Camerini 1

Camerini 1 - BioSci 99B Protein Synthesis Dr. David...

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BioSci 99B Protein Synthesis Dr. David Camerini dcamerin@uci.edu
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Lecture 1: The central dogma of molecular biology Today, we will discuss the following: -Information transfer in biological systems -Classical genetic vs. modern biochemical definitions of a gene -One gene, one enzyme hypothesis -Basic properties of the genetic code -Properties of proteins and amino acids -Colinearity between DNA and protein sequences -Biochemical basis of mutation
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The central dogma of molecular biology Dogma = An authoritative principle, belief, or statement of i deas or opinion, especially one considered to be absolutely true. Transcription Translation DNA ------------------> mRNA -----------------> protein phosphodiester bond phosphodiester bond peptide bond
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Biological “information flow” Genes contain information coded in the linear sequence of DNA that is transcribed into RNA which is then used to direct the synthesis of proteins, which are linear sequences of amino acids. Why have an intermediate (e.g. mRNA)? 1. To facilitate additional levels of regulation (e.g. transcriptional, post- transcriptional, translational, post- translational). 2. Reduces the necessity to amplify sequences of DNA for maximal “expression” of a particular protein. 3. Separation of DNA replication from protein synthesis. 4. Spatial separation of replication and transcription (nucleus) from translation (cytoplasm) in eukaryotes.
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Classical vs. modern definition of a gene The purpose of today’s lecture is to present to you how we made the connection between genes and proteins. It was through genetic analysis of mutants that we made a connection between DNA and proteins and the fundamental properties of gene structure and information encoding were revealed. Sixty years ago, the geneticist’s definition of a gene was very different from the one we have now. In fact, some geneticists believed that genes could not be explained in terms of a biochemical structure. A. Classical genetic definition. Genes are discrete, heritable elements that control an observable phenotype or biological property (e.g. Mendel). B. Modern Biochemical definition. Genes are pieces of DNA that direct the synthesis of proteins or RNA.
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“One Gene, One Enzyme”: Beadle and Tatum: 1st observation that genes encode enzymes, not just observable traits. Used Neurospora crassa (bread mold). “Wildtype cells could grow on simple medium, but mutants (produced with x-rays) could not; had to supplement medium with nutrients. How did they use this system to refine our definition of a gene? Replica plating technique…
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Complementation Beadle and Tatum used “complementation” tests to demonstrate that more than one gene might be involved in producing an observable trait. They produced mutants of
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Camerini 1 - BioSci 99B Protein Synthesis Dr. David...

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