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Gene Expression
Remember, every cell in your body contains the exact same DNA…
…so why does a muscle cell have different structure and function than a nerve cell?
Review: DNA codes for…
Proteins being produced can be turned off and on just like a light switch based on the needs of a cell.
Chromosomes
Gene 1
Gene 2
Gene 3
Gene 4
Gene 5
Gene 6
A structurally organized single piece of coiled DNA containing many different genes. Each gene will code for ONE single PROTEIN.
Regulated Gene Expression
Regulated = control the speed/amount
Gene Expression = using the information from a gene to express a protein
Regulated Gene Expression = how a cell controls the speed or amount of a gene being expressed as a protein
Methods of regulation
In Eukaryotes:1.Regulating transcription (DNA mRNA) by:1. Activator
Proteins2. Promoters
2. Splicing of mRNAExons - Expressed
In Prokaryotes:
1.Regulating transcription (DNA mRNA) by:1. Operators2. Promoters3. Repressor
Protein
Regulation in Eukaryotes#1 Regulating Transcription (DNA mRNA)
If a protein is needed by the cell, a gene coding for that protein needs to be expressed, TRANSCRIPTION WILL OCCUR.
If a protein is NOT needed by the cell, TRANSCRIPTION WILL STOP.
Eukaryotic Transcription Factors
- Activator Protein - a molecule that turns ON transcription
- Transcription Factors – molecules that allow RNA Polymerase to bind to DNA and begin transcription
- Promoter – sequenceon DNA before the Gene where ActivatorProteins and TranscriptionFactors can bind to…
Eukaryotic:Transcription will TURN ON
When Activators and Transcription Factors are both bound to the Promoter site, RNA polymerase will bind to DNA and begin transcription.
The gene will be transcribed and the protein will be translated/expressed.
Eukaryotic: Splicing RNAAfter Transcription: Portions of the transcribed mRNA is (spliced) cut outExons – the portions of the gene on mRNA that are cut, translated, and EXPRESS proteinsIntron – the portions of the gene on mRNA that do not code for proteins and are NOT expressedThe spliced Exons will then code for a Protein!
Regulation of Prokaryotic Genes
Operon – multiple genes that are grouped together on one consecutive segment of DNA that is transcribed/copied onto ONE single mRNA
Promoter – sequence in an operon where RNA polymerase binds to and begins transcription
Operator – sequence in an operon where a repressor can bind or unbind to
Repressor – a protein that can bind to the operator to PREVENT Transcription from occurring
Lac Operon - ProkaryotesLac Operon: a DNA sequence of three genes (Lac Z, Lac Y, & Lac A) that codes for proteins that break down lactose
When lactose is present…
- Repressor is NOT BOUND to the operator
- RNA polymerase can bind to the PROMOTER and TRANSCRIPTION OCCURS
- Expression of lactase proteins occurs
When lactose is absent…
Repressor IS BOUND to the operator
RNA polymerase can NOT bind to the PROMOTER and TRANSCRIPTION Does NOT Occur
Expression of lactase proteins is REPRESSED! (switch is OFF)