Gene Regulation: The control of protein production

Prokaryotes Eukaryotes

A. Small circular genome

B. Unicellular (DNA instructions for only one cell type)

C. Most DNA codes for protein

D. Most of the genome is expressed

E. Mechanism: The Operon

I. Differences between gene regulation of prokaryotes and eukaryotes

A. Large genome, many strands, genes randomly distributed among the strands

B. Multicellular (DNA instructions for every cell type of the organism)

C. Most DNA as “junk DNA” (Repetitive DNA that make introns, centromeres, telomeres)

D. Little of the genome is expressed (20% max)

E. Mechanisms:

1. Chromosome Structure

2. Transcriptional Control

3. Post-Transcriptional Control

4. Translational Control

5. Post-Translational Control

Chapter 18 pages 360 -389

II. The Operon System Parts of the Operon

A. Structural Genes: The sequence of genes required to produce the desired product. Many are part of the same metabolic pathway and are in a specific order.

B. Promoter: Area of the DNA that allow attachment to the of RNA polymerase

D. Regulatory gene: Produces a protein that interacts with the operator

C. Operator: Part of the DNA that when bound to a specific protein will prevent the attachment of RNA polymerase

E. Types

1) Inducible operons example: Lac operon

2) Repressible operons example: Tryp operon

The Lac Operon: Controls the production of enzymes required to metabolize lactose

Lac operon turned off

PromoterRegulatory

gene

mRNA

Repressor Protein (active)

RNA polymerase

Structural genes

Operator

1. Active repressor binds to the operator

Lac operon turned on

Lactose

Inactive repressor

RNA polymerase

mRNA

Operator

Regulatory gene

Repressor Protein

Lac Z Lac Y Lac A

Galactosidase

Permease

Transacetylase

1. Lactose binds to active repressor and deactivates the repressor

2. RNA polymerase bonds to promoter allowing the transcription of the structural genes

Slide 2Why is it called an “inducible operon”?

2. RNA polymerase can not transcribe structural genes

(no lactose present) (lactose present)

Video

Promoter

Structural genes

The Tryp Operon: Controls the enzymes required to build tryptophan (amino acid) Operon turned off Operon turned on

Regulator geneOperator

Structural genes

mRNAmRNA mRNA

Tryptophan

Inactive repressor

Active Repressor

1. Inactive repressor is made active in the presence of tryptophan

Active Repressor

RNA Polymerase

RNA Polymerase

Inactive repressor Enzymes required for the

synthesis Tryptophan

Tryp ATryp BTryp CTryp DTryp E

1. Inactive repressor can not bond to the operator

Slide 2

Regulator geneOperator

2. Tryptophan is not synthesized since RNA polymerase cannot bond to promoter

2. RNA polymerase bonds to DNA so the enzymes for the synthesis of tryptophan are transcribed

Why is this called a “repressible operon”?

(Tryptophan present) (Tryptophan absent)Promoter Promoter

Areas of Control in Eukaryotic CellsControl Type Function / ExamplesMethodsChromosome Structure

1. Histone Acetylation

2. DNA Methylation

1. Spreads out nucleosomes to facilitate transcription

2. Makes genes inaccessible (Barr Bodies and Imprinting)

19-01-DNAPacking.mov

Transcriptional Control

1. Transcription factors bond at promoter site to increase RNA polymerase affinity

2. Activator proteins bind to DNA Enhancers to bend DNA to form transcription initiation complex

1. Hormones & Signal Transduction

2. Formation of transcription complex

Albumin (liver) vs. Crystalin (lens)

19-09-TurningOnAGene.mov

Post Transcriptional

Control

Translational Control

Post Translational

Control

1. mRNA processing introns and exons

2. mRNA export

3. Long lived or short lived mRNA

1. Intron and exon splicing will modify the protein produced

2. 5’ Cap and Poly A tail can prevent export to cytoplasm

3. RBC have long lived mRNA

19-08-RNAprocessing.mov

19-10-ControlOfTranslation.mov

19-12-ProteinProcessing.mov

1. Translation Repressor Protein binds to 5’ Cap preventing translation

2. Non-Coding RNAs

a. MicroRNA (miRNA)

b. Small Interfering RNA (siRNA)

1. mRNA prevented from translation in egg until after fertilization

2. Non-coding RNA that binds with protein that degrades or prevents the translation of coding RNA

1. Protein Processing modifies the activity of proteins

2. Selective degradation

1. Insulin and Digestive Enzymes

2. Targeting by

a) ubiquitin

b) Proteasomes

Steroid Hormone Gene Activation Protein Hormone Gene Activation

Hormones and Transcription Factors

11-17-SignalTransduction.mov

Slide 5

Slide 1

Levels of DNA Packaging

Slide 5

Slide 5

How Introns and Exons Control Gene Expression

Proteasomes in the cytosol

Protein Modification: Proteasomes

Slide 5

Organization of Prokaryote Genes

Slide 3

Slide 4

Slide 2

Gene Regulation

Slide 1

Androgens are illegal because they work!!Slide 6

How Activators and Enhancers Influence Transcription

Slide 5

(Proteins made by cell)

(DNA Codes)

How 2 Different Cells with Identical DNA can Produce Different Proteins

(Blood Protein)

(Eye Lens Protein )

Slide 5

Slide 5

The Effect of Histone Acetylation

Origin and Function of MiRNA

Coded mRNACoded mRNA

Slide 5