Regulation of gene expression
16
Regulation of gene expression References: 1.Stryer: “Biochemistry”, 5 th Ed. 2.Hames & Hooper: “Instant Notes in Biochemistry”, 2 nd Ed.
description
Regulation of gene expression. References: Stryer : “Biochemistry”, 5 th Ed. Hames & Hooper: “Instant Notes in Biochemistry”, 2 nd Ed. 1. Basic principles of gene control. What is gene expression? - PowerPoint PPT Presentation
Transcript of Regulation of gene expression
Regulation of gene expression
References: 1. Stryer: “Biochemistry”, 5th Ed.2. Hames & Hooper: “Instant Notes in
Biochemistry”, 2nd Ed.
1. Basic principles of gene control
What is gene expression?It is a process by which a gene's
information is converted into the structures and functions of a cell.
For a protein encoding gene, it is a process of the transcription of a gene into mRNA, and the latter is translated into protein.
How to control gene expression?
In prokaryotic cells, gene expression is regulated primarily at the level of transcription by metabolites;
In eukaryotes it is controlled by much more complex mechanisms, including the action of protein factors, hormones, etc.
Control of gene expression in prokaryotes
R Structural gene
SubstrateProduct
Enzyme
mRNA
DNA
R
Control of gene expression in eukaryotes
DNA
Protein
mRNARNA
synthesis
InactivemRNA
mRNA
InactiveProtein
Transcript.control
1
RNA processingcontrol
2
RNAtransportcontrol
3mRNA
degradationcontrol
5
Translationcontrol
4
Protein activitycontrol6
Nucleus
Cytosol
2. Regulation of Prokaryotic gene expression– the operon theory
Operons are groups of genes that function to produce proteins needed by the cell.
There are two types of genes in operonsA. Structural genes code for proteins
needed for the normal operation of the cell.
B. Regulator genes code for proteins that regulate other genes.
lac I lac Z lac A lac Y PlacI Plac Olac
Plac : promoter; Olac: operator; lac Z: b-galactosidase; lacY: permease; Lac A: transacetylase; lac I: structural gene for lac repressor; PlacI : promoter for lac I.
Lactose Operon
Regulation of the lac operon in E. coli.
p i p o z y aThe lact Operon
RepressormRNA
Repressor
The repressor binds to the operator region and prevents RNA polymerase from transcribing the structural genes
In the presence of lactose
p i p o z y aThe lact Operon
Lactose binds the repressor and allows RNA polymerase access to the operator, resulting in transcription of the structural gene
b-galactosidase permease transacetylase
RepressormRNA
Repressor
Lactose
mRNA
In the presence of glucose & lactose
p i p o z y aThe lact Operon
glucose
AdenylcyclasecAMP ATP
L actose
Low level of transcription
In the absence of glucose and presence of lactose
p i p o z y aThe lact Operon
L actose
High level of transcription
AdenylcyclasecAMP ATP
CAP
active
CAP: catabolite activator protein
Tryptophan OperonThe trp operon encodes the genes for the
synthesis of tryptophan
L A BP,O a CDE
Genes for enzymes
P: promoter, O: operator, a: attenuator, L: leader sequence, A,B,C,D,E: enzymes
of the Trp pathway
Regulation of the trp operon in E. coli.
Binding of Trp to the trp repressor increases the activity of the repressor, and therefore Trp is known as a co-repressor.
Expression of the trp operon is also regulated by attenuation. The attenuator region contains tandem Trp codons, which play a role to attenuate the transcription of the following genes.
Regulation of the trp operon
