genitics and molecular biology

1. Gene expression in
prokaryotes

2.  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

3.  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

4. Rod-Shaped Bacterium,
Escherichia coli dividing by
binary fission
Rod-Shaped
Bacterium,
hemorrhagic E. coli,
strain

6. * * * * *
Type B

7.  Inducible gene
− Regulated by inducer/activator
 Constitutive gene
− Not subjected to regulation

8.  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

9.  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

10.  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)

11.  Inducible system
 Three genes part of an operon that code for
three separate enzymes
 Needed for the breakdown of lactose, a
simple sugar

13. Lac I
Promoter
gene
Operator
gene
Lac Z Lac Y Lac A
RNA polymerase
Repressor
tetramer
R
Translation &
Transcription
Inactive
repressor
Desired
product

14. Lac I
Promoter
gene
Operator
gene
Lac Z Lac Y Lac A
R
Translation &
Transcription
RNA polymerase
No Gene
Expressio
n

15. Lac I
Promoter
gene
Operator
gene
Lac Z Lac Y Lac A
mRNA
R R
RR
Lactose absentRepressor
molecules
Repressor
tetramer
No Gene
Expressio
n
RNA polymerase

16. Lac I
Promoter
gene
Operator
gene
Lac Z Lac Y Lac A
mRNA
R R
RR
RNA polymerase
mRNA
Thiogalact
oside
transacetyl
ase
Permeas
e
β-
galactosidase Inducer
Inactive repressor
R
Lactose/
Isopropyl
Thiogalactosid
e (IPTG)
present

17. If there occurs no glucose metabolism

18. 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
β-galactosidase
Permease
Thiogalactoside
transacetylase
If there occurs glucose metabolism
R
IR
I

19. Trp Operon Model
Trp
A
Trp C
Trp
B
Trp LP/O Trp E Trp D

21. Tryptoph
an
synthetas
e (B
protein)
Tryptopha
n
synthetase
(A protein)
Anthranil
ate
synthetas
e
Anthranil
ate
synthetas
e
Glycerol-
phosphate
synthetase

23. 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