BISC 202 Gene regulation and lac operon (W12-13)

key ideas about gene expression

what is gene regulation about?

how we express a gene or not

how we make a protein or not

why is it important to study gene regulation?

D. All of the above

operon

a cluster of structural genes that are co-ordinately regulated by a single promoter region

the lac operon

what happens to structural genes during transcription and translation

repressor

when is the lac operon expressed?

when is the lac operon not expressed?

no lactose present

non-induced lac operon

lactose present

inducer

An inducer is a molecule that induces the expression of an operon. Lactose is a classic example.

how does an inducer work?

Inducers are a type of allosteric effector. They bind to an allosteric site on a protein (like a repressor), which changes the protein's shape and affects its function

inducible system

A system where the expression of a gene can be turned on (induced) by adding a specific molecule, such as an inducer. This usually involves the inducer preventing a repressor from blocking transcription.

negative regulation

in negative regulation, binding of the regulatory molecule decreases transcription

positive regulation

in positive regulation, binding of the regulatory molecule increases transcription

transcriptional regulation

The process of controlling gene expression by regulating the transcription of genes, which is the first step in creating a protein from a gene.

what must bacterial cells need to be able to do?

regulatory proteins binding sites

what is helpful when studying the regulation of a gene/operon?

what is merodiploid?

a bacterium that is partially diploid (it carries a 2nd copy of a part of its genome)

how do you make a merodiploid strain?

trans-acting vs cis-acting

gene regulation/lac operon key concepts

what effect should the absence of glucose have on lac operons when lactose is present?

lac operon expression should be promoted, with an activator

what happens when there is not enough glucose?

cells need more lac enzymes to use the available lactose as a carbon and energy source instead

what happens when glucose is abundant?

there is much less expression of the lac operon

ultimate

digesting lactose takes more time/energy than digesting glucose

proximate

the activator protein is not bound to the lac operon

activators and repressors

D. the repressor stops blocking expression of the lac operon

the lac activator and its effector

the lac activator and its effector when there’s not enough glucose

the lac activator and its effector when there’s lots of glucose

A. no expression

B. Very little expression

ara operon

ara operon vs lac operon

repression of the ara operon vs lac operon

activation of the ara operon vs lac operon

why does it make sense that both the ara operon and lac operon use CAP and cAMP for positive regulation?

why does the AraC protein remain attached to aral?

coordinated control of gene expression with operons

regulation of operons for synthesizing nutrients

what are the two mechanisms for regulation of the trp operon?

repression and attenuation

regulation of the trp operon with repression

regulation of the trp operon with attenuation

what kind of control is the trp repressor an example of?

a repressible system (something in the environment can repress gene expression)

E. constitutive transcription of the trp operon

how does termination mechanism of transcription relate to trp operons?

how do ribosomes disrupt the hairpin loop when [trp] low?

what happens when [trp] is high?

what happens when [trp] is low?

what is the overall effect of the two regulatory mechanisms?

does attenuation happen in other amino acid pathways?