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Genes and How They Work

Computer Filename: genes2.pptHugh B. Fackrell

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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

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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

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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

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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

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Gene Regulation (1/6)

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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)

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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