Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Histone acetylation and deacetylation wikipedia , lookup
Protein moonlighting wikipedia , lookup
List of types of proteins wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Transcriptional regulation wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Gene regulatory network wikipedia , lookup
GENE REGULATION GENE REGULATION Virtually every cell in your body contains a complete set of genes But they are not all turned on in every tissue Each cell in your body expresses only a small subset of genes at any time During development different cells express different sets of genes in a precisely regulated fashion GENE REGULATION Gene regulation occurs at the level of transcription or production of mRNA A given cell transcribes only a specific set of genes and not others Insulin is made by pancreatic cells CENTRAL DOGMA Genetic information always goes from DNA to RNA to protein Gene regulation has been well studied in E. coli When a bacterial cell encounters a potential food source it will manufacture the enzymes necessary to metabolize that food Gene Regulation In addition to sugars like glucose and lactose E. coli cells also require amino acids One essential aa is tryptophan. When E. coli is swimming in tryptophan (milk & poultry) it will absorb the amino acids from the media When tryptophan is not present in the media then the cell must manufacture its’ own amino acids Trp Operon E. coli uses several proteins encoded by a cluster of 5 genes to manufacture the amino acid tryptophan All 5 genes are transcribed together as a unit called an operon, which produces a single long piece of mRNA for all the genes Regulatory Gene R Inactive repressor (apo-repressor) Operon P O L E D C 5 Proteins B A RNA polymerase binds to a promoter located at the beginning of the first gene and proceeds down the DNA transcribing the genes in sequence The tryptophane gene is turned on when there is no tryptophan in the media the trp gene is a repressible gene (Genes whose expression is turned off by the presence of some substance (co-repressor)) That is when the cell wants to make its’ own tryptophan Fig. 16.6 Tryptophan Operon Absence of Tryptophan Co-repressor -tryptophan Gene expression Presence of tryptophan P O L E D C B A B A Absence of tryptophan R Inactive repressor (apo-repressor) 5 Proteins Activates repressor No gene expression Presence of Tryptophan Negative control R P O L E D C No trp mRNA Inactive repressor (apo-repressor) Trp (co-repressor) GENE REGULATION In addition to amino acids, E. coli cells also metabolize sugars in their environment In 1959 Jacques Monod and Fracois Jacob looked at the ability of E. coli cells to digest the sugar lactose GENE REGULATION In the presence of the sugar lactose, E. coli makes an enzyme called beta galactosidase Beta galactosidase breaks down the sugar lactose so the E. coli can digest it for food It is the LAC Z gene in E coli that codes for the enzyme beta galactosidase Lac Z Gene Lac Z is an inducible gene ( Genes whose expression is turned on by the presence of some substance) E. coli cells can not make the sugar lactose They can only have lactose when it is present in their environment Then they turn on genes to break down lactose GENE REGULATION The E. coli bacteria only needs beta galactosidase if there is lactose in the environment to digest There is no point in making the enzyme if there is no lactose sugar to break down It is the combination of the promoter and the DNA that regulate when a gene will be transcribed GENE REGULATION This combination of a promoter and a gene is called an OPERON Operon is a cluster of genes encoding related enzymes that are regulated together Regulatory Gene i Operon p o z y a DNA m-RNA Protein Transacetylase b-Galactosidase Permease LAC Z GENE E. coli regulate the production of Beta Galactocidase by using a regulatory protein called a repressor The repressor binds to the lac Z gene at a site between the promotor and the start of the coding sequence The site the repressor binds to is called the operator LAC Z GENE Normally the repressor sits on the operator repressing transcription of the lac Z gene In the presence of lactose the repressor binds to the sugar and this allows the polymerase to move Absence of lactose i z o p a y Active No lac mRNA Presence of lactose i p o z y a Inactive b-Galactosidase Permease Transacetylase LAC Z GENE When there is no sugar left the repressor will return to its spot on the chromosome and stop the transcription of the lac Z gene Absence of lactose i p o z y Active No lac mRNA a Negative control (bound repressor inhibits transcription) Catabolite Repression (Glucose Effect) Definition: Control of an operon by glucose Catabolic operons Units of galactosidase - glucose Glucose added + glucose Time (hr) + lactose Mechanism of Catabolite Repression Absence of glucose c-AMP CAP (CRP) protein CAP-cAMP complex Promoter activation Adenyl cyclase c-AMP ATP CAP i p z o y a Active Inactive b-Galactosidase Permease Transacetylase Maximum expression Positive control (bound activator facilitates trancription) Mechanism of Catabolite Repression Glucose:cAMP CAP (CRP) protein No CAP-cAMP complex No Promoter activation Presence of glucose Adenyl cyclase ATP X CAP i p o z y a Inactive b-Galactosidase Permease Transacetylase Low level expression GENE REGULATION In eukaryotic organisms like ourselves there are several methods of regulating protein production Most regulatory sequences are found upstream from the promoter Genes are controlled by regulatory elements in the promoter region that act like on/off switches or dimmer switches GENE REGULATION Specific transcription factors bind to these regulatory elements and regulate transcription Regulatory elements may be tissue specific and will activate their gene only in one kind of tissue Sometimes the expression of a gene requires the function of two or more different regulatory elements