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 THIS IS A GOOD THING BECAUSE YOU DO NOT WANT HAIR TO GROW ON YOUR TONGUE OR FINGERNAILS ON YOUR FACE WE HAVE TOUCHED ON POLYGENIC TRATIS AND THOSE WITH GENETIC AND EVIRONMENTAL COMPONENTS NOW WE ARE GOING TO LOOK A BIT AT HOW DOES A CELL DECIDE WHAT KIND OF CELL IT WILL BE WHAT REGULATES WHAT GENES WILL BE TURNED ON AND OFF

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 WHAT IS MRNA? THAT IS WHY WE SPENT SO MUCH TIME ON HOW PROTEINS ARE MADE REVIEW HAVE THE INSULIN GENE IN ALL YOUR CELLS BUT IT IS ONLY EXPRESSED OR TRANSCRIBED BY CELLS IN THE PANCREASE NOT BY SKIN CELLS

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 WHY E COLI? What do you like to eat? WHEN YOU EAT YOU NEED ENZYMES TO BREAK DOWN THE FOOD YOU EAT EXPLAIN WHAT ENZYMES ARE THEY BREAK DOWN FOOD LIKE GLUCOSE AND LACTOSE WHAT ARE GLUCOSE AND LACTOSE?

E COLI REGULATE THE PRODUCTION OF B GALACTOSIDASE BY USING A REGULATORY PROTEIN CALLED A REPRESSOR THE REPRESSOR BINDS TO THE LAC Z GENE AT A SITE BETWEEN THE PROMOTER AND THE START OF THE CODING SEQUENCE THE SITE THE REPRESSOR BINDS TO IS CALLED THE OPERATOR WHEN THE REPRESSOR PROTEIN BINDS TO THE OPERATOR REGION IT BLOCKS THE POLYMERASE FROM TRANSCRIBING THE LAC Z GENE GO OVER THE SLIDE

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

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 REMEMBER THE OPERATOR WAS THE PLACE THE ACTIVATED REPRESSOR WOULD BIND TO WHEN THERE WAS TRYPTOPHAN IN THE MEDIA FOR THE LAC Z GENE THE REPRESSOR SITS ON THE DNA BETWEEN THE PROMOTOR SITE AND THE GENE AND DOES NOT ALLOW THE POLYERASE TO MOVE DOWN THE DNA MOLEUCLE AND TRANSCRIBE THE GENE

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 WHEN THE REPRESSOR PROTEIN BINDS TO THE OPERATOR REGION IT BLOCKS THE POLYMERASE FROM TRANSCRIBING THE LAC Z GENE

BETA GALACTOSIDASE IS CALLED AN INDUCIBLE ENZYME BECAUSE IT IS MADE IN RESPONSE TO A CHEMICAL WHENEVER THERE IS LACTOSE IN THE MEDIUM IT IS TAKEN UP BY THE CELL WHEN THE E COLI CELL TAKES UP LACTOSE THE LACTOSE WILL INACTIVATE THE REPRESSOR PROTEIN SO THAT IT CAN NOT BIND TO THE OPERATOR REGION SO RNA POLYMERASE CAN BIND TO THE PROMOTER REGION AND MOVE DOWN AND TRANSCRIBE THE LAC Z GENE WHEN THE GENE IS TRANSCRIBED IT PRODUCES THE BETA GALACTOSIDASE ENZYME

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

WHEN LACTOSE IS PRESENT IN THE MEDIA IT INACTIVATES THE REPRESSOR SO THE GENE CAN BE TURNED ON AND MAKE THE ENZYME THAT BREAKS DOWN LACTOSE BETA GALACTOSIDASE IS AN INDUCIBLE ENZYME BECAUSE IT IS MADE IN RESPONSE TO THE PRESENCE OF LACTOSE

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 JACOBE AND MONOD PROPOSED THIS MECHANISM IN 1959 AND SPENT THE NEXT 6 YEARS TRYING TO ISOLATE THE ELUSIVE REPRESSOR MOLECULE FROM E COLI IN ORDER TO PROVE THEIR THEORY THEY NEVER FOUND IT 1967 GILBER AND MULLER FINALLY ISOLATED REPRESSOR MOLECULES A SINGLE E COLI ONLY HAS ABOUT 5 - 10 MOLECULES OF LAC REPRESSOR

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

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

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

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

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

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 DIFFERENT SPLICING EVENTS OCCUR DURING DIFFERENT STAGES OF DEVELOPMENT OR IN DIFFERENT TISSUES