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Download DNA – the heredity material DNA - genetic material Discovering
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DNA – the heredity material Very early it was discovered chromosomes are composed of proteins and DNA. But it took several experiments to conclusively determine specifically which substance made up genes. Griffith Experiment Documented movement of genes from one organism to another (transformation 1928). – Avery Experiment (1944) Removed almost all protein from bacteria, and found no reduction in transforming activity. – Hershey-Chase (1952) U se d radioactive isotopes to label DNA and protein. Found genes used to specify new generations of viruses were made of DNA. DNA - genetic material Eukaryotes – DNA located in the nucleus membrane bound organelle Prokaryotes – DNA located in the nucleoid. No membrane surrounded organelle Discovering DNA Structure DNA made up of nucleotides. – Central sugar, phosphate group, and an organic base. Purines - Large bases – Adenine and Guanine Pyrimidines - Small bases – Cytosine and Thymine Nucleotide Base DNA – 4 nucleotide bases 4 base nucleotides Chargaff’s Rule A =T and G=C Discovering DNA Structure Watson and Crick 1953 &( Wilkins) deduced structure of DNA as a double helix. Base pairs linked Double Helix structure two stands of nucleotides Outer part of the ladder is the sugar-phosphate backbone Anti-parallel allows for H-bonds between complementary base pairs H- bonds between base pairs 3 H-bonds Packaging DNA in the nucleus DNA Replication Weak hydrogen bonds between base pairs hold DNA strands together. Each chain in the helix is a complimentary mirror image of the other. – Double helix unzips and undergoes semi-conservative replication. Confirmed by Meselson-Stahl Experiment. Bi-directional replication Proofreading by DNA polymerase III Genes to Proteins Producing proteins from genes is known as gene expression – DNA - Gene RNA - Protein Expression - Use of information in DNA to direct production of particular proteins. – Transcription - mRNA molecule is synthesized from gene within DNA. – Translation - mRNA used to direct protein production. DNA vs RNA Transcription The RNA copy of a gene used to produce a protein is called messenger RNA (mRNA). Is all of the DNA expressed? Codons – triplet code Translation – mRNA >> polypeptide Translation – the ribosome Translation – the ribosome Overview of translation