Lecture 15 Flashcards
What is enzyme induction and what are the two regulation types?
Bacteria exposed to different environments will only produce enzymes required for growth on a particular substrate in the presence of the specific molecule, this is due to selection for efficient systems and is known as enzyme induction. This can occur via negative regulation (gene expression turned off by regulatory protein known as repressor, if inactivated constitutive(constant) expression) or positive regulation (gene expression is turned on by a regulatory protein known as an activator, if inactivated no expression occurs). These will be activated by effector molecules typically related to or that are the substance.
How does lac operon regulation occur?
The lac operon is regulated by laci the repressor, this is converted into mRNA and binds to the operon in order to prevent transcription unless lactose is present to induce the laci to unbind to the operon. The lactose can get in due to the permease enzyme (part of lac operon) being quite stable and lasting a long time in the cell.
How was LacI found to be a repressor and what did they think this meant?
LacI was found to be a repressor due to mutations in it which were constitutive for production of enzymes. This originally led to it being believed to make an internal inducer whch would mean I- would be dominant over I+, this wasn’t the case. LacI+ is trans-dominant over LacI-
What is LacIs?
LacIs is dominant and cannot bind inducer, these mutants did not express lacZ, lacY or lacA and was mapped to a lacI gene. The IS repressor cannot bind inducer and hence permanently represses.
What are Oc mutants for the lac gene?
OC mutants cannot be bound to by LacI and hence are constitutively switched on. These mutations are rare as the OC region is quite small. These mutations are cis-acting meaning they only work on the genes directly linked to them.
