Replication

Replication - BILD 1 Lecture 15 5-20-2008 DNA Replication...

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Unformatted text preview: BILD 1 Lecture 15 5-20-2008 DNA Replication Preview Heredity experiments Griffith (1928) Avery, MacLeod, McCarty (1944) Hershey and Chase (1952) Watson, Crick, and Franklin (1953) Meselson and Stahl (1958) DNA replication Proofreading Telomere Central dogma of biology Transcription Translation Replication DNA RNA Protein Requirements of Genetic Material Must encode heritable information in some logical way Must be precisely copied Must be capable of occasional change Possibilities: DNA, RNA, proteins The Search for the Genetic Material The role of DNA in heredity Was first worked out by studying bacteria and the viruses that infect them Frederick Griffith (1928) Mixed heat-killed pathogenic Streptococcus pneumoniae strain (S) with living nonpathogenic strain (R). Living S cells Living R cells Heat-killed S cells Mixed heat-killed S and living R cells Mouse dies Mouse healthy Mouse healthy Mouse dies Living S cells are found in blood sample. The Search for the Genetic Material: Evidence that DNA can transform bacteria Some living R cells became pathogenic (like S cells)! Griffith called the phenomenon transformation (Now defined as a change in genotype and phenotype due to the assimilation of external DNA by a cell) Thus, something is transferred and causing the changes. Avery, MacLeod and McCarty (1944) Purified DNA as the pathogenic molecule from killed bacteria However, others were still skeptical. Proteins seemed to be a cooler genetic material. Transformation The Search for the Genetic Material: Evidence That Viral DNA Can Program Cells Additional evidence for DNA as the genetic material came from studies of a virus that infects bacteria Bacteriophages are viruses that infect bacterial cells Phage head Tail Tail fiber DNA Bacterial cell 100 nm Radioactivity (phage protein ) in liquid Phage Bacterial cell DNA Centrifuge Pellet (bacterial cells and contents) Radioactivity (phage DNA ) in pellet Alfred Hershey and Martha Chase (1952) Showed that DNA is the genetic material of phage T2 The Search for the Genetic Material: The Hershey-Chase Experiment Radioactive- labeled protein Radioactive- labeled DNA 1 2 Sugar-phosphate backbone Nitrogenous bases 5 end O O P O CH 2 5 4 O H H O H H H 3 1 H O CH 3 N O N H Thymine (T) O O P O O CH 2 H H O H H H H N N N H N H H Adenine (A) O O P O O CH 2 H H O H H H H H H H N N N O Cytosine (C) O O P O CH 2 5 4 O H O H H 3 1 OH 2 H N N N H O N N H H H H Sugar (deoxyribose)...
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This note was uploaded on 09/27/2008 for the course BILD 1 taught by Professor Boulanger during the Spring '08 term at UCSD.

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Replication - BILD 1 Lecture 15 5-20-2008 DNA Replication...

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