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04/20/231
Genes and How They Work
Computer Filename: genes2.pptHugh B. Fackrell
04/20/232
Overview
Genes composed of DNA within the chromosome
Genes code for proteinsDNA is transcribed into RNARNA is translated into Protein by
ribosomesGenes regulated by control of RNA
production
04/20/233
CODONS
sequences of three adjacent nucleotides that code for one amino acid or polypeptide termination
64 codons encrypt of ~ 20 amino acids degenerate RNA: ACU, ACC,ACA, ACG
threonine degenerate DNA: TGA, TGG,TGT, TGC
threonine
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Start Codon
RNA: AUG
DNA: TAC also codes for methionine
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Stop Codon
Nonsense Codons RNA: UAA,UAG,UGA DNA: ATT, ATC, ACT
04/20/236
Structure of the Genetic Code
DNA : sequences of four nucleotides A,T,G,C
CODONS : blueprint for the polypeptideStart & Stop Signals: Where to read
the blueprintRegulatory Sequences: When to read
the blueprint: operators, enhancers, promotors
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Interpreting the Genetic Code
Two step process :
–Transcription DNA --> RNA
–Translation RNA--> protein
04/20/238
Operon
A cluster of functionally related genes and regulator sites
transcribed onto single mRNA common in prokaryotes and fungi
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Transcription
occurs in nucleus DNA unravels- single strand RNA Polymerase binds to Promotor site Reads from start sequence(ATG) assembles complementary single strand of RNA
(primary RNA) Disengages when reaches stop codon
Production of an RNA copy of the geneProduction of an RNA copy of the gene
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Transcription Regulation
Controlled by DNA Binding proteins that bind to specific nucleotide sequences
some bind in the groove of DNA helix some bind to single stranded DNA Promotor site Activator site (positive regulation) Operator site (negative regulation) Enhancer site
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Promotor Site
Controls when DNA transcribed Called TATA box Sequence TTGACA or TATAAT (‘sense’) complementary sequences are AACTGT
and ATATTA(‘antisense’) Start codon 30 BP downstream
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DNA Binding Proteins
Negative control :Blocks transcription of DNA to mRNA
Postive control: Initiates transcription of DNA to mRNA
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Negative Control
Process is called Repression Process is controlled by a protein called a
Repressor Repressor protein has two configurations
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Operator site
sequence of nucleotides between the promotor and the gene
binding site for the repressor protein blocks RNA polymerase from reading the
gene
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Tryptophan Repressor: Gene off
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Tryptophan repressor : gene ON
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Positive Control
process called activation process controlled by a protein called
Activator
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CAP Protein
Positive regulator Binds to Outside of DNA Alternative to glucose metabolism Glucose decrease increases CAMP CAMP binds to CAP CAP binds to DNA
04/20/2319
Gene Regulation (1/6)
04/20/2320
Gene Regulation (2/6)
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Gene Regulation (3/6)
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Gene Regulation (4/6)
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Gene Regulation (5/6)
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Gene Regulation (6/6)
04/20/2325
Question
Design a gene regulation system that has an activator that is turned OFF in the presence of a substrate and a promotor that is turned ON in the presence of a product.
Define a series of gene regulators that would turn a ‘cascade’ on and then off in series
Define, promotor, activator and operator repressor, enhancer