Biology Chapter 16 Objectives

Biology Chapter 16 Objectives - Chapter 16 The Molecular...

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Chapter 16 The Molecular Basis of Inheritance DNA as the Genetic Material 1. Researchers originally thought protein was the genetic material because biochemists had identified them as a class of macromolecules with great heterogeneity and specificity of function, essential requirements for the hereditary material. Moreover, little was known about nucleic acids and their properties, which seemed too uniform to account for the multitude of specific inherited traits exhibited by every organism. 2. Frederick Griffith provided evidence that DNA is the genetic material through his study of a bacterium that causes pneumonia in mammals. He found that when he killed the pathogenic bacteria with heat and then mixed the cell remains with living bacteria of the nonpathogenic strain, some of the living cells became pathogenic. Furthermore, this new trait of pathogenicity was inherited by all the descendants of the transformed bacteria. The transformation was defined as a change in genotype and phenotype due to the assimilation of external DNA by a cell. Oswald Avery, Maclyn McCarty, and Colin MacLeod purified various types of molecules from the heat-killed pathogenic bacteria, and then tried to transform live nonpathogenic bacteria with each type; the transforming agent was the DNA. Alfred Hershey and Martha Chase used radioactive sulfur and phosphorus to trace the fates of the protein and DNA of T2 phages that infected bacterial cells. The experiments showed that DNA is the genetic material of a phage known as T2. Erwin Chargaff analyzed the base composition of DNA from a number of
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Biology Chapter 16 Objectives - Chapter 16 The Molecular...

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