DNA and RNA Lecture Notes

Introduction to DNA

• DNA (Deoxyribonucleic Acid)
  • Most complex molecule in existence
  • Stores genetic information and dictates cellular activities
  • Contains 6 billion-letter code that provides assembly instructions for organisms
• DNA Length & Scale
  • DNA from a single cell, if unraveled, would be longer than the lecturer (up to the Sun 600 times if all cellular DNA is linked)
  • Contains trillions of cells in the human body

Structure of DNA

• Components of a Nucleotide
  • A five-carbon sugar (Deoxyribose)
  • A phosphate group
  • One of four nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
• Double Helix Structure
  • DNA exists as a pair of molecules bonded together
  • The structure resembles a twisted ladder (double helix)
• Backbone Formation
  • Sugar and phosphate groups form the twin backbone
  • Backbones run in opposite chemical directions (5' to 3' and 3' to 5')
• Base Pairing Rules
  • Adenine pairs with Thymine (A-T)
  • Guanine pairs with Cytosine (G-C)
  • Pairs are bonded by hydrogen bonds

DNA Replication

• Replication Process
  • Takes place continuously as cells divide
  • Enzymes involved: DNA Helicase (unwinds the helix), DNA Polymerase (adds nucleotides to growing strand)
• Leading and Lagging Strands
  • Leading strand is synthesized continuously in the 5' to 3' direction
  • Lagging strand is synthesized in short fragments (Okazaki fragments)
• Error Correction
  • DNA Polymerase has proofreading capabilities
  • Ensures minimal errors during replication (1 in 10 billion nucleotides)
• Role of Primase and Ligase
  • Primase lays down RNA primers
  • Ligase joins Okazaki fragments

RNA (Ribonucleic Acid)

• Structure and Function
  • Single-stranded molecule
  • Contains Ribose sugar (one more oxygen than deoxyribose)
  • Uses Uracil (U) instead of Thymine (T)
• Types of RNA
  • mRNA (messenger RNA): carries genetic code from DNA to ribosomes
  • tRNA (transfer RNA) and rRNA (ribosomal RNA)
• RNA in Protein Synthesis
  • Crucial role in translating DNA instructions into proteins

Historical Context and Discoveries

• Early Discoveries
  • DNA discovered in 1869 by Friedrich Miescher
• Structure Discovery
  • Rosalind Franklin’s use of X-ray diffraction confirmed DNA’s helical structure
  • James Watson and Francis Crick built the first model using Franklin’s data
• Nobel Prize
  • Nobel Prize awarded to Watson and Crick but not to Franklin (posthumously disqualified)

Summary

• DNA is the fundamental molecule that carries genetic information and enables heredity

• RNA plays pivotal roles in gene expression and protein synthesis

• Understanding DNA’s structure and replication processes highlights its complexity and importance to life

• For further questions or discussions, students can visit the course forum on Facebook or Twitter.