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)