Lecture 6: Nucleotides and Nucleic Acids

Overview

• Last lecture in the biochemistry series, focusing on nucleotides and nucleic acids.
• Transition to molecular biology, covering DNA to RNA to protein processes.

Importance of Nucleic Acids

• Fundamental units of information storage (DNA) in the nucleus and mitochondria.
• Crucial for information transfer, setting the stage for understanding genetics.

Central Dogma of Molecular Biology

• Flow of genetic information: DNA → mRNA → protein.
• Key nucleic acid components: DNA, mRNA, tRNA, rRNA.

Nucleotide Structure

• Components: Carbohydrates (5-carbon pentose sugars), phosphate, nucleobases.
• Types of Sugars:
  • Ribose in RNA.
  • Deoxyribose in DNA (2-prime deoxyribose).
• Phosphates: Occur in DNA structure as phosphodiesters.
• Nucleobases:
  • Two major types: Purines (adenine, guanine) - two-ring structure.
  • Pyrimidines (cytosine, thymine/uracil) - one-ring structure.
  • Hydrogen bonding patterns are crucial for DNA structure (G-C has 3 bonds, A-T has 2).

Nucleosides vs. Nucleotides

• Nucleoside: Ribose + nucleobase.
• Nucleotide: Nucleoside + phosphate(s).

DNA Structure

• Polymers of nucleotides linked by phosphodiester bonds.
• Covalent Structure: Alternating sugar-phosphate backbone.
• Anti-parallel Strands: 5' to 3' orientation, allowing thermodynamic stability.
• Shargaff's Ratio: 1:1 ratio of purines to pyrimidines across all organisms.

Non-Covalent DNA Structure

• Double Helix Formation: Stability from hydrogen bonds between base pairs.
• Rosalind Franklin's Contribution: X-ray diffraction data helped deduce DNA structure dimensions.
• Watson and Crick: Model building guided by Franklin's and Shargaff's data.

DNA vs. RNA

• DNA: Deoxyribose, double-stranded, stable storage of genetic information.
• RNA: Ribose, single-stranded with varied structures, transient messenger.
• RNA types: mRNA, tRNA, rRNA—each with unique roles.

Nucleotide Functions Beyond DNA/RNA

• ATP and GTP: Energy carriers in metabolism.
• Cyclic AMP: Functions as a second messenger in signaling pathways.

Hydrogen Bonding and Stability

• Base Pairing: Purines pair with pyrimidines.
• Hydrophobic Interactions: Contribute to DNA stability.

DNA Computing

• Logic Gates: DNA used in computing for information storage and processing.
• DNA Origami: Structuring DNA for building nanoscale objects.

Summary

• Understanding nucleotide structure is foundational for further exploring molecular biology, genetics, and their applications.