Gene expression & its regulation.

This presentation provide knowledge about Gene Expression & its regulation in brief.
i hope it gives some information about gene expression in your academic time.
In this presentation mentioned - Lac Operon and its expressor.

1. Seminar on Gene Expression & Its Regulation Presented by Moh.Uzai r M.Pharm(Pharmacology) I st Semester Student SPER, Jamia Hamdard New Delhi

2. Contents 1. Gene. 1 2. Gene Expression. 2 a)Replication 5-6 b) Transcription 7-8 c) Translation 9-10 3. Regulation of Gene Expression. 11 4. Types of Gene Regulation. 12-13 a)Positive Regulation b) Negative Regulation

3. Contents 5. Types of Genes. 14-15 a) Constitutive Genes b) Inducible Genes 6.Regulation of Gene Expression in Prokaryotes. 16-24 Operon . Lac Operon 7.References. 25

4. 1.Gene Gene is a small piece of genetic material written in a code and called DNA. Gene is passed from parents to child. Genes determines the child’s characteristics - like hair,eye,skin color, height and whether the child will have an inherited disease. 1

5. 2.Gene Expression Gene expression refers to multistep process that results in production of structural & functional unit of cell called protein. Gene Expression is the combined process of the transcription of a gene into mRNA & its translation into protein. The first step is DNA RNAmRNAProtein. Gene Expression = Transcription+ Translation 2

6. Gene Expression Genetic mutation alters the regulation or expression of gene and results in dysfunctional and non functional protein synthesis. Non protein coding genes are not translated. Multistep process is also called Central Dogma. Central Dogma is the flow of information from DNA to RNA & then to Protein. 3

7. Gene Expression is a multistep process which involves a) Replication b) Transcription c) Translation 4 Moh.Uzair

8. a) Replication(DNA Synthesis) The duplication or synthesis of DNA is called replication . It is occurs in S-phase of cell cycle. All over the body replication process found in same way, but Transcription process have different cell to cell. Replication process is semi-conservative means the mechanism of DNA replication that leads to a daughter molecule with one old strand and one new strand. 5

9. Replicating fork 6

10. b) Transcription It is synthesis of RNA from DNA that results in the transfer of the information stored in double stranded DNA to Single stranded RNA. Enzyme involved is RNA Polymerase. During transcription, only one strand of DNA is usually copied. This is called the template strand, and the RNA molecules produced are single-stranded messenger RNA (mRNAs). 7

11. Transcription 8

12. c) Translation(Protein biosynthesis) Protein biosynthesis is called translation. It is found in Ribosomes(free/ cytosolic) mRNA is translated in 5’ to 3’direction. Protein is synthesized from amino terminal(N-terminal ) to carboxy terminal(c-terminal). All amino acids should be present at the time of translation otherwise translation will stop at codons. tRNA is required for translation & accept the amino acid in protein synthesis 9

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14. 3.Regulation of Gene Expression Regulation of gene expression is essential for metabolic functions, growth and development and differentiation of tissues. The rate of expression of prokaryotic(bacteria) genes is controlled mainly at the level of transcription, mRNA synthesis. Eukaryotes however have a much larger and more complex genome than prokaryotes. 11

15. 4.Types of Gene Regulation a) Positive regulation b) Negative regulation a) Positive Regulation : Gene expression is increased by a regulatory element. The element or molecule mediating the positive regulation is said to be an activator or inducer. 12

16. Types of Gene Regulation b) Negative Regulation : Gene expression is decreased by regulatory element is said to be a negative regulator( repressor/inhibitor ). Double negative effect on gene regulation results in a positive phenomenon. 13

17. 5.Types of genes a) Constitutive / housekeeping genes: Always active. They form products(proteins/ enzymes) which is required for basic cell function all the time. It is the genes whose expression is not regulated. These genes are expressed at a constant rate. E.g. The enzymes of citric acid cycle. 14

18. Types of genes b) Inducible Genes : It is expressed only in special circumstances. E.g. This genes synthesize the enzymes of gluconeogenesis which is not required in normal situation(fed state).So these genes are inhibited in a normal situation. But it required (e.g. during fasting/starvation), these genes are activated. It is regulated by various molecular signals that is why it is known as Regulated Genes. 15

19. 6. REGULATION OF GENE EXPRESSION. operon In prokaryotes, the genes involved in a metabolic pathway are often present in a linear fashion, called an operon. Operon is functioning unit of DNA containing a cluster of genes, under the control of a single promoter. Transcription is the main site of regulation of gene expression. 16

20. Operons occur in prokaryotes but not in eukaryotes. For example: • Lactose operon ( Lac operon for regulation of lactose metabolism) • Arabinose operon (Ara operon for regulation of arabinose metabolism) • Galactose operon (Gal operon for regulation of galactose metabolism). 17

21. Lac Operon/ Lactose Operon The concept of operon was introduced by Jacob and Monod in 1961. It is occurs in E.coli. Bacterial cell normally get energy from glucose because glucose is mostly present in the environment of E.coli . There is no need for this bacterial to cell use lactose. So these genes (synthesize the enzymes of lactose metabolism) are inhibited(repressed).But if required, these genes can be activated(induced). 18

22. It is consists of a regulatory gene(I; I for inhibition), operator gene (O) and 3 structural genes(Z,Y,A). Lac Z- codes for Beta Galactosidase  breaks Lactose to Galactose and Glucose Lac Y- codes for permease  facilitate permeation of Lactose into the cell. Lac A-Codes for Transacetylase  acetylates lactose. 19

23. How Genes are Inhibited 20 Lac I is a house keeping gene(always active).So, this gene always produces its protein i.e. repressor tetramer. This repressor tetramer goes and binds with operator site on DNA. Upstream to operator, promotor is present where RNA polymerase binds. Repressor tetramer gives hindrance in the path of RNA polymerase, which has to move downstream to transcribe these

24. 21 Genes for lactose metabolism. So these genes are inhibited.

25. How Genes are Activated 22 These genes are activated if glucose decreases in the environment of E. coli and lactose is present. So when glucose decreases then cAMP is increased. This cAMP binds with CAP(Catabolic Activator Protein also known as CRP i.e. cAMP Regulatory Protein) & makes cAMP -CAP complex. This complex binds to CAP site on DNA and activates RNA polymerase.

26. Lactose is converted to its isomer- Allolactose , which binds to repressor tetramer and removes repressor tetramer from operator site. So, there is no hindrance of repressor tetramer and RNA polymerase is active. Now genes are activated and transcription occurs and lactose can be used by bacterial cell. 23

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28. 7. References Harper’s Illustrated Biochemistry 30 th edition The McGraw-Hill Companies, Page No. 371-431 Lippincott Williams & Wilkins|Wolters Kluwer 4 th edition, Page No. 437 Essentials of Biochemistry by Pankaja Naik 2 nd edition, Jaypee Brothers Medical Publishers, Page No.355-356 Biochemistry by U.Satyanarayana 4 th edition, Elsevier Publication, Page No.566-567 https://www.topperlearning.com/doubts-solutions/what-is-lac-operon-in-briefly-zimbkvgg 25