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BIOLOGY 1A03 (168)
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Chapter 15

Textbook and Class Notes Collaborated - Unit 3 - Chapter 15 Bio 1A03

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McMaster University
Xudong Zhu

Bio 1A03 Unit Three: Gene Structure and Expression Chapter 15: How Genes Work Key Concepts  Most genes code for proteins  In cells, information flows from DNA to RNA to proteins  DNA is transcribed by RNA polymerase to messenger RNA, and then messenger RNA is translated by ribosomes to proteins  Each amino acid in a protein is specified by a group of three bases in RNA 15.1 What Do Genes Do?  Knock-out mutants/null mutants/loss-of-function mutants – alleles that do not function One-Gene and One-Enzyme Hypothesis (Beade and Tatum)  Genes contain the information needed to make proteins, many of which function as enzymes  Predicts that the knockout of genes would lead to loss of enzymes required for synthesizing a particular product such as arginine  Matagenesis – Application of high energy radiation to create a large number of N. crassa mutants  Genetic screens – a technique used for picking certain types of mutants out of many thousands of randomly generated mutants o Raised irradiated cells on a medium that included arginine, then they grew a sample of each type of cell on a medium that lacked arginine  If an individual could grow in the presence of arginine but failed to grow without arginine – it couldn’t make its own arginine; the offspring of these cells also had this defect – they were confident that they had isolated individuals with mutations in the genes for one or more of the enzymes o Grow these mutants in normal media that lack arginine but are supplemented with nothing, arginine, citrulline or ornithine 15.2 The Central Dogma of Molecular Biology  Francis Crick proposed that the sequence of bases in DNA is a kind of code and that DNA is an information storage molecule  Different combinations of bases could specify the 20 amino acids Bio 1A03  A particular stretch of DNA (a gene) contains the information to specify the amino acid sequence of one protein  The information encoded in the base sequence of DNA is not directly translate into the amino acid sequenced of proteins RNA as the Intermediary Between Genes and Proteins  Francois Jacob and Jacques Monod proposed that RNA molecules act as a link between genes and the protein-manufacturing centers  DNA is inside nucleus, ribosome (protein synthesis occurs) is in the cytoplasm  Messenger RNA (mRNA) – was found to carry information from DNA to the site of protein synthesis  RNA polymerase – synthesizes/polymerizes ribonucleotides into strands of RNA according to the information provided by DNA o Does not require a primer  Design of experiments to demonstrate how information is transferred from DNA to mRNA The Central Dogma  Summarizes the flow of information in cells: DNA codes for RNA, which codes for proteins: o DNA  RNA  Proteins  The sequence of bases in a particular stretch of DNA specifies the sequence of bases in an RNA molecule, which specifies the sequence of amino acids in a protein  DNA is transcribed to messenger RNA o Transcription – permanent record in DNA is copied to short-lived form RNA  The mRNA is then translated to proteins o Translation – transferring of informat
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