Chapter 16 lecture

Chapter 16 lecture - Chapter 16: The molecular basis of...

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Chapter 16: The molecular basis of inheritance • Structure of DNA Historical events leading to the discovery of DNA as genetic materials and its structure. The characteristics of DNA structure. • Replication of DNA The mechanisms The players The challenges and solutions during DNA replication
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Do you have the answers? What does DNA stand for? What is the monomer of DNA? What are the four nitrogenous bases of DNA? Is DNA stable? What is double helix? What is anti-parallel? Is DNA double stranded or single stranded? What is DNA replication?
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DNA as genetic materials • The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928. • Griffith worked with two strains of a bacterium, one pathogenic and one harmless.
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Living S cells (control) Living R cells (control) Heat-killed S cells (control) Mixture of heat-killed S cells and living R cells Mouse dies Mouse dies Mouse healthy Mouse healthy Living S cells RESULTS EXPERIMENT
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DNA or protein • In 1944, Oswald Avery, Maclyn McCarty, and Colin MacLeod announced that the transforming substance was DNA. • Their conclusion was based on experimental evidence that only DNA worked in transforming harmless bacteria into pathogenic bacteria. • Many biologists remained skeptical, mainly because little was known about DNA.
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DNA is the genetic material • More evidence for DNA as the genetic material came from studies of viruses that infect bacteria. • Such viruses, called bacteriophages (or phages ), are widely used in molecular genetics research.
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Bacterial cell Phage head Tail sheath Tail fiber DNA 100 nm
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Biochemical studies • It was known that DNA is a polymer of nucleotides, each consisting of a nitrogenous base, a sugar, and a phosphate group. • In 1950, Erwin Chargaff reported that DNA composition varies from one species to the next. • This evidence of diversity made DNA a more credible candidate for the genetic material.
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Chargaff’s rules state that in any species there is an equal number of A and T bases, and an equal number of G and C bases. In human DNA: 30.3% A and T, 19.7% G and C In E.coli DNA: 26% A and T, 24% G and C.
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Cracking DNA structure • After most biologists became convinced that DNA was the genetic material, the challenge was to determine how its structure accounts for
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Chapter 16 lecture - Chapter 16: The molecular basis of...

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