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
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

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
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

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
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?

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
IF YOU HAVE CHICKEN MAC NUGGETS AND A MILKSHAKE YOUR ECOLI WILL BE VERY HAPPY
SCARF UP ALL THE AA IN TRYTOPHAN
LETS LOOK AT HOW THEY DO THAT

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
HOW DOES IT CONTROL WHEN TO DO THIS?
HOW DOES IT NOT DO THIS IF TRYPTOPHAN IS PRESENT IN THE MEDIA
IT WOULD BE A WASTE TO DO IT THEN

6. Fig. 16.6 WHEN THE ENVIRONMENT LACKS TRYP
THERE IS NOTHING TO ACTIVATE THE REPRESSOR
SO RNA POLYMERASE BINDS TO THE PROMOTER REGION AND MAKES TRP
WHEN TRYPTOPHAN IS PRESENT IN THE ENVIRONMENT
IT BINDS TO THE REPRESSOR WHICH IS THEN ACTIVATED
AND CAN BIND TO THE OPERATOR REGION AND BLOCK
THE TRANSCRIPTION OF THE TRP GENES

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
LIKE THE TRYP GENE CODES FOR THE SYNTHESIS OF TRYPTOPHAN

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
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

13. 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

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

15. 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

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
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 MOLECULES OF LAC REPRESSOR

18. LAC OPERON REGULATED SYNTHESIS OF INDUCIBLE ENZYMES

19. 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

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

26. A EUKARYOTIC GENE AND ITS TRANSCRIP
POST TRANSCIRPTIONAL CONTROL

27. OPPORTUNITIES FOR THE CONTROL OF GENE EXPRESSION IN EUKARYOTIC CELLS