08 lac operon
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The lac operon controls genes involved in lactose metabolism in E. coli bacteria. It consists of three genes that are transcribed together. When glucose is present, a repressor protein binds to the operator site of the lac operon and blocks transcription. When lactose is present, an allosteric change in the repressor protein causes it to detach from the operator site, allowing RNA polymerase to bind and transcribe the genes. However, in the presence of both glucose and lactose, transcription does not occur as RNA polymerase is unstable and falls off the promoter site readily. Only when glucose is absent and lactose is present, an activator protein binds and stabilizes RNA polymerase, leading to efficient transcription of the lac oper
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DNA is the genetic material found in chromosomes inside cells. It contains the biological instructions that determine traits like eye color. DNA is made of nucleotides with a phosphate group, sugar (deoxyribose), and one of four nitrogenous bases: adenine, guanine, cytosine, or thymine. DNA exists as two strands coiled around each other in the famous double helix structure, with the bases on one strand pairing with their complements on the other strand. Molecular techniques use DNA, RNA, and enzymes to study biology at a molecular level and detect disease states.
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The document provides information on the basics of molecular biology. It begins with a table comparing key attributes of eukaryotes and prokaryotes. It then defines molecular biology as the study of the molecular underpinnings of processes like DNA replication, transcription, and translation. The basic components involved are described as DNA, RNA, and proteins. DNA stores genetic information. RNA and proteins are involved in building and regulating cells. The processes of DNA replication, transcription, translation, and their roles are summarized.
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Lac operon
lac operon is one of the most important topic for UG and PG students and also from the competitive point of view.
Biochem gene expression regulation(29.6.10)
The document discusses gene regulation and provides examples in bacteria. It explains that certain genes are turned on or off depending on environmental factors. It describes the lac operon in E. coli, which contains genes involved in processing the sugar lactose. The lac operon is regulated by the presence of lactose and glucose such that the genes are only expressed when glucose is absent and lactose is present.
08 lac operon
The lac operon controls genes involved in lactose metabolism in E. coli bacteria. It consists of three structural genes - lacZ, lacY, and lacA - that encode enzymes for breaking down lactose. The operon is regulated by a repressor protein that binds to the operator region and blocks transcription when glucose is present. In the absence of glucose but presence of lactose, an allolactose molecule causes a shape change in the repressor, releasing it from the DNA and allowing transcription. For transcription to occur when both glucose and lactose are present, a catabolite activator protein is also required to stabilize the binding of RNA polymerase to the promoter.
OPERONS- KHZ 2023.ppt
The document discusses gene regulation and operons. It covers:
1. Operons are groups of genes transcribed together in prokaryotes to control important processes. The lac operon in E. coli contains genes for lactose metabolism.
2. The lac operon is regulated by a repressor protein that binds to the operator site and blocks transcription unless the inducer allolactose is present.
3. Eukaryotic gene regulation has multiple levels including chromatin remodeling, histone modification through methylation and acetylation, and transcription factor regulation.
lac Operon.pdf
1. The lac operon encodes three genes involved in lactose metabolism in E. coli and is regulated by the presence of lactose and glucose.
2. In the absence of lactose, a repressor protein binds to the operator site and blocks transcription of the lac genes.
3. When lactose is present, it binds to the repressor protein causing a conformational change that prevents it from binding to the operator, allowing transcription.
Regulation of Gene expression.pdf
1. Gene expression is regulated differently in prokaryotes and eukaryotes. Prokaryotes use operons to regulate groups of genes, while eukaryotes have more complex nuclear-based regulation.
2. The lac operon in E. coli regulates genes for lactose metabolism. It is turned on in the presence of lactose and absence of glucose through a repressor protein that binds DNA and an activator protein that stabilizes RNA polymerase.
3. The lac operon includes genes for the enzyme beta-galactosidase which breaks down lactose. A repressor protein binds the operator site and blocks transcription unless removed by the sugar allolactose in the presence of lact
operon_lac_and_trp_in_ bacteria.ppt
Gene expression is tightly regulated through various mechanisms in both prokaryotes and eukaryotes. In prokaryotes, genes are often organized into operons and regulated together. The lac operon in E. coli contains three genes involved in lactose metabolism that are regulated by a repressor protein. In the absence of lactose, the repressor binds to the operator region and blocks transcription. When lactose is present, it is converted to allolactose, which binds to the repressor and causes a conformational change that prevents it from binding to the operator, allowing transcription to proceed. This provides an example of negative and inducible gene regulation.
Regulation of gene expression
This document discusses the regulation of gene expression. It defines key terms like gene, genome, and gene expression. It explains that some genes are expressed continuously while others are only expressed under certain conditions. There are mechanisms that allow cells to express or turn off certain genes as needed. Regulation of gene expression is essential for optimal energy use and the growth, development, and existence of organisms. There are two main types of regulation: positive regulation which increases gene expression, and negative regulation which decreases it. The document then focuses on prokaryotic gene expression, explaining operons as groups of genes expressed together from a single promoter. It provides the example of the lac operon in E. coli, which expresses genes for lactose metabolism
Operon Modal of Gene Regulation
Each cell of a multicellular organism contain the same genetic material, but the expression of the gene is different in different type of cell group. On the basis of expression requirement they are grouped in to
Structural Gene- Mostly expressed once in a life
Vital Gene- Involved in of vital biochemical processes such as respiration and need to be expressed all the time
Functional Gene- Genes are not expressed all the time. They are switched on an off at need
The regulation of Gene required in case of functional gene and its explained by Francois Jacob, Jacques Monod and Andre Lwoff (Nobal Prize in 1961)
Lac operon
This document summarizes the lac operon in E. coli, which regulates genes involved in lactose metabolism. The lac operon contains structural genes that encode beta-galactosidase, galactoside permease, and thiogalactoside transacetylase. These genes are regulated by a repressor protein that binds to the operator region and prevents transcription under non-inducing conditions when lactose is absent. However, in the presence of lactose, allolactose is produced and binds to the repressor, causing a conformational change that prevents it from binding to the operator. This allows RNA polymerase to bind to the promoter and initiate transcription of the structural genes, allowing lactose to be metabol
Molecular Genetics_Lac operon .ppt
The document discusses gene expression in prokaryotes through the lac operon in E. coli. It explains that the lac operon consists of three genes involved in lactose metabolism regulated by a single promoter. When glucose is absent and lactose is present, an activator protein binds to DNA, lifting the repressor protein off the operator site and allowing RNA polymerase to transcribe the lac operon. When glucose is present, the repressor protein binds to the operator site, blocking transcription of the lac operon.
Lac operon overall
The document discusses the lac operon in bacteria. The lac operon is a cluster of genes involved in lactose metabolism. It includes three structural genes that encode enzymes for breaking down lactose. The operon is induced in the presence of lactose and repressed in its absence by a lac repressor protein. The lac operon demonstrates how bacteria efficiently regulate gene expression in response to environmental conditions through an inducible operon system.
LAC OPERON.pptx
The document discusses gene regulation in prokaryotes using the lac operon in E. coli as an example. The lac operon consists of structural genes that encode proteins for lactose metabolism and regulatory genes that control their expression. In the absence of lactose, a repressor protein binds to the operator region and prevents transcription. When lactose is present, it is converted to allolactose which binds the repressor and prevents it from binding the operator, allowing transcription. The presence of glucose inhibits transcription through a mechanism involving cAMP and the catabolite activator protein.
Lac operon
lac operon is a negatively controlled inducible operon.E.coli can use lactose as a source of carbon.
The enzymes required for the use of lactose as a source of carbon are synthesised only when the lactose is available as carbon source.
The lac operon is an example of nagatively controlled inducible operon.
Structure
The lac operon consists of 5 structural units.
Promoter
Operator
Structural genes
CAP binding sites
Regulatory gene
Prokaryotic expression system
The document discusses prokaryotic expression systems, which are genetic constructs used to produce proteins or RNA inside or outside cells. It focuses on the prokaryotic system, which is most widely used for recombinant protein production in E. coli bacteria. Key aspects covered include the history of prokaryotic expression research, types of gene regulation like operons and regulatory molecules, examples of operons like the lac and trp operons, and differences between prokaryotic and eukaryotic gene expression.
Lecture Merodiploids -lac genes_slideshare.pdf
The document discusses the use of merodiploids, or partially diploid prokaryotes, in studying gene mutations in the lac operon in E. coli. Merodiploids contain two copies of certain genes, which allows researchers to examine how wild-type and mutated alleles interact. A series of examples are provided to illustrate how different mutations in the lac operon's operator, repressor, and promoter regions would affect the production of beta-galactosidase and permease in merodiploid E. coli under varying conditions.
Lac operon model
The lac operon allows E. coli to metabolize lactose as an energy source when glucose is unavailable. It contains three structural genes—lacZ, lacY, and lacA—that are expressed together under the control of a single promoter. When lactose is present, it binds to the lac repressor and induces expression of the genes. However, in the presence of glucose, catabolite repression by cAMP prevents expression even if lactose is available. The lac operon was the first genetic regulatory mechanism to be understood and demonstrated negative regulation through a repressor protein.
6.gene expression
The document summarizes key concepts about gene regulation and expression in bacteria and eukaryotes. It discusses how the lac and trp operons in E. coli are regulated through induction/repression and feedback inhibition. It also notes that while eukaryotes use similar processes, gene expression is more complex due to differences in gene organization and chromatin-based regulation rather than operons.
GENE REGULATION IN PROKARYOTES AND EUKARYOTES
1. Gene regulation in prokaryotes and eukaryotes involves control at the levels of transcription and translation.
2. In prokaryotes, genes are often organized into operons and regulated through inducible and repressible operons controlled by regulatory proteins binding to operator and promoter sites. The lac and trp operons are examples of inducible and repressible operons, respectively.
3. In eukaryotes, gene expression is controlled through chromatin structure, transcriptional initiation, transcript processing and modification, transport, stability, and small RNA-mediated pathways. This allows for complex tissue-specific and developmental control of gene expression.
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08 lac operon
- 1. THE lac OPERON © 2007 Paul Billiet ODWS
- 2. The control of gene expression Each cell in the human contains all the genetic material for the growth and development of a human Some of these genes will be need to be expressed all the time These are the genes that are involved in of vital biochemical processes such as respiration Other genes are not expressed all the time They are switched on an off at need © 2007 Paul Billiet ODWS
- 3. Operons An operon is a group of genes that are transcribed at the same time. They usually control an important biochemical process. They are only found in prokaryotes. © 2007 Paul Billiet ODWS Jacob, Monod & Lwoff © NobelPrize.org
- 4. The lac Operon • • • The lac operon consists of three genes each involved in processing the sugar lactose One of them is the gene for the enzyme βgalactosidase This enzyme hydrolyses lactose into glucose and galactose © 2007 Paul Billiet ODWS
- 5. Adapting to the environment E. coli can use either glucose, which is a monosaccharide, or lactose, which is a disaccharide However, lactose needs to be hydrolysed (digested) first So the bacterium prefers to use glucose when it can © 2007 Paul Billiet ODWS
- 6. Four situations are possible 1. When glucose is present and lactose is absent the E. coli does not produce β-galactosidase. 2. When glucose is present and lactose is present the E. coli does not produce β-galactosidase. 3. When glucose is absent and lactose is absent the E. coli does not produce β-galactosidase. 4. When glucose is absent and lactose is present the E. coli does produce β-galactosidase © 2007 Paul Billiet ODWS
- 7. The control of the lac operon © 2007 Paul Billiet ODWS
- 8. 1. When lactose is absent A repressor protein is continuously synthesised. It sits on a sequence of DNA just in front of the lac operon, the Operator site The repressor protein blocks the Promoter site where the RNA polymerase settles before it starts transcribing Repressor protein DNA I O Regulator gene Operator site © 2007 Paul Billiet ODWS RNA polymerase Blocked z y lac operon a
- 9. 2. When lactose is present A small amount of a sugar allolactose is formed within the bacterial cell. This fits onto the repressor protein at another active site (allosteric site) This causes the repressor protein to change its shape (a conformational change). It can no longer sit on the operator site. RNA polymerase can now reach its promoter site DNA I © 2007 Paul Billiet ODWS O z y a
- 10. 2. When lactose is present A small amount of a sugar allolactose is formed within the bacterial cell. This fits onto the repressor protein at another active site (allosteric site) This causes the repressor protein to change its shape (a conformational change). It can no longer sit on the operator site. RNA polymerase can now reach its promoter site DNA I © 2007 Paul Billiet ODWS O z y Promotor site a
- 11. 3. When both glucose and lactose are present This explains how the lac operon is transcribed only when lactose is present. BUT….. this does not explain why the operon is not transcribed when both glucose and lactose are present. © 2007 Paul Billiet ODWS
- 12. When glucose and lactose are present RNA polymerase can sit on the promoter site but it is unstable and it keeps falling off Repressor protein removed RNA polymerase DNA I O z y Promotor site a
- 13. 4. When glucose is absent and lactose is present Another protein is needed, an activator protein. This stabilises RNA polymerase. The activator protein only works when glucose is absent In this way E. coli only makes enzymes to metabolise other sugars in the absence of glucose Activator protein steadies the RNA polymerase Transcription DNA I O z y Promotor site © 2007 Paul Billiet ODWS a
- 14. Summary Carbohydrates Activator protein Repressor protein RNA polymerase lac Operon + GLUCOSE + LACTOSE Not bound to DNA Lifted off operator site Keeps falling off promoter site No transcription + GLUCOSE - LACTOSE Not bound to DNA Bound to operator site Blocked by the repressor No transcription - GLUCOSE - LACTOSE Bound to DNA Bound to operator site Blocked by the repressor No transcription - GLUCOSE + LACTOSE Bound to DNA Lifted off Sits on the operator site promoter site © 2007 Paul Billiet ODWS Transcription