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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.

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Presentation on theme: "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."— Presentation transcript:

1 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

2 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

3 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

4 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

5 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 RNA polymerase binds to a promoter located at the beginning of the first gene and proceeds down the DNA transcribing the genes in sequence

6 Fig. 16.6

7 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

8 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

9 Lac Z Gene The tryptophane gene is turned on when there is no tryptophan in the media That is when the cell wants to make its own tryptophan 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 beak down lactose

10 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

11 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

12 GENE REGULATION Operon consists of A promoter site where RNA polyerase binds and begins transcribing the message A region that makes a repressor Repressor sits on the DNA at a spot between the promoter and the gene to be transcribed This site is called the operator


14 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


16 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 down the lac Z gene

17 LAC Z GENE This results in the production of beta galactosidase which breaks down the sugar 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



20 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 one/off switches or dimmer switches

21 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

22 INTRONS AND EXONS Eukaryotic DNA differs from prokaryotic DNA it that the coding sequences along the gene are interspersed with noncoding sequences The coding sequences are called EXONS The non coding sequences are called INTRONS

23 INTRONS AND EXONS After the initial transcript is produced the introns are spliced out to form the completed message ready for translation Introns can be very large and numerous, so some genes are much bigger than the final processed mRNA

24 INTRONS AND EXONS Muscular dystrophy DMD gene is about 2.5 million base pairs long Has more than 70 introns The final mRNA is only about 17,000 base pairs long

25 RNA Splicing Provides a point where the expression of a gene can be controlled Exons can be spliced together in different ways This allows a variety of different polypeptides to be assembled from the same gene Alternate splicing is common in insects and vertebrates, where 2 or 3 different proteins are produced from one gene



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