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

SEP–SBI082–U01-05 Introduction Programmes and Courses  SEP–SBI082–CP01

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.3 Credits  Academic Inputs by Sonali Alkari Counsellor, YCMOU Nagpur Study 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 repressor system ? Explain structural genes of trp operon Explain Regulation of trp operon.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.6 Operon  There are two different kinds of genes in operons:  Structural genes code for proteins needed for the normal operation of the cell. For example, they may be proteins needed for the breakdown of sugars. The structural genes are grouped together and a single mRNA molecule is produced during their transcription.  Regulator genes code for proteins that regulate other genes. Operons have not been found in eukaryotes

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.7 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.8 Positive Inducible Operons  In positive inducible operons, activator proteins are normally unable to bind to the pertinent DNA.  However, certain substrate molecules can bind to the activator proteins and change their conformations so that they can bind to the DNA and enable transcription to take place.  In positive repressible operons, the activator proteins are normally bound to the pertinent DNA segment.  However, certain molecules can bind to the activator and prevent it from binding to DNA. This prevents transcription.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.9 Tryptophan (Trp) Operon  The trp operon is responsible for synthesizing the amino acid tryptophan.  All organisms need tryptophan in order to live. Here, when tryptophan is present the cell turns the tryptophan synthesis off because there is no need to make more.  This is, therefore, opposite from the lac operon.  On the trp operon, a repressor protein that is unable to bind to the trp operator is made. Because it does not bind to the operator, the gene is always "on."

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.10 The trp Operon  This operon contains genes for the production of five proteins which are used to produce three enzymes.  The products of the E and D genes form a multimeric protein comprised of two copies of each protein to produce the enzyme anthranilate synthetase. This enzyme catalyzes the first two reactions in the tryptophan pathway.  The next enzyme, which is responsible for catalyzing the next two steps in the pathway is indole glycerolphosphate synthetase and it is the product of the C locus.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.11 The trp Operon  The final step in the reaction is the pathway produces tryptophan from indole-glycerol phosphate and serine.  This single step is catalyzed by tryptophan synthetase, an enzyme that is a multimer of two proteins that are the product of the B and A genes.  As with all operons, the trp operon consists of the repressor, promoter, operator and the structural genes.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.12 Difference Between Repressible and Inducible Systems :1  In this system, though, unlike the lac operon, the gene for the repressor is not adjacent to the promoter, but rather is located in another part of the E. coli genome.  Another difference is that the operator resides entirely within the promoter.  The trp operon is a repressible system.  The primary difference between repressible and inducible systems is the result that occurs when the effector molecule binds to the repressor.  The lac operon is an example of an inducible system.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.13 Difference Between Repressible and Inducible Systems :2  With inducible systems, the binding of the effector molecule to the repressor greatly reduces the affinity of the repressor for the operator, the repressor is released and transcription proceeds.  With repressible systems, the binding of the effector molecule to the repressor greatly increases the affinity of repressor for the operator and the repressor binds and stops transcription.  Thus, for the trp operon, the addition of tryptophan (the effector molecule) to the E. coli environment shuts off the system because the repressors binds at the operator

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.14 The trp Operon  Repressible operons are the opposite of inducible operons.  Transcription occurs continuously and the repressor protein must be activated to stop transcription.  Tryptophan is an amino acid needed by E. coli and the genes that code for proteins that produce tryptophan are continuously transcribed as shown

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.15 Control Circuit for the trp Operon P / O | L || E | D | C | B | A | Controlling Region || Structural genes

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.16 trp Operon Gene :Gene Function P/OPromoter; operator sequence is found in the promoter trp LLeader sequence; attenuator (A) sequence is found in the leader trp EGene for anthranilate synthetase subunit trp DGene for anthranilate synthetase subunit trp CGene for glycerolphosphate synthetase trp BGene for tryptophan synthetase subunit trp AGene for tryptophan synthetase subunit

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.17 The trp Operon  If tryptophan is present in the environment, however, E. coli does not need to synthesize it and the tryptophan-synthesizing genes should be turned off.  This occurs when tryptophan binds with the repressor protein, activating it.

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

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.19 The trp Operon  Unlike the repressor discussed with the lac operon, this repressor will not bind to the DNA unless it is activated by binding with tryptophan.  Tryptophan is therefore a corepressor.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.20 The trp Operon  When trp becomes more prevalent in the cell, it will bind with the repressor and change its shape so that the repressor can bind to the operator. This stops the synthesis of the trp operon.  As the level of trp rises, more and more repressors will be able to bind to the operator and reduce trp production.  In this way, the trp operon is an elegant system that can regulate its presence in a cell.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.21 What You Learn…  The trp operon is a repressible system because the structural genes are normally active.  The trp operon consists of the repressor, promoter, operator and the structural genes  Tryptophan is therefore a corepressor.  As the level of trp rises, more and more repressors will be able to bind to the operator and reduce trp production.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.22 Critical Thinking Questions 1.Give an example of repressible system and state why it is called so?. 2.State different kinds of regulatory genes and structural genes present in trp operon. 3.Decribe in details about trp operon regulation.

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.23 Hints For Critical Thinking Question 1.Write as short about trp operon and state that structural genes are normally active. 2.State in details about repressor, promotor, operator and Structural genes of trp operon. 3.State in detail the entire unit (promoter, operator, and genes)and state the role of repressor protein © 2007, YCMOU. All Rights Reserved.23

School of Science and Technology, Online Counseling Resource… © 2007, YCMOU. All Rights Reserved.24 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.25 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.26 Study Tips Microsoft Encarta Encyclopedia Wikipedia the free encyclopedia

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