Online Counseling Resource YCMOU ELearning Drive… School of Architecture, Science and Technology Yashwantrao Chavan Maharashtra Open University, Nashik – , India

Introduction Programmes and Courses  SEP–SBI082–Unit 01-CP1 SEP–SBI082–U01-04

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.3 Credits  Academic Inputs by Sonali Alkari Counsellor, YCMOU Nagpur Centre, Faculty LAD college P.G. D of Biotechnology Research officer Ankur Seeds Pvt Ltd

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.4 How to Use This Resource  Counselor at each study center should use this presentation to deliver lecture of minutes during Face-To-Face counseling.  Discussion about students difficulties or tutorial with assignments should follow the lecture for about 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.5 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.6 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.7 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.8 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.9 The lac Operon-2

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.10 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.11 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.12 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 amino acids. The active form of the enzyme is a tetramer.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.13 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.14 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

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.15 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.16 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.17 The lac Operon - 1

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.18 The lac Operon - 2

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.19 The lac Operon - 3  The lac operon also consists of 3 cis-acting sites:  Three operators. In addition to the original operator -- now named O 1 -- centred at +11,  Two other operators have been identified which contribute to repression in the lac system.  O 2 is located within the lacZ gene and is centred 401 bp downstream from the startpoint of transcription.  O 3 is located immediately downstream of lacI and is centred at position -82 with respect to the start point of transcription.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.20 The lac Operon - 4  Two promoters A second promoter -- lacP 2 -- 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

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.21 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.22 Regulation:2

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.23 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.24 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.25 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 O 1, O 2, O 3.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.26 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.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.27 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. © 2007, YCMOU. All Rights Reserved.27

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.28 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

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.29 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

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.30 Study Tips Microsoft Encarta Encyclopedia Wikipedia the free encyclopedia

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