Regulation Of Gene Expression Flashcards
Gene Expression
Turning on the expression of a protein or building of proteins
Why is being able to turn off gene expression useful for a cell
So I can stop the production of that protein and save energy
Production of a protein
Done after transcription and translation
Constitutively expressed genes
Are always expressed
The protein is critical for the function of the cell and if it stops being expressed this so I will probably die
Ex enzymes essential to metabolism
Adaptively expressed genes
Genes used in different situations, expressed only one advantage to the cell
Induction: Turning on the transcription of a gene
Repression: turning off the transcription of a gene
Constitutively and adaptively expressed genes
Are all controlled at the genetic level by operons.
Ex: lac operon & trp operon
Induction gene (inducible)
(Adaptive)
Example: light sensor that turns on when you walk into a room.
Repression gene
(Adaptive)
Always on unless market is gone Factory always making something. Always selling, market goes away and turns off factory.
Why is the bacterial regulation of gene expression largely at the pre-transcriptional level?
Because There is no physical separation between the messenger RNA and the ribosomes there’s no way to keep them apart so in messenger RNA is produced the ribosomes grab the mRNA and start to turn it into a pro Tien immediately and because it can’t stop the ribosome from doing its job the only way to bacterial cell can regulate is by not making any messenger RNA and control things going on at the transcriptional level.
*only way to control is by stopping the form of mRNA by Turing on or off the expression. (RNA polymerase)
The only enzyme that does transcription
Creates RNA
RNA polymerase
(Reads along the template strand of DNA uses the info to form complementary RNA strand, which becomes the messenger RNA that goes to the ribosome )
Structure of an operon
Promoter RNA polymerase Repressor protein Operator Structural gene
Operon
Set of genes and the elements that control their expression
Promoter
Where RNA polymerase binds/starts process of transcription by recognizing the the template strand.
RNA polymerase (rna pol)
Makes mRNA from structural genes
Repressor protein
When active, prevents rna polymerase from moving along dna. Sits on operator
Operator
Where repressor binds (sequence of DNA)
Structural genes (dna)
Encode for proteins whose expression is regulated by the operon
Enzymes used for something
What is the lac operon involved in
The expression of enzymes that can break down the sugar lactose
Main enzyme in breaking down lactose
Beta galactosidase (gene 6)
Digests lactose( disaccharide ) into glucose and galactose (monosaccharides)
The Lac operon
Inducible gene expression
(Adaptive gene)
Turns on B gal enzyme when lactose is present by sticking to the repressor
Letting rna polymerase to produce mRNA
Digesting the lactose
If operator and repressor don’t exist
Then nothing can stop rna polymerase from working
When looking at an operon your going to see the same overall structure
Promoter, operator and structural genes
Simplified version
Terminator
Where RNA polymerase stops
The lac repressor protein
Is expressed continuously for operon to function. With its own promoter and repressor protein gene (lack) no operator present, so no way to stop expression.
The constant expression of a gene is
Constitutive expression (no operator)
It is the characteristic of these repressor proteins.
Constitutive Promoter, repressor protein, terminator. /adaptive Then another promoter, operator, structural genes, terminator
What substance induces the expression of beta galactose
Lactose
Suppose there was a mutation in the operator that caused it to no longer bind to the repressor pro Tien will gene expression be on or off?
Constantly on
Becomes constitutive
Will be making beta galactosidase over and over until it works itself to death
Suppose there it was a mutation and better galactosidase enzyme that caused it to be catalytically inactive. Well this operon work as intended
When lactose is in the cell: expression is on, makes enzyme but it’s broken and can’t digest lactose. Cell eventually dies.
If we change the repressor proteins so that it no longer binds to lactose will we ever be able to express Beta galactosidase
No it will always be stuck to operator, expression will always be off.
Repressible protein vs inducible protein
Both adaptive.
Only difference is the behavior of the repressor protein
Repressible gene expression operon example
Trp operon
Operon that makes the amino acid tryptophan
Usually in the on position
Negative feedback ( too much trp from outside enzymes are not made)
Is the TRPR Gene inducible or constitutively expressed
Constitutive because there is no operator
Trpr is the gene that creates the repressor protein for trp operon
Repressor protein is always expressed because there is no operator
Bacterial cells
Bacterial gene regulation
This is what happens in bacterial cells as the only form not really as used to be able to control the expressions of protein mainly because the expression of mRNA and the creation of protein happens essentially at the same time there is no separation between messenger RNA and a protein so the only way bacteria Sask have to stop expression of a protein is to throw up a roadblock in the front of RNA polymerase and the roadblock will stop that expression of that material.
