of gene expression References Stryer Biochemistry 5 th Ed Hames amp Hooper Instant Notes in Biochemistry 2 nd Ed 1 Basic principles of gene control What is gene expression ID: 316432
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Slide1
Regulation of gene expression
References:
Stryer
: “Biochemistry”, 5
th
Ed.
Hames
& Hooper: “Instant Notes in Biochemistry”, 2
nd
Ed.Slide2
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. Slide3
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.Slide4
Control of gene expression in prokaryotes
R
Structural gene
Substrate
Product
Enzyme
mRNA
DNA
RSlide5
Control of gene expression in eukaryotesSlide6
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 operons
Structural genes code for proteins needed for the normal operation of the cell.
Regulator genes code for proteins that regulate other genes.Slide7
P
lac
:
promoter;
O
lac
:
operator;
lac Z:
b
-galactosidase;
lacY:
permease; Lac A:
transacetylase; lac I: structural gene for lac repressor; PlacI : promoter for lac I.Lactose OperonSlide8
Regulation of the lac operon in
E. coli.
Repressor
mRNA
Repressor
The repressor binds to the operator region and prevents RNA polymerase from transcribing the structural genesSlide9
In the presence of lactose
mRNASlide10
In the presence of glucose & lactose
Low level of transcriptionSlide11
In the absence of glucose and presence of lactose
active
CAP: catabolite activator proteinSlide12Slide13
Tryptophan Operon
The trp operon encodes the genes for the synthesis of tryptophanSlide14
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. Slide15Slide16