DNA and Genetic Experiments

Griffith Experiment

• Involved dead mice and recovery of the S strain.
• Initially inconclusive about whether DNA or protein was the genetic material.

Hershey and Chase Experiment

• Used bacteriophages (viruses that infect bacteria).
• Utilized radioactive sulfur (protein) and phosphorus (DNA) to track genetic material.
• Confirmed that DNA is the genetic factor.

Discovery of DNA Structure

• Watson and Crick discovered DNA structure, supported by Rosalind Franklin.
• Chargaff's Rule: Percentage of adenine (A) equals thymine (T), cytosine (C) equals guanine (G).
• Each species has the same percentage of A, T, C, G.

DNA Replication

• Meselson and Stahl: DNA replication is semi-conservative (one old strand, one new strand).
• Incorrect hypotheses included fully conservative and dispersive replication.
• Semi-conservative replication illustrated by complementary strand synthesis using Chargaff's Rule.

Structure of Nucleic Acids

• DNA and RNA are nucleic acids.
• DNA found in nucleus, nucleoid region, or mitochondria/chloroplasts.
• RNA found throughout the cell; aids in relaying messages from DNA.
• Nucleotide structure: phosphate, five-carbon sugar, nitrogenous base.
  • DNA: adenine, thymine, cytosine, guanine
  • RNA: uracil instead of thymine
• Purines: Adenine and Guanine (larger, two rings)
• Pyrimidines: Thymine and Cytosine (smaller, one ring)

DNA Replication Enzymes

• Helicase: Breaks hydrogen bonds, unzips DNA.
• Topoisomerase: Prevents supercoiling.
• Primase: Creates RNA primer for DNA polymerase attachment.
• DNA Polymerase III: Adds new nucleotides to 3' end of new strand.
• Lagging vs. Leading Strand: Okazaki fragments on lagging strand; continuous on leading strand.
• DNA Ligase: Glues Okazaki fragments together.
• DNA Polymerase I: Replaces RNA primers with DNA.
• SSB Proteins: Keeps DNA strands apart during replication.

Eukaryotic vs. Prokaryotic Replication

• Eukaryotes: Linear DNA, multiple origins of replication.
• Prokaryotes: Circular DNA, single origin of replication.

Telomerase and Aging

• Telomerase adds telomeres to protect chromosome ends.
• Active in stem and cancer cells; inactive in most somatic cells.
• Telomere shortening linked to aging.

DNA Mutation and Repair

• DNA Polymerase: Proofreads and corrects errors during replication.
• Mismatch Repair: Corrects bulges/divots from mismatched pairs.
• Nucleotide Excision Repair: Fixes thymine dimers often caused by UV light.

Types of Mutations

• Point Mutations: Substitution, insertion, deletion.
  • Silent: No change in protein.
  • Missense: Changes one amino acid.
  • Nonsense: Creates stop codon.
• Frameshift Mutations: Insertions/deletions causing shifts in the reading frame.

Miscellaneous

• DNA is organized as a double helix (right-handed model).
• Sugars and phosphates form the backbone; bases form the rungs of the ladder.
• Telomeres consist of non-coding repeated sequences to protect DNA ends.

Visualization

• Understanding of replication, enzymes, and mutations through diagrams and videos available online for further exploration.