Prokaryotic Gene Regulation Flashcards
If all cells have the same genes, how do they have different functions?
It depends of how the genes are expressed and regulated
What is an operon? Do both prokaryotes and eukaryotes have operons?
A unit made up of linked genes which is thought to regulate other genes responsible for protein synthesis -exist in both eukaryotes and prokaryotes but primarily found in prokaryotes
How many mRNAs are produced from one operon?
One mRNA strand is produced and multiple polypeptide subunits
What is a promoter and what is an operator?
The promoter is the sequence where the RNA polymerase binds and begins transcription - an operator is a regulatory sequence that a repressor can bind to
What is produced by the trpR gene? What is the function of this protein?
The repressor protein is encoded by a gene called trpR - it codes for the tryptophan repressor protein itself
Repressible system
What is the function of the overall genes in the trp operon?
5 genes in this operon
Biosynthetic pathway to make tryptophan
What binds to the promoter of the trp operon? What binds to the operator?
The repressor binds to the DNA of the operator
RNA polymerase attaches to the promoter
What molecule binds to the TrpR protein? Is the TrpR molecule functions with or without this molecule? Does its binding activate or inactivate the TrpR protein?
Trp binds to the TrpR protein - that makes it active - protein isn’t active and able to bind without it
If tryptophan is present, are the trp genes expressed? Is an mRNA produced? Are proteins produced?
The trp operon is repressible - the effector molecules interact with the repressor protein such that it can bind to the operator
If tryptophan is present then there is no need to create any more and so the repressor is active and the operon is switched off- as tryptophan accumulates it inhibits its own productivity by activating the repressor, which binds to the operator blocking transcription
What happens when tryptophan is absent?
It has to make tryptophan and so the repressor is inactive and the operon is on- RNA polymerase attaches to the DNA at the promoter and transcribes the operon’s genes
If a mutation in the promoter completely disrupts the RNA polymerase binding site are the genes in the trp operon transcribed, translated, both or neither?
Neither
If a mutation critically disrupts the operator sequence of the trp promoter, but RNA polymerase can still bind, are the genes in the trp operon expressed in the presence and absence of tryptophan?
Yes
If a mutation disrupts a critical codon in the trpE gene, is it transcribed, translated and is tryptophan produced? If a mutation disrupts a critical codon in the trpR gene are the genes in the trp operon expressed?
Yes
