Download Transcriptional Control

Gene Regulation: The control of protein production
Chapter 18 pages 360 -389
I. Differences between gene regulation of prokaryotes and eukaryotes
Prokaryotes
A. Small circular genome
B. Unicellular
Eukaryotes
A. Large genome, many strands, genes
randomly distributed among the strands
B. Multicellular
(DNA instructions for every cell type of the organism)
(DNA instructions for only one cell type)
C. Most DNA as “junk DNA”
C. Most DNA codes for protein
(Repetitive DNA that make introns, centromeres, telomeres)
D. Most of the genome is expressed
D. Little of the genome is expressed (20% max)
E. Mechanism: The Operon
E. Mechanisms:
1. Chromosome Structure
2. Transcriptional Control
3. Post-Transcriptional Control
4. Translational Control
5. Post-Translational Control
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
C. Operator:
Part of the DNA that when bound to a specific protein will
prevent the attachment of RNA polymerase
D. Regulatory gene: Produces a protein that interacts with the operator
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 on
Lac operon turned off
Structural
Promoter
genes
Regulatory
Promoter
gene
Operator
Operator
(lactose present)
(no lactose present)
Regulatory
gene
Structural genes
Lac Z
Lac Y
Lac A
RNA polymerase
RNA
polymerase
mRNA
mRNA
Galactosidase
Repressor Protein
(active)
Repressor
Protein
Transacetylase
Permease
Lactose
Inactive
repressor
1. Active repressor binds to the
operator
1. Lactose binds to active repressor and
deactivates the repressor
2. RNA polymerase can not
transcribe structural genes
2. RNA polymerase bonds to promoter
allowing the transcription of the structural
genes
Why is it called an “inducible operon”?
Video
Slide 2
The Tryp Operon: Controls the enzymes required to build tryptophan (amino acid)
Operon turned off
Operon turned on
(Tryptophan present)
Promoter
Structural
genes
Regulator gene
(Tryptophan absent)
Promoter
Regulator gene
Operator
Operator
RNA
Polymerase
RNA
Polymerase
mRNA
Active
Repressor
Tryp E Tryp D Tryp C Tryp B
mRNA
Tryp A
mRNA
Inactive
repressor
Active
Repressor
Inactive
repressor
Enzymes required for the
synthesis Tryptophan
Tryptophan
1. Inactive repressor is made active in the
presence of tryptophan
2. Tryptophan is not synthesized since
RNA polymerase cannot bond to promoter
1. Inactive repressor can not bond to
the operator
2. RNA polymerase bonds to DNA so
the enzymes for the synthesis of
tryptophan are transcribed
Why is this called a “repressible operon”?
Slide 2
Areas of Control in Eukaryotic Cells
Control Type
Methods
1. Histone Acetylation
Chromosome
Structure
2. DNA Methylation
Transcriptional
Control
Post
Transcriptional
Control
Translational
Control
1. Spreads out nucleosomes to facilitate
transcription
2. Makes genes inaccessible (Barr Bodies
and Imprinting)
1. Transcription factors bond
at promoter site to
increase RNA polymerase
affinity
1. Hormones & Signal Transduction
2. Activator proteins bind to
DNA Enhancers to bend
DNA to form transcription
initiation complex
2. Formation of transcription complex
1. mRNA processing
introns and exons
Albumin (liver) vs. Crystalin (lens)
1. Intron and exon splicing will modify
the protein produced
2. mRNA export
2. 5’ Cap and Poly A tail can prevent
export to cytoplasm
3. Long lived or short
lived mRNA
3. RBC have long lived mRNA
1. Translation Repressor
Protein binds to 5’ Cap
preventing translation
2. Non-Coding RNAs
a. MicroRNA (miRNA)
Post
Translational
Control
Function / Examples
b. Small Interfering RNA
(siRNA)
1. Protein Processing modifies
the activity of proteins
2. Selective degradation
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. Insulin and Digestive Enzymes
2. Targeting by
a) ubiquitin
b) Proteasomes
Hormones and Transcription Factors
Steroid Hormone Gene Activation
Protein Hormone Gene Activation
Slide 5
Slide 1
Levels of DNA Packaging
Slide 5
How Introns and Exons Control Gene Expression
Slide 5
Protein Modification: Proteasomes
Proteasomes
in the cytosol
Slide 5
Organization of Prokaryote Genes
Slide 3
Slide 4
Slide 2
Slide 1
Androgens are illegal because they work!!
Slide 6
How Activators and Enhancers Influence Transcription
(Proteins made by cell)
(DNA Codes)
Slide 5
How 2 Different Cells with Identical DNA can Produce Different Proteins
(Blood Protein)
(Eye Lens Protein )
Slide 5
The Effect of Histone Acetylation
Slide 5
Origin and Function of MiRNA
Coded mRNA
Coded mRNA
Slide 5