how and why genes are regulated

Four of the many different types of human cells:

They all share the same genome.What makes them different?

How and Why Genes Are Regulated

Gene ExpressionGenes are expressed as traits

Traits are proteins or result from reactions which are regulated by proteins, such as enzymes.

Genes are expressed through protein synthesis.

How Does A Cell Know? Which Gene To Express

& Which Gene Should Stay

Silent?

Gene Regulation

Patterns of Gene Expression in Differentiated Cells◦In cellular differentiation:

Certain genes are turned on and off. Cells become specialized in structure and function.

◦In gene expression: A gene is turned on and transcribed into RNA. Information flows from genes to proteins, genotype to

phenotype.◦ The regulation of gene expression plays a central role in

development from a zygote to a multi-cellular organism.

When a Gene is Expressed:◦It is active and is Transcribed into mRNA

When a Gene is Silent:◦It is in active and is Not Transcribed

Gene Regulation

Patterns of Gene Expression in Specialized Human Cells

Vocabulary RNA polymerase: RNA polymerase (RNAP or RNApol) is an enzyme that produces RNA.

Repressor: inhibits transcription of structural genes by binding to the operator

Regulatory gene: codes for the repressor

Promoter: area on the DNA to which the RNA polymerase attaches to begin transcription

VocabularyOperator: area of the DNA to which the repressor binds; “on/off” switch

Structural genes: code for enzymes which leads to a product

Expression Regulated By1. Promoters RNA Polymerase Binding Sites Certain DNA Base Pair Sequences

2. Start & Stop Base Pair Sequences

3. Regulatory Sites DNA Binding Proteins Regulate Transcription

Gene Regulation

Gene Regulation

What is an Operon? Group of Genes That Operate Together

For Example:◦E. coli ferments (digests) lactose To Do That It Needs Three Enzymes (Proteins), It Makes Them All At Once! 3 Genes Turned On & Off Together. This is

known as the lac Operon (lactose Operon)

Prokaryote Gene Regulation:

OperonsOperon: made of three parts1. Operator2. Promoter3. Group of genes

located together which express proteins for a similar function.

1. Inducible◦ Example: lac operon Lac = lactose

◦ Normally off but can be activated

2. Repressible◦ Example: trp operon Trp = tryptophan

◦ Normally on but can be inhibited

Two type of operons

The lac Operon◦ Regulates Lactose Metabolism◦ It Turns On Only When Lactose Is

Present & Glucose is Absent.Lactose is a Disaccharide

◦ A Combination of Galactose & Glucose To Ferment Lactose E. coli Must:

1. Transport Lactose Across Cell Membrane2. Separate The Two Sugars

Gene Regulation: lac Operon

Each Task Requires A Specific Proteinbut

Proteins Not Needed If Glucose Present (why waste energy if you already have

food?)so

Genes Coding For Proteins Expressed Only When There Is No Glucose Present

But Lactose Is Present

Gene Regulation: lac Operon

Gene Regulation: lac Operon

Gene Regulation: lac Operon

= Lactose

ADD LACTOSE

Gene Regulation: lac Operon

Key Concept:The lac Genes Are:

Turned Off By Repressors And

Turned On By The Presence Of Lactose

Gene Regulation: lac Operon

Operon Has 2 Regulatory Regions1. Promoter

(RNA Polymerase Binding)

2. Operator (O region) Bound To A lac Repressor

lac Gene Expression

lac Repressor◦ When Bound To O

Region : Prevents Binding of RNA Polymerase To Promoter

◦ Turns The Operon “OFF”

lac Gene Expression

lac Repressor Also Binds To Lactose◦ Higher Affinity For

Lactose When Lactose

Present lac Repressor Is Released From O Region◦ Allows Transcription of

All Three Genes

lac Gene Expression

Compare and Contrast

1. Based On Repressors2. Based On Enhancers3. Regulated At Protein

Synthesis

Regulation Can Be:

Operons UsuallyNOT Found In Eukaryotes

Key Concept:Most Eukaryotic Genes Are Controlled Individually And Have Regulatory Sequences That Are Much More Complex Than Prokaryotic Gene Regulation

Eukaryotic Gene Regulation

Eukaryotic Gene Regulation

TATA Box◦About 30 Base Pairs Long◦Found Before Most Genes◦Positions RNA Polymerase◦Usually TATATA or TATAAA◦Promoters Usually Occur Just Before The TATA Box

Eukaryotic Gene Regulation

Enhancer Sequences◦ Series of Short DNA Sequences◦ Many Types

Enormous Number Of Proteins Can Bind To Enhancer Sequences

◦ Makes Eukaryote Enhancement Very Complex

Eukaryotic Promoters

Some Enhance Transcription By Opening Up Packed Chromatin

Others Attract RNA Polymerase Some Block Access To Genes Key To Cell Specialization

◦ All Cells Have Same Chromosomes◦ Some Liver, Skin, Muscle, etc.

Eukaryotic Promotors

The End