LS8Transcription

LS8Transcription - Transcription l Overview q q q l...

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Transcription  Transcription  Overview Template - DNA Enzyme -  RNA polymerase Steps of transcription Prokaryotic transcription Eukaryotic transcription
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1. "Central Dogma" Central dogma, originally proposed by Francis Crick, states that the flow of the genetic information in a cell is always from DNA to RNA to protein. Although the principle of central dogma is generally correct, exceptions have been found later. e.g. retroviruses like HIV make DNA from RNA. DNA RNA Protein replication transcription translation
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2. Gene structure - A gene is the entire DNA sequences required to encode a functional polypeptide or RNA (tRNA, rRNA, miRNA etc). - Cistron is an old name for gene. -A pseudogene is DNA sequence that looks like a gene but is not transcribed, pseudogenes are most likely dead genes.
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Number of genes correlates generally Number of genes correlates generally with level of complexity of organism with level of complexity of organism Bacteria Bacteria 2,000-6,000 2,000-6,000 Yeast Yeast 6,000 6,000 Fruit fly Fruit fly ~14,000 ~14,000 Mammals Mammals ~30,000 ~30,000 Organism Organism Genes Genes
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1. Prokaryotic genes are polycistronic —one promoter direct the synthesis of a mRNA that can encode more than one proteins 2. Eukaryotic genes are monocistronic —one promoter direct the synthesis of a mRNA that encodes only one protein . Procaryotic and eukaryotic genes Eukaryotes prefer to do things in more sophisticated ways to achieve more control of the process, so every gene could have its own expression profile. Proteins encoded by a prokaryotic polycistronic gene are usually all involved in the same biochemical pathway. This allows simple regulation of the whole pathway desired for fast growing bacterial cells.
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Example: five enzymes are need to synthesize tryptophan in both prokaryotes and eukaryotes One polycistronic gene in E. coli, transcribed into one mRNA, and translated into 5 proteins Five monocistronic genes in yeast, transcribed into 5 mRNA, and translated into 5 proteins
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3. Transcription A gene is expressed in two major steps: transcription for RNA synthesis, and t ranslation for protein synthesis
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Transcription = RNA synthesis -All cellular RNAs are synthesized by the transcription process. -Transcription is a DNA-dependent RNA polymerization reaction
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LS8Transcription - Transcription l Overview q q q l...

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