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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
How 2 Different Cells with Identical DNA can Produce Different Proteins
(Blood Protein)
(Eye Lens Protein )
Slide 5
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