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Gene expression in prokaryotes
Genetic expression is the process by which inheritable information from a gene, such as the DNA sequence, is made into a functional gene product, such as protein or RNA
Non-protein coding genes (e.g. rRNA genes, tRNA genes) are transcribed, but not translated into protein
Group of organisms lacking a cell nucleus or any other membrane-bound organelles.
Differ from the eukaryotes, which have a cell nucleus
Mode of division is binary fission Prokaryotes exhibit efficient genetic
mechanisms to respond to environmental conditions
Rod-Shaped Bacterium, Escherichia coli dividing by binary fission
Rod-Shaped Bacterium,
hemorrhagic E. coli, strain
* * * * *
Type B
Inducible gene− Regulated by inducer/activator
Constitutive gene− Not subjected to regulation
Control at the level of transcription Induction - the production of a
specific enzyme/s in response to the presence of a substrate
Repression - the cessation of production of a specific enzyme/s in response to an increased level of a substrate
All of the genes which encode the enzymes necessary for the pathway are found next to each other on the E. coli chromosome
A single mRNA carries information for multiple proteins
This type of mRNA is called a polycistronic mRNA and is totally unique to prokaryotes
An operon model is a self-regulating series of genes found on DNA that work in concert
It includes a special segment of genes that are regulators of the protein synthesis, but do not code for protein, called the promoter and operator regions
Lactose (Lac), Tryptophan (Trp), L-Arabinose (Ara)
Inducible system
Three genes part of an operon that code for three separate enzymes
Needed for the breakdown of lactose, a simple sugar
Lac IPromot
er gene
Operator
geneLac Z Lac Y Lac A
RNA polymerase
Repressortetramer
R
Translation & Transcription
Inactive repressor
Desired product
Lac IPromot
er gene
Operator
geneLac Z Lac Y Lac A
R
Translation & Transcription
RNA polymerase
No Gene
Expression
Lac IPromot
er gene
Operator
geneLac Z Lac Y Lac A
mRNA
R R
RR
Lactose absentRepressormolecules
Repressortetramer
No Gene
Expression
RNA polymerase
Lac IPromot
er gene
Operator
geneLac Z Lac Y Lac A
mRNA
R R
RR
RNA polymerase
mRNA
Thiogalactoside
transacetylase
Permease
-galactosid
ase Inducer
Inactive repressor
R
Lactose/ Isopropyl
Thiogalactoside (IPTG) present
If there occurs no glucose metabolism
Lac I Promoter gene
Operator gene Lac Z Lac Y Lac A
cAMP
Glucose pool gets depleted due to metabolism
CAP-cAMP complex formed
cAMP
RNA polymerase
mRNA
-galactosidase
Permease
Thiogalactoside transacetylase
If there occurs glucose metabolism
R
IR
I
Trp Operon ModelTrp A
Trp C
Trp B
Trp LP/O Trp
ETrp D
Tryptophan
synthetase (B
protein)
Tryptophan
synthetase (A
protein)
Anthranilate
synthetase
Anthranilate
synthetase
Glycerol-phosphat
e syntheta
se
1. L-arabinose operon model
2. Controlled by a dual positive and negative system
3. 3 structural genes: araB, araA, and araD
4. Encode the metabolic enzymes for breaking down arabinose for further metabolism via the HMP Shunt pathway