Guanine (G) pairs with Cytosine (C)

Ends of DNA Strand

• 5’ end (Phosphate)

• 3’ end (Hydroxyl)

DNA Structure

• Double Helix Formation:

  • Discovered by James Watson and Francis Crick.

  • Complementary Base Pairing:

    • G pairs with C via hydrogen bonding.

    • A pairs with T via hydrogen bonding.

  • Antiparallel strands:

    • One strand runs 5’ to 3’ and the complementary strand runs 3’ to 5’.

    • Example: 5’-GATCATGC-3’ pairs with 3’-CTAGTACG-5’.

RNA Structure

• Single Stranded, can form variable secondary and tertiary structures.

• Types of RNA:

  • Ribosomal RNA (rRNA)

  • Transfer RNA (tRNA)

  • Messenger RNA (mRNA)

  • Other minor types.

Phosphodiester Bond Formation

• Occurs via nucleophilic attack and results in the formation of Inorganic Pyrophosphate (PPi) and Inorganic Phosphate (Pi).

Comparison: DNA vs RNA

Flow of Genetic Information

• Process:

  • Synthesis of mRNA in the nucleus

  • Movement of mRNA into cytoplasm via nuclear pore

  • Translation into protein at the ribosome.

Summary of Macromolecules