Ch17-20 transcription - What we will cover 1 How was one...

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What we will cover: 1. How was one gene associated with one polypeptide 2. How DNA code is turned into protein sequence 3. The genetic code 4. How DNA is transcribed
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1. How was one gene associated with one polypeptide
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Flow of genetic information -sequence of DNA nucleotides determines traits of organism -nucleotide sequence lead to specific proteins -link between inherited DNA and traits of the organism -proteins are link between genotype and phenotype - gene expression - occurs in two steps 1. transcription- production of RNA 2. translation- polypeptide synthesis
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Discovery of gene to protein relationship -Archibald Garrod- British physician 1909- first to suggest genes dictate phenotype through enzymes -inherited disease affects ability to make a specific enzyme -result in inborn errors in metabolism -example- alkaptonuria- urine turns black- darken on exposure to air -do not have enzyme that metabolizes alkapton
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-enzymes control synthesis and degradation of metabolic products -loss of specific enzyme results in block of pathway or loss -ex. eye color in fruit flies- metabolic pathway leads to color -loss of enzymes along the process- block in color or altered color
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Further evidence for gene enzyme relationship -mutation of bread mold - Neurosproa crassa -use X-rays to create mutations -normally grow on minimal media -synthesize all needed compounds -mutants generated that no longer grow on minimal media -need complete growth media - media with all 20 amino acids
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-mutant mold develop deficiences in specific metabolic pathways -grow on minimal media plus one amino acid -unable to synthesize one amino acid
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Metabolic pathways can be further broken down -mutants within single amino acid pathway are in three classes -represent mutations in specific steps
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-lead to strong support for one gene- one enzyme hypothesis -use of biochemistry and genetics to work out metabolic steps -further work to identify defective enzymes lends additional support to hypothesis
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What does a gene encode -not all proteins are enzymes -many proteins are structural -revise to one gene- one protein -not all genes encode for entire protein -many proteins consist of multiple polypeptides-ex. hemoglobin -multiple genes encode polypeptide -revise to one gene- one polypeptide
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2. How DNA code is turned into protein sequence
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Flow of information- DNA to proteins
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