Genetics Notes – Thijs Rood
Chapter 14 - Gene regulation in bacteria
Gene regulation basics
- Gene regulation is the level of gene expression that can vary under different conditions
o Proteins are made only when required:
Metabolism
Response to Environment
Cell division
Development, cell fitness and other reasons
o In transcription: Regulatory proteins, transcriptional terminators (most common)
o In translation: Repressor proteins, Antisense RNA can bind to prevent
o Post translation: Covalent modifications, feedback inhibition
- Constitutive genes are always expressed and thus not regulated
o Often for proteins that are necessary for survival
In transcription regulatory proteins can bind to increase or decrease the transcription rate, these
proteins are called repressors and activators respectively. Effector molecules/ligands bind to these
(repressor/activator) and influence their effect. These are called inducers (+) and inhibitors (-).
Lac operon: involved in the catabolism of lactose
An operon is a regulatory element that consists of a few structural genes with one promoter and one
terminator. Thus we have a promoter -> operon (cis) -> terminator -> structural genes.
- Lacl gene: encodes for a repressor, this repressor is inducible by allolactose (trans)
- CAP: catabolite repression (diauxic growth): if glucose is available it is used first.
o Glucose present > adenylyl cyclase is inhibited > decrease cAMP > cAMP cannot bind
to CAP > Lac transcription decreases
- Make a partial diploid merozygote to study mutations and trans/cis effects.
Trp operon: involved in the anabolism of the amino acid tryptophan
- High trptophan levels induce a repressor
- Stem loops also influence this operon:
o 1-2, 3-4 stem loop: no translation
o 2-3 stem loop: slow translation
o 3-4 stem loop: fast translation
, Translational regulation
Can be done with repressors:
1. Binding next to the Shine-Dalgarno sequence/start codon will hinder the ribosome
2. Binding outside the Shine-Dalgarno: stabilise a secondary mRNA structure that hinders
Or can be done with antisense RNA: the protein ompF can be inhibited by micF regulating osmolarity
Posttranslational regulation
Feedback inhibition: if a final product of an enzyme cycle becomes too high it inhibits the first
enzyme and less intermediate products are made
Covalent modification: Phosphorylation (–PO4), Acetylation (–COCH3), Methylation (–CH3)
Riboswitches: transcription and translation modification
The binding of a small molecule may alter the form of a stem loop either activating of deactivating it.
Chapter 14 - Gene regulation in bacteria
Gene regulation basics
- Gene regulation is the level of gene expression that can vary under different conditions
o Proteins are made only when required:
Metabolism
Response to Environment
Cell division
Development, cell fitness and other reasons
o In transcription: Regulatory proteins, transcriptional terminators (most common)
o In translation: Repressor proteins, Antisense RNA can bind to prevent
o Post translation: Covalent modifications, feedback inhibition
- Constitutive genes are always expressed and thus not regulated
o Often for proteins that are necessary for survival
In transcription regulatory proteins can bind to increase or decrease the transcription rate, these
proteins are called repressors and activators respectively. Effector molecules/ligands bind to these
(repressor/activator) and influence their effect. These are called inducers (+) and inhibitors (-).
Lac operon: involved in the catabolism of lactose
An operon is a regulatory element that consists of a few structural genes with one promoter and one
terminator. Thus we have a promoter -> operon (cis) -> terminator -> structural genes.
- Lacl gene: encodes for a repressor, this repressor is inducible by allolactose (trans)
- CAP: catabolite repression (diauxic growth): if glucose is available it is used first.
o Glucose present > adenylyl cyclase is inhibited > decrease cAMP > cAMP cannot bind
to CAP > Lac transcription decreases
- Make a partial diploid merozygote to study mutations and trans/cis effects.
Trp operon: involved in the anabolism of the amino acid tryptophan
- High trptophan levels induce a repressor
- Stem loops also influence this operon:
o 1-2, 3-4 stem loop: no translation
o 2-3 stem loop: slow translation
o 3-4 stem loop: fast translation
, Translational regulation
Can be done with repressors:
1. Binding next to the Shine-Dalgarno sequence/start codon will hinder the ribosome
2. Binding outside the Shine-Dalgarno: stabilise a secondary mRNA structure that hinders
Or can be done with antisense RNA: the protein ompF can be inhibited by micF regulating osmolarity
Posttranslational regulation
Feedback inhibition: if a final product of an enzyme cycle becomes too high it inhibits the first
enzyme and less intermediate products are made
Covalent modification: Phosphorylation (–PO4), Acetylation (–COCH3), Methylation (–CH3)
Riboswitches: transcription and translation modification
The binding of a small molecule may alter the form of a stem loop either activating of deactivating it.
