Chapter 10_post

Genetics: A Conceptual Approach

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Chapter 10 DNA: The Chemical Nature of the Gene Dr. Ed Otto George Mason University
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Key objectives Review the scientific history that led to the elucidation of the structure of DNA Examine the chemical structure of nucleic acids (DNA and RNA) Understand some of the insights into key genetic processes made possible by an understanding of DNA’s structure
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History Leading to the Discovery of DNA’s Structure
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Characteristics of Genetic Material Before the 1950’s it was not widely accepted that genes are made of nucleic acids Whatever the nature of the genetic material, scientists knew it must possess 3 important characteristics: 1. Genetic material must contain complex information - must contain instructions for all the traits and functions of an organism - must have the capacity to vary, because different individuals differ in their genetic makeup - must be relatively stable, since most mutations are likely to be detrimental
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Characteristics of Genetic Material (Cont’d) 2. Genetic material must replicate faithfully - Each multicellular organism begins as a single cell which undergos many divisions during growth - At each cell division, the genetic instructions must be accurately transmitted to descendent cells 3. Genetic material must encode the phenotype - The genetic material (genotype) must have the capacity to “code for” (determine) traits (the phenotype) - The product of a gene is a protein; so there must be a mechanism for genetic instructions to be translated into the amino acid of a protein
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Early Studies of DNA 1868- Friedrich Miescher analysed nuclear material and discovered a novel substance that was slightly acidic and high in phosphorous - he called this material nuclein - this was later renamed _____________ 1887- widely recognized that the physical basis of heredity lies in the nucleus - Chromatin was shown to consist of protein and nucleic acid - But is was not clear whether protein or nucleic acid was the genetic material
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Early Studies of DNA 1900- Albrecht Kossel determined that DNA contains four nitrogenous bases: adenine (A), guanine (G), cytosine (C), and thymine (T) 1905- Aaron Levene discovered that DNA consists of a large number of repeating units called nucleotides, and that each nucleotide is composed of a sugar, phosphate, and nitrogenous base
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Early Studies of DNA Levene also incorrectly proposed that DNA consists of a series of four-nucleotide units, with each unit containing all four bases in a fixed sequence (tetranucleotide theory) Many scientists felt that this structure implied that DNA is not variable enough to be the genetic material So the prevailing view of the time was that it must be proteins that are the genetic material because, with its 20 different amino acids, protein structure could be highly variable
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Early Studies of DNA 1948- Edwin Chargaff measured the amount of the four bases in DNA - He found that the overall base composition in DNA from different organisms varied widely, disproving the
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This note was uploaded on 05/06/2010 for the course BIO 311 taught by Professor Otto during the Spring '10 term at George Mason.

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Chapter 10_post - Chapter 10 DNA: The Chemical Nature of...

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