Lectures 27 & 28 Molecular Basis of Inheritance

Lectures 27 & 28 Molecular Basis of Inheritance -...

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Unformatted text preview: Overview: Life’s Operating Instructions • In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA • DNA, the substance of inheritance, is the most celebrated molecule of our time • 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 (to some extent) behavioral traits DNA is the genetic material • Early in the 20th century, the identification of the molecules of inheritance loomed as a major challenge to biologists The Search for the Genetic Material: Scientific Inquiry • When T. H. Morgan’s group showed that genes are located on chromosomes, the two components of chromosomes—DNA and protein—became candidates for the genetic material • 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 Evidence That DNA Can Transform Bacteria • 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 • 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 , now defined as a change in genotype and phenotype due to assimilation of foreign DNA 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 EXPERIMENT RESULTS • 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 Evidence That Viral DNA Can Program Cells • 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 Phage head Tail sheath Tail fiber DNA Bacterial cell 100 nm • In 1952, Alfred Hershey and Martha Chase performed experiments showing that DNA is the genetic material of a phage known as T2 • To determine this, they designed an experiment showing that only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection • They concluded that the injected DNA of the phage provides the genetic information Figure 16.4-3 Bacterial cell Phage Batch 1: Radioactive sulfur ( 35 S) Radioactive protein DNA Batch 2: Radioactive phosphorus ( 32 P) Radioactive DNA Empty protein shell Phage DNA Centrifuge Centrifuge Radioactivity...
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This note was uploaded on 01/29/2012 for the course BSCI 105 taught by Professor Jensen during the Fall '07 term at Maryland.

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Lectures 27 & 28 Molecular Basis of Inheritance -...

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