23. Bacterial Gene Regulation 1 Flashcards
what is consitutive and regulated gene expression?
consitituive: gene is expressed through transcription and translation at all times
regulated: gene is expressed only when required. usually because of regulation of transcription
what is a promoter?
a site where RNA polymerase can bind to DNA and begin transcription
what is co-ordinated expression?
enzyme encoded by clustered genes show the same pattern of control - when one enzyme is produced, the others are too
what is a polycistronic mRNA? what type of cell is it in and why?
an mRNA molecule that contains the coding sequences of more than one gene. there are multiple ‘start’ and ‘stop’ codons to make multiple polypetides during translation.
only in prokaryotes because eukaryote mRNA do not include ribosome binding sequences. (shine-dalgarno)
what is a repressible operon?
the operator is positioned within the promoter or between the promoter and the enzyme coding genes. the ‘‘on off’ switch for making the prokaryote cell to make tryptophan itself (or another amino acid) because there is a lack of it in the enviornmnet. it controls the access of RNA polymerase to the genes. it acts as a barrier for transcription to make tryptophan (or another essential amino acid)
study image!
why is the trp operon classifed as a repressible operon?
becuase the default state is that gene expression for making trp is ON, so it must bind to the operator if trp is present to act as a repressant
what is the gene that regulates gene expression that encodes for a repressor protein? what does it do?
trpR (trp repressor) is a regulator protein which is capable of switch the trp operon off when trptophan has been taken in from the enviornment and has binded to the operator site.
study image!
what are the funcitons of the repressor
repressor: has the ability to bind to the operator if trp is bound to it (from being consumed) and stop RNA polymerase synthesising to make trp. or if no trp is bound from the enivonrment, the repressor protein cannot bind to the operator site in the trp operon.
what is a co-repressor and what molecule is it?
tryptophan is a co-repressor because it binds to the receptor protein, which then bind sto the operator to stop translation (kind of like the middle man to stop the process)
what is an inducible lac operon?
a different method of control - they are inducible (inactive by default) rather than repressible (active by default - the operon). the trascription of an inducible operon is stimulated when a specific molecule interacts with a regulatory protein
how does the inductible lac operon regulate in response to the availability of lactose and glucose?
all three enzymes (operon, promotor and operator) are synthesised in a process called induction in the prescene of lactose
