01:119:115 Lecture Notes - Lecture 14: Thymine, Dna Replication, Nucleoside Triphosphate
General Biology
October 17, 2019
L14 — DNA
I. DNA is the Genetic Material
Chromosomes = DNA + Proteins!
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DNA: Deoxyribonucleic acid
4 nucleotides (Monomers)"
Proteins?!
#20 amino acids!
A. Frederick Griffith (1928)
Pneumonia vaccine!
1st to show evidence against protein hypothesis (genes was carried by protein)!
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Model: Streptococcus pneumonia — 2 strains!
Griffith’s Experiment
Smooth bacteria → mice = dead!
Rough bacteria → mice = alive!
Boiled bacteria → mice = alive!
Rough + boiled bacteria → dead!
Live smooth bacteria recovered from dead mice!
Demonstrated transformation: Change in genotype or phenotype due to assimilation
of external DNA!
What transformed the cells?"
DNA most likely carries the genes (not what Griffith thought)!
B. Avery, Macleod, McCarty (1944)
Lysed S cells, separated its components → Lipids, Carbs, Protein, DNA!
Tested for transformation # # # +#+ # +# +!
#####R# ← R#R# R# R → #S!
####!
Clear that DNA carries the gene, but people were not convinced!
C. Hershey and Chase (1952)
Used bacteriophage T2!
Bacteriophage: Virus that infects bacteria!
2 main components: DNA (or RNA) and Protein coat!
General Biology
October 17, 2019
Virus Life Cycle
Virus attaches to host cell → something enters cell → New viruses made → Cell lysis
→ virus released!
Experimental Design
Grow 1 virus population with radioactive sulfur (35S) [Protein radiolabeled]!
Grow second with radioactive phosphorous (32P) [DNA radiolabeled]!
Allow each to infect bacteria → Separate viruses from bacteria → Determine
location of radioactivity!
Results
35S present in separated viruses!
32P present in infected cells!
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Conclusion: Viruses transmit DNA; DNA carries genes!
SUMMARY!
Griffith — transformation!
Avery, Macleod, McCarty — DNA is the transforming material!
Hersey and Chase — virus DNA contains genes!
II. DNA Structure
A. Nucleotides: Monomers of nucleic acids
Each nucleotide contains: Phosphate group, Sugar, Nitrogenous base!
Basic building block of DNA!
Nitrogenous Bases
Purines: 2 rings# # Pyrimidines: 1 ring!
Adenine# # # Cytosine!
Guanine# # # Thymine!
DNA Strand