Transcript Online Counseling Resource YCMOU ELearning Drive…

Online Counseling Resource
YCMOU ELearning Drive…
School of Architecture, Science and Technology
Yashwantrao Chavan Maharashtra
Open University, Nashik – 422222, India
SEP–SBI082–U01-04
Introduction
Programmes and Courses
 SEP–SBI082–Unit 01-CP1
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Credits
 Academic Inputs by
Sonali Alkari
Counsellor, YCMOU Nagpur Centre,
Faculty LAD college P.G. D of Biotechnology
Research officer Ankur Seeds Pvt Ltd
[email protected]
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How to Use This Resource

Counselor at each study center should use this presentation to deliver
lecture of 40-60 minutes during Face-To-Face counseling.

Discussion about students difficulties or tutorial with assignments should
follow the lecture for about 40-60 minutes.

Handouts (with 6 slides on each A4 size page) of this presentation should
be provided to each student.

Each student should discuss on the discussion forum all the terms which
could not be understood. This will improve his writing skills and enhance
knowledge level about topics, which shall be immensely useful for end
exam.

Appear several times, for all the Self-Tests, available for this course.

Student can use handouts for last minutes preparation just before end
exam.
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Learning Objectives
After studying this module, you should be able to:
 Explain an inducible system ?
 Explain structural genes of lac operon
 Explain Regulation of Lac operon.
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Operon Gene Regulation
 Control of operon genes is a type of gene
regulation that enables organisms to regulate the
expression of various genes depending on
environmental conditions.
 Operon regulation can be:
 negative
 positive.
 Negative regulation involves the binding of a
repressor to the operator to prevent transcription.
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The lac Operon – An Inducible System
 The first control system for enzyme production
worked out at the molecular level described the
control of enzymes that are produced in response
to the presence of the sugar lactose in E. coli cell.
 The work was performed by Jacob and Monod for
which they were awarded the Nobel Prize.
 Lactose is a sugar found in milk.
 If lactose is present, E. coli (the common intestinal
bacterium) needs to produce the necessary
enzymes to digest it.
 Three different enzymes are needed.
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The lac Operon - 1
 In the diagrams below, genes A, B, and C represent
the genes whose products are necessary to digest
lactose.
 In the normal condition, the genes do not function
because a repressor protein is active and bound to the
DNA preventing transcription.
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The lac Operon-2
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The lac Operon - 3
 When the repressor protein is bound to the
DNA, RNA polymerase cannot bind to the
DNA.
 The protein must be removed before the
genes can be transcribed.
 The lac operon is an example of an inducible
operon because the structural genes are
normally inactive.
 They are activated when lactose is present.
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The lac Operon - 4
 The repressor protein is produced by a regulator gene.
 The region of DNA where the repressor protein binds is the
operator site.
 The promoter site is a region of DNA where RNA polymerase
can bind.
 The entire unit (promoter, operator, and genes) is an operon.
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The lac Operon - 5
 The lac operon consists of three structural
genes:
 lacZ
codes
for
b-galactosidase.
 The lacZ gene is 3510 bp in length.
 The b-galactosidase enzyme, with a subunit
molecular weight of 125 KDal, is one of the
largest polypeptides in the E. coli cell -- 1021
amino acids.
 The active form of the enzyme is a tetramer.
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The lac Operon - 6
 lacY
codes
for
b-galactoside
permease.
The lacY gene is 780 bp in length and codes for a
30 KDal monomeric membrane protein of 260
amino acids.
 lacA codes for Thiogalactoside transacetylase.
The lacA gene is 825 bp in length and codes for a
dimeric protein, with subunit polypeptide of length
275 amino acids.
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The lac Operon - 7
 Regulator Gene
 The lac operon has one regulatory gene: lacI
which codes for the regulatory protein,
lactose repressor.
 Regulator genes code for diffusible molecules
which can potentially act at many other
locations in the genome
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The lac Operon
:Gene Organization:1
 The three structural genes are organized as
a unit lacZ-lacY-lacA and are expressed as a
unit from lacZ through lacA.
 In the lac operon, the regulator gene, lacI,
is located immediately adjacent to and
upstream of the structural genes.
 This is not a required feature of the operon
model of gene expression.
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The lac Operon
:Gene Organization:2
 There are many operons in which the
regulator gene is located far away from the
structural genes whose expression it
regulates.
 For example, the galR gene is located
halfway round the E. coli chromosome from
the galETK operon whose expression it
regulates.
 Regulator
genes
code
for
diffusible
molecules.
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The lac Operon - 1
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The lac Operon - 2
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The lac Operon - 3
 The lac operon also consists of 3 cis-acting sites:
 Three operators.
In addition to the original operator -- now named
O1 -- centred at +11,
 Two other operators have been identified which
contribute to repression in the lac system.
 O2 is located within the lacZ gene and is centred
401 bp downstream from the startpoint of
transcription.
 O3 is located immediately downstream of lacI and is
centred at position -82 with respect to the start
point of transcription.
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The lac Operon - 4
 Two promoters
A second promoter -- lacP2 -- has been
described 22 bp upstream of the original lac
promoter. The function of this promoter is
not clear.
 One CRP-binding site
CRP binds immediately upstream of the
promoter. A CLASS I CRP-binding site is
centred 61.5 bp upstream from the
startpoint of transcription
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Regulation:1
 In the absence of an inducer, the structural genes
of the operon will not be expressed because
repressor will be synthesized, it will form tetramers,
and they will bind to the operator to prevent
expression of the structural genes.
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Regulation:2
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Regulation:3
 Note that the lacI gene is expressed from its own
promoter.
 The lacI promoter is a very weak promoter so the
amount of mRNA transcribed, and, hence, the
amount of protein made, will be low.
 In the presence of an inducer, the repressor is
converted into a form that cannot bind to DNA.
 RNA polymerase bound to the lac promoter will
transcribe the three genes of the operon.
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Regulation:4
 The lac promoter is a medium strength
promoter so the amount of lac operon
mRNA made and, hence, the amount of the
protein products will be moderate.
 A key aspect of the lactose repressor and its
function are its dual properties:
 It
binds
to
DNA
(viz.
the
operator)
 It binds to the inducer.
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What You Learn…
 The lac Operon is an inducible system because the
structural genes are normally inactive.
 The repressor protein is produced by a
regulator gene.
 The lac operon consists of three structural
genes: lacZ-lacY-lacA .
 The lac operon has one regulatory gene: lacI
 The lac operon also consists of Three operators
O1,O2,O3.
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Critical Thinking Questions
1. Give an example of an inducible operon and
state why it is called so?.
2. State different kinds of regulatory genes
and structural genes present in lac Operon.
3. Decribe in details about lac Operon Operon
regulation.
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Hints For Critical Thinking Question
1. Write as short about Lac operon and
state that structural genes are
normally inactive.
2. State in details about Structural genes
lacZ-lacY-lacA and Regulator genes lacI.
3. State in detail the entire unit
(promoter, operator, and genes)and
state the role of inducer.
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Study Tips:1
 Book1
 Title:Genes IX.
 Author: Benjamin Lewin
 Publisher: Jones & Bartlett Publishers
 Book2
 Title: Genetics from Genes to Genomes
Author: L. H. Hartwell, L. Hood, M. L.
Goldberg
 Publisher: Tata McGraw-Hill
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Study Tips:2
 Book3
 Title: Genetics
 Author: Monore W.Strickberger
 Publisher: Prentice Hall of India
 Book4
 Title: Genetics
 Author: C.Serin
 Publisher: Tata McGraw-Hill
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Study Tips
www.en.wikipedia.org
Microsoft Encarta Encyclopedia
http://en.wikipedia.org/wiki/
Wikipedia the free encyclopedia
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End of the Presentation
Thank You !