Chapter 16 - The Molecular Basis of Inheritance

Chapter 16 - The Molecular Basis of Inheritance - Chapter...

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Chapter 16 Class Notes – The Molecular Basis of Inheritance – Page 1 Max Sauberman AP Biology – Mr. Schilp Chapter 16 The Molecular Basis of Inheritance Life’s Operating Instructions: In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of DNA, also known as deoxyribonucleic acid. DNA, the substance of inheritance, is the most celebrated molecule of our time, for its ability to encode for proteins, and direct the development of traits. Hereditary information is encoded in DNA and reproduced in all cells of the body. This DNA program directs the development of biochemical, anatomical, physiological, and behavioral traits. DNA is the genetic material: Early in the twentieth century, the identification of the molecules of inheritance loomed as a major challenge to biology. While Morgan’s group showed that genes are located on chromosomes, the two components of chromosomes (DNA and protein) became candidates for the genetic material. Initially, proteins were hypothesized as the genetic material, because they provide better variation, having twenty amino acids compared to only four nitrogenous bases. The key factor in determining the genetic material was choosing appropriate experimental organisms. The role of DNA in heredity was first discovered by studying bacteria and the viruses that infect them. Griffith’s Experiment: The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928, which gave sufficient evidence that DNA can transform bacteria. Griffith worked with two strains of bacterium: a pathogenic (bad) “S” strain, and a harmless “R” strain. When he mixed heat-killed remains of the pathogenic strain with living cells of the harmless strain, some living cells became pathogenic. He called this phenomenon transformation (the living R bacteria had been transformed into pathogenic S bacteria), now defined as a change in genotype and phenotype due to assimilation of foreign DNA. Discovering the transforming agent to be DNA: In 1944, Oswald Avery, Maclyn McCarty, and Colin MacLeod announced that the transforming substance was DNA.
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Chapter 16 Class Notes – The Molecular Basis of Inheritance – Page 2 Their conclusion was based on experimental evidence that only DNA worked in transforming harmless bacteria into pathogenic bacteria. Thus, without DNA, no transformation occurs. Therefore, DNA must be the hereditary material. Many biologists remained skeptical, mainly because little was known about DNA. Evidence that Viral DNA can program cells: More evidence for DNA as the genetic material came from studies of a virus that infects bacteria. Such viruses, called bacteriophages (or phages), are widely used in molecular genetics research. The Hershey-Chase Experiment:
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Chapter 16 - The Molecular Basis of Inheritance - Chapter...

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