Ex2- Regulation of Gene Expression Flashcards
What is Gene Expression?
The process by which the expression of genes is turned on and off at different times and under different conditions.
True or false? Microorganisms are able to control how much of each building block it makes.
True
True or false? Since biosynthesis of building blocks involves a series of enzymic reactions, the cells either turn on or off the enzyme synthesis or enzymic activity.
True
What is the most common/ easiest way to regulate gene expression? Furthermore, how is this able to control gene expression?
The most common way to regulate gene expression is through Transcription. This occurs because transcription regulator proteins bind to DNA through Helix-turn-Helix motifs. This binding can act as either a positive or negative and in some instances even both.
How does the negative binding of the transcription regulator proteins occur?
The repressor protein binds to the operator and prevents the binding of RNA pol to the promoter and thus inhibiting protein synthesis.
How does the positive binding of the transcription regulator proteins occur?
The activator protein is required for the initiation byDNA pol onto the DNA strand by increasing its affinity to the promotor region and thus enhancing protein synthesis.
What is Posttranslational regulation?
Any regulation that occurs after the gene has already been transcribed into mRNA with the most common being translational regulation.
What is the significance of Joshua Elderberry’s work?
-had recognized and isolated a large number of lac- mutants.
• he had mapped the lac gene - quite accurately as it turned out.
-Developed procedures to isolate β-galactosidase and to measure its activity in vitro.
• Synthesized a number of different β-galactosides
o-nitro-phenyl-β-D-galactoside (ONPG)
What type of inducers are ß-galactosides? Also which is the most common in
Melvin Cohn identified ß-galactosides as inducers of enzyme activity but were not substrates for ß-galactosidase also known as Gratuitous inducers.
-with the most common being isopropyl-thio-ß-Dgalactsode (IPTG)
Can Enzymes adapt?
No the discovery of gratuitous inducers killed off any notion of enzyme adaptation and lead to a new concept known as induction.
What are the functions and names of the 3 loci responsible for lactose metabolism in E.coli?
- LacZ which coded for the ß-galactosidase;cleaves the lactose molecule to form glucose
- LacY which coded for the lactose premease;allowing lactose into the cell
- LacA which is coding for the transacetylase; unkown
What is the function of the lacI protein and hoe does this occur?
The function of the lacI protein is to act as a repressor protein . IN the absence of lactose binds to the lacO sequence located near the promoter and thus prevents the binding of the RNA polymerase blocking the transcription of the structural lac genes.
What happens when E.coli is in the presence of lactose?
In the presence of lactose the inducer (allolactose) binds to the repressor thus resulting in a conformational change that is no longer able to bind to the operator, and allowing RNA polymerase to bind to the lacP and transcribe the lacZ, lacY, and lacA genes.
What is the difference between a non inducible and constitutive mutation of the lac operon?
Non-inducible- mutations that seem to abolish expression of the genes.
Constitutive mutations are those that cause increased expression of the genes.
What is the most important characteristic in regards to the repressor protein of E.coli?
The most important property of the repressor is its characteristic pleiotropic specificity of action. Since the repressor is both highly specific and mutations of the I gene do not affect any other system, and it is pleiotropic since both the galactosidase and acetylase are affected simultaneously and quantitatively to the same extent, by such mutations.
True or False: Once the existence of a specific repressor is considered as established, the existence of an operator element is also established.
True ince the repressor is established the problem is not whether an operator exists, but where and how it intervenes in the system of information transfer.
What does it mean to say that the repressor protein is pleiotropic in the lac system?
It means that at the mutations in the lacI affect 3 unrelated genes
True or False?
The operator, its specific complimentarily configuration must be genetically determined; therefore it could not be affected by mutations which would alter or abolish its specific affinity for the repressor, without necessarily impairing its activity as initiator of information-transfer.
FALSE any mutation to the operator will cause the affinity of the operator to change and could thus lead to impairment or overexertion, and in other instances a complete loss of the RNA polymerase ability to transcribe the genes.
How are you able to isolate the lacl-mutant phenotype in E.coli?
The mutant alleles can be isolated by mutagenizing an F’ lac factor, transforming it into a lac deletion strain of E. coli, and then plating it on X-gal plates in the absence of any inducer. Once blue colonies appear it would inmate the expression of ß-galactosidase, and will display constitutive expression of the operon since there is no functional repressor present to block it.
How many bp in length is the LacZ gene and what does it code for in the lac operon?
The lacZ gene is 3072 bp in length and codes for ß-galactosidase the largest peptide formed by E.coli
How many bp in length is the LacY gene and what does it code for in the lac operon?
The lac Y gene is 1251bp in length and codes for the active form of the enzyme known as ß-galactsidase permease
How many bp in length is the LacA gene and what does it code for in the lac operon?
LacA is 609bp in length and codes for tiogalactoside transacetylase
How many regulatory genes does the lac operon contain and which gene codes for the repressor protein and lactose repressor?
The lac operon has only one regulatory gene: lacI which codes for the regulatory protein, the lactose repressor.
True or false: the lac operon contains two promoters although the second promoters function is not clear.
True
How is the lac operon regulated and how does this mechanism work?
The lac operon is regulated by catabolite repression. When the catabolite activator protein (CAP), and the effector protein cAMP bind to the CAP-binding site located 61.5bp ahead of the promoter this change allows the RNA polymerase bind more effectively and begin transcription.
True or False: Mutations in the lacZ or lacY genes results in a loss of both activities.
False mutations in the lacZ or LacY genes result in a loss of either (but not both) activities as both of these mutations are recessive.
True or False: A recessive mutation in a linked gene, lacI, resulted in high levels of the lacZ and lacY even in the absence of an inducer, this is said to be a regulatory mutation.
True this is said to be a regulatory mutation because the mutation governs the expression of the structural genes.
True or False: Dominant mutations in the LacI(lacI S) resulted in an induced phenotype for both the lacZ and LacY. which act in cis.
False the Dominant mutations in the lacI( = LacIS) resulted in a non-inducing phenotype for both lacZ and LacY. Which act in TRANS.
What are the two different kinds of elements present in the lac operon’s regulation?
The two elements that are present in the lac operons regulation are DNA binding sites and Proteins.
DNA binding sites include the LacP LacO and Pi sites. While the Proteins involves include: CAP, LacI, LacZ,LacA, and LacY.
How are you able to distinguish between DNA binding sites and mutant proteins?
Through the use of Pseudo-Diploid Genetics we are able to distinguish between a trans acting site ( protein) or a cis acting site (DNA binding site)
What is a Trans-acting site?
A trans-acting site is a diffusible protein that is able to act on another DNA sequence from afar.
What is a Cis-acting site?
A cis acting site is a DNA sequence that is not able to act from on another DNA sequence without being near another DNA site to function.
