Gene-Regulation-Lac-Operon-Trp-Operon.ppt

Dry-bulb temperature: The temperature of the air, as measured by a thermometer
Humidity ratio: The amount of water in the air relative to the amount of dry air
Wet-bulb temperature: Another temperature measurement of the air
Dew-point temperature: The temperature at which water will start to condense
Enthalpy: A measurement of heat energy in the air
Specific volume: A measurement of air density
How to use a psychrometric chart
Locate the point where your known measurements intersect on the chart
Use a ruler to follow the lines extending from that point to the various scales on the chart
Read the other measurements from the scales
Applications
You can use a psychrometric chart to: troubleshoot environmental problems in greenhouses and livestock buildings, assess psychrometric processes, and find practical solutions.
Psychrometric Chart Use
12 Jul 2023

Penn State Extension
Psychrometrics - Wikipedia
A psychrometric chart is a graph of the thermodynamic parameters of moist air at a constant pressure, often equated to an elevation relative to sea level. The A...

Wikipedia

1. 03/05/25 1
GENE REGULATION
Lac Operon &Trp Operon
in
Bacteria
Dr. Raghvendra Dubey

2. 03/05/25 2
Gene Regulation
•Gene Regulation refers to the processes that
cells use to turn the information on genes into
gene products.
•This functional gene product may be RNA or
Protein & the majority of known mechanisms
regulate protein coding genes.
•Gene regulation is essential for viruses,
prokaryotes & eukaryotes as it increases the
versatility & adaptability of an organism by
allowing the cell to express protein when needed.
•The first example of gene regulation system was
the lac operon, discovered by Jacob & Monod, in
which protein involved in lactose metabolism are
expressed by E.coli only in the presence of
lactose and absence of glucose.

3. 03/05/25 3
June 1961 - Lac Operon
•Jacques Monod (born February 9, 1910 – May 31,
1976 in Paris) : A French biologist , Awarded
Nobel Prize in Physiology/ Medicine in 1965.
•François Jacob (born 17 June 1920 in Nancy,
France)
•Famous for their work on the Lac operon
•Jacob F; Monod J (June 1961) "Genetic
regulatory mechanisms in the synthesis of
proteins". J Mol Biol. 3: 318–56.

4. 03/05/25 4
What is Lac Operon
•Lac Operon is an Operon required for the
transport and metabolism of lactose in
Escherichia coli and some other enteric
bacteria.
•Consists of 3 adjacent structural genes, a
promoter, an operator, a regulator and a
terminator.
•Regulated by several factors including the
availability of glucose and of lactose.

5. 03/05/25 5
Structure of the Operon
•Lac operon consists of 3 structural genes, a
promoter, an operator, a regulator and a
terminator. They are lacZ, lacY, and lacA.
•lacZ encodes β-galactosidase (LacZ): An
intracellular enzyme that cleaves the
disaccharide lactose into glucose and galactose.
•lacY encodes β-galactoside permease (LacY)- a
membrane-bound transport protein that pumps
lactose into the cell.
•lacA encodes β-galactoside transacetylase
(LacA)- an enzyme that transfers an acetyl
group from acetyl-CoA to β-galactosides.
•Only lacZ and lacY appear to be necessary for
lactose catabolism.

6. 03/05/25 6
•Specific control of the lac genes depends on the
availability of the substrate lactose to the
bacterium.
•The proteins are not produced by the bacterium
when lactose is unavailable as a carbon source.
•The lac genes are organized into an operon;
they are oriented in the same direction
immediately adjacent on the chromosome and
are co-transcribed into a single polycistronic
mRNA molecule.
•Transcription of all genes starts with the binding
of the enzyme RNA polymerase (RNAP).

7. 03/05/25 7
Lac Operon Organization
•3 structural genes involved in lactose
metabolism in E.coli
•These lac genes are organized into the lac
Operon
•An Operon is a cluster of genes along with
an adjacent promoter & operator that
control the transcription

8. 03/05/25 8
Structural Gene Transcription
A Single mRNA is Produced

9. 03/05/25 9
Polycistronic mRNA - Because it carries the information for more than
one type of protein
Lac Z
+
Lac Y
+
Lac A
+
Breaks down lactose
into glucose & galactose
Transports lactose
into the cell
Not fully understood

10. 03/05/25 10
Lac Operator
Lac O+ is a short region of DNA that lies
partially within the promoter
It interacts with the regulatory protein that
controls the transcription of the Operon.

11. 03/05/25 11
Lac Regulatory
Lac I
+
produces an mRNA & synthesized a repressor protein
The lac regulatory protein is called a repressor
because it keeps RNA polymerase from
transcribing the structural gene
This repressor protein can bind to the
operator of the lac operon

12. 03/05/25 12
In Absence of Lactose
In the absence of lactose, lac
repressors binds to the operator

13. 03/05/25 13
In Presence of Lactose
Small amount of it are converted into
Binds
Changed its Shape &
cannot bind to the
promoter

14. 03/05/25 14
Positive Control of Lac Operon

15. 03/05/25 15
Catabolite Repression

16. 03/05/25 16

17. 03/05/25 17
Trp Operon
•Trp Operon is an operon in bacteria which
promotes the production of tryptophan
when tryptophan isn't present in the
environment.
•First repressible operon to be discovered.
•If the amino acid is present, then the
operon is repressed & biosynthetic
enzymes are not produced.

18. 03/05/25 18
Trp Operon
Consists of Regulatory & Structural Genes
5 Structural Genes – trpE to trpA (Downstream) of Promoter Region
Transcribed as Polycistronic mRNA – Responsible for tryptophan biosynthesis
Promoter & Operator region regulates the level of transcription

19. 03/05/25 19
Between the Promoter/Operator & the Structural gene
is the Leader Region, trpL
Transcribed into an mRNA called – Leader mRNA
Contains a short ORF & translated into a leader peptide

20. 03/05/25 20
Leader mRNA contains the Attenuator consisting of 4 regions
(1,2,3 &4) that fold & forms 3 different loop secondary structure.
1 & 2 pairing
results in
transcription
pause signal
2 & 3 pairing results in an antitermination
signal that allows transcription to continue
3 & 4 pairing results in a
termination signal which
stops further transcription

21. 03/05/25 21
Since there is no nuclear membrane in bacteria
transcription & translation occur at the same time
Translation of trpL mRNA proceeds
while RNAP transcribe the attenuator
mRNA
After RNAP has transcribed region 2, regions 1
& 2 pair to form a stem loop structure.
This structure causes RNAP to pause & allows the ribosome
o catch up to it. Transcription is tightly coupled with translation
Ribosome’s position along the
leader mRNA plays an important
role in the regulation of
transcription

22. 03/05/25 22
Trp Starved
When the cell is starved for Trp, the amount of Trp-tRNA drops
dramatically. In the leader mRNA there are 2 Trp codons in tandem. When
the ribosome reaches these codons, it stalls because the amino acid is
short supply & the leader peptide cannot be completed.
Since the ribosome covers region1 of the attenuator, region2 will pair with
region3. This pairing is an antitermination signal, thereby allowing RNAP to
proceed & translation follows to synthesize enzymes necessary to produce trp

23. 03/05/25 23
When the cell is not starved for
tryptophan, there is enough
Trp-tRNA for translation
When the ribosome reaches
the 2 Trp codons , 2 Trps are
added to the leader peptide.
The ribosome then continues
to the stop codon at the end of
region 1 of the leader peptide.
This prevents region2 from
pairing with 3
Instead region 3 pairs with 4 which is a termination signal fort RNAP

24. 03/05/25 24
The key signal for attenuation is the conc
n
of Trp-tRNA gene in the cell
If there is an abundance of Trp & Trp-tRNA, then a short leader mRNA
transcript is synthesized & transcription is then terminated
No Tryptophan biosynthesis enzymes are made
If the cell is deficient in Trp & Trp-tRNA , then RNAP continues transcription
past trpL & through the 5 trp genes. Ribosome translate this polygenic mRNA
to produce the enzymes for Tryptophan biosynthesis