Download Genes and How They Work

Genes and How They Work
Computer Filename: genes2.ppt
 Hugh B. Fackrell
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Overview
Genes composed of DNA within the
chromosome
 Genes code for proteins
 DNA is transcribed into RNA
 RNA is translated into Protein by
ribosomes
 Genes regulated by control of RNA
production
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CODONS
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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
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RNA: AUG
 DNA: TAC
 also codes for methionine
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Stop Codon
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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 polypeptide
 Start & Stop Signals: Where to read
the blueprint
 Regulatory Sequences: When to read
the blueprint: operators, enhancers,
promotors
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Interpreting the Genetic Code
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Two step process :
–Transcription DNA --> RNA
–Translation RNA--> protein
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Operon
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A cluster of functionally related genes
and regulator sites
 transcribed onto single mRNA
 common in prokaryotes and fungi
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Transcription
Production of an RNA copy of the gene
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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
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Transcription Regulation
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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
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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
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Negative control :Blocks transcription of
DNA to mRNA
 Postive control: Initiates transcription of
DNA to mRNA
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Negative Control
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Process is called Repression
 Process is controlled by a protein called a
Repressor
 Repressor protein has two configurations
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Operator site
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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
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process called activation
 process controlled by a protein called
Activator
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CAP Protein
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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
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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
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