Lecture on DNA and RNA

LO:

1. Griffith’s experiment which discovered the process of bacterial transformation and the transforming principle

2. Avery, MacLeod and McCarty experiment which identified DNA as the transforming principle

3. Hershey-Chase experiment showing that the genetic material of phage T2 is DNA

4. Discovery of the Double Helical Structure of DNA by Watson & Crick and Franklin & Wilkins.

5. Nucleotide structure

6. Purine and pyrimidine base structure and Watson Crick Base Pairing

7. Structure of DNA and RNA and the key difference between ribose and deoxyribose

8. A, B and Z forms of DNA

Hard shizzzzz

• the different experiments and the orders and such

Introduction

• Basic introduction to DNA and RNA.
• Discuss key experiments that identified DNA as genetic material.
• Structure and replication process of DNA.

Key Experiments

Griffith's Experiment (1928)

• Studied Streptococcus pneumoniae.
• Two strains: Rough (non-pathogenic) and Smooth (pathogenic) in mice.
• Discovered bacterial transformation.
• Heat-killed Smooth strain mixed with Rough strain killed mice.
• Conclusion: Transforming principle from dead bacteria converts non-pathogenic to pathogenic.

Avery, McLeod, and McCarty (1944)

• Identified DNA as the transforming principle.
• Removed lipids, proteins, polysaccharides; only DNA remained active.
• Used DNAse to confirm loss of transformation ability.
• Demonstrated DNA changes organism properties but not accepted as genetic material universally.

Hershey-Chase Experiment

• Used bacteriophage T2 to show DNA is genetic material.
• Labelled DNA with 32P and protein with 35S.
• Found 32P (DNA) inside cells, proving DNA is genetic material.

Discovery of DNA Structure

• Watson, Crick, Franklin, Wilkins (1953) discovered double helix.
• X-ray diffraction showed helical structure with repeating units (3.4 Å between base pairs, 34 Å per helical turn).
• Chargaff's Laws: Pyrimidines = Purines, T = A and C = G.

DNA Structure

• Nucleotides: Sugar, nitrogenous base, phosphate group.
• Purines: Adenine, Guanine. Pyrimidines: Cytosine, Thymine (DNA), Uracil (RNA).
• Base Pairing: A-T (2 hydrogen bonds), C-G (3 hydrogen bonds).
• DNA strands are anti-parallel.
• Major and minor grooves for interaction.

Forms of DNA

• B-DNA: Right-handed helix, 10 base pairs per turn.
• A-DNA: Right-handed, more compact.
• Z-DNA: Left-handed, zigzag structure.

DNA Denaturation and Renaturation

• Double helix can be denatured (heated) and renatured (cooled).
• Important for genetic techniques like PCR.

RNA

• Single-stranded, contains uracil instead of thymine.
• Three types: mRNA (messenger), rRNA (ribosomal), tRNA (transfer).

tRNA Structure

• Cloverleaf structure with base pairing.
• Carries amino acids to ribosome during translation.

Conclusion

• Break for 10 minutes before discussing DNA replication.