Regulation of gene expression : operons, promoters, and Transcription control

What are the levels of gene control in bacteria?

Transcriptional control, mRNA processing, post-transcriptional modification, and gene deletion.

Which mechanism of gene regulation is best for conservation of resources?

Transcription

What do promoters contain?

Instructions about when to turn genes on and off.

What are the two categories of DNA-binding proteins?

Repressors and Activators.

How do DNA-binding proteins interact with DNA?

By forming hydrogen bonds with DNA bases.

What are consensus sequences in prokaryotic promoters?

Sequences recognized by the σ subunit of RNA polymerase, such as the Pribnow box (-10) and TTGACA (-35).

What is an operon?

A cluster of genes under the control of a single promoter.

What is an inducible operon?

An operon that is stimulated to express genes in the presence of a particular substance, like the lactose operon.

What is a repressible operon?

An operon that is turned off in the presence of a particular substance, such as the tryptophan operon.

What does the lactose operon encode?

Enzymes required for the utilization of lactose.

What happens to the lactose operon when lactose is absent?

The repressor protein binds to the operator, blocking transcription initiation.

What is polycistronic mRNA?

mRNA that carries multiple open reading frames (ORFs), each translated into a polypeptide.

Which enzyme does β-galactosidase not convert lactose into?

Maltose.

What is the role of the lacI gene?

It codes for a repressor that affects the production of permease and β-galactosidase.

What is the effect of the lacI+ allele?

It is trans dominant over lacI- and acts on both DNA molecules.

What is the role of the lacO gene?

It is cis acting and only affects genes on the same DNA molecule.

What does the lacIs gene encode?

A super-repressor that does not bind lactose.

What is the function of the catabolite activator protein (CAP)?

It binds to a special site near the promoter to turn on transcription when glucose is absent.

What is the role of tryptophan in the regulation of the trp operon?

It binds to the repressor protein, enabling it to block transcription.

What is negative control in the context of repressible operons?

The repressor protein binds to the operator and inhibits transcription.

What is attenuation in the regulation of the trp operon?

It involves the folding of the leader region of mRNA into secondary structures that affect transcription.

What are the four regions of the 5' UTR in the trp mRNA?

Regions that fold into two distinct secondary structures, with complementary base pairing.

What is the primary function of the enzymes encoded by the trp operon?

Involved in the biosynthesis of tryptophan.

What happens to the operon when glucose is low?

CAP binds to the promoter, facilitating RNA polymerase binding and transcription.

What is the result of a mutation in the operator gene (Oc)?

Transcription can still occur from the other DNA molecule.

What is the significance of the Pribnow box?

It is a consensus sequence located at -10 that is crucial for transcription initiation.

What is the relationship between the repressor and the operator in the presence of lactose?

The repressor does not bind to the operator, allowing transcription to occur.

What is the role of the RNA polymerase in transcription?

It synthesizes RNA from the DNA template.