DNA and RNA pt

Introduction to DNA and RNA

• Overview of the importance of DNA

• Visual comparison of peanut plants affected by larvae.

  • Left: Damaged by corn stalk borer larvae.

  • Right: Genetically engineered with a gene from Bacillus thuringiensis that produces a toxin.

• Central messages:

  • All organisms (viruses, bacteria, eukaryotes) share the same genetic material: DNA.

  • Genetic engineering allows humans to modify organisms by transferring DNA.

History of DNA

Key Experiments

• Frederick Griffith Experiment (1928)

  • Investigated Streptococcus pneumoniae using mice.

  • Rough strain (non-virulent) vs. Smooth strain (virulent).

  • Discovered "transforming factor" through heat-killed smooth strain mixed with live rough strain, resulting in mouse death.

• Avery, McCarty, McLeod Experiments (1930s-40s)

  • Followed up on Griffith's findings.

  • Isolated RNA, proteins, and DNA from bacteria.

  • Used enzymes to degrade each molecule:

    • RNA degradation: transformation continued.

    • Protein degradation: transformation continued.

    • DNA degradation: transformation ceased.

  • Conclusion: DNA is the transforming factor.

• Hershey-Chase Experiment (1952)

  • Used bacteriophages (viruses that infect bacteria) to determine genetic material.

  • Labeled proteins with sulfur and DNA with phosphorus to distinguish them.

  • Showed that only phosphorus (DNA) entered bacteria, proving that DNA is the hereditary material.

Discovering the Structure of DNA

Watson, Crick, Wilkins, and Franklin

• Watson and Crick credited for discovering the double helix structure of DNA

• Maurice Wilkins and Rosalind Franklin conducted x-ray crystallography to reveal the helical structure.

  • Franklin provided crucial data, although her contributions were overlooked.

• Erwin Chargaff found proportions of nucleotides:

  • A=T and C=G, now known as Chargaff's Rule.

  • Proportions consistent across different organisms.

• Watson and Crick utilized all previous research to model DNA:

  • Double helix structure with complementary bases (A-T and C-G).

Structure of DNA

Chromosomal Organization

• In eukaryotes:

  • DNA is wrapped around histone proteins to form chromatin, which condenses into chromosomes during cell division.

  • Characteristic X-shape observed during metaphase (replicated chromosomes).

• In prokaryotes:

  • DNA exists as a circular loop in the nucleoid region, not enclosed in a nucleus.

  • Circular DNA can have plasmids for additional genetic information.

  • Prokaryotic DNA is generally more compact with minimal non-coding regions (junk DNA).