The nicotinic receptor for ACh is an example of a ligand-gated ion channel

TLS Online TPP Program

#Id: 2338

#Unit 3. Fundamental Processes

In E. coli, rRNA synthesis from the seven rRNA operons responds to cellular growth rate and to changes in the availability of crucial nutrients, particularly amino acids. The regulation coordinated with amino acid concentrations is known as the stringent response.

TLS Online TPP Program

#Id: 2339

#Unit 3. Fundamental Processes

Amino acid starvation leads to the binding of uncharged tRNAs to the ribosomal A site; this triggers a sequence of events that begins with the binding of an enzyme called stringent factor (RelA protein) to the ribosome. 

TLS Online TPP Program

#Id: 2340

#Unit 3. Fundamental Processes

When bound to the ribosome, stringent factor catalyzes formation of the unusual nucleotide guanosine tetraphosphate (ppGpp); it adds pyrophosphate to the 3 position of GTP, in the reaction.

TLS Online TPP Program

#Id: 2341

#Unit 3. Fundamental Processes

Bacterial promoters

TLS Online TPP Program

#Id: 2342

#Unit 3. Fundamental Processes

The consensus sequence reflects preferred –10 and –35 regions, separated by the optimum spacing (17 bp).

TLS Online TPP Program

#Id: 2343

#Unit 3. Fundamental Processes

Promoters with sequences closer to the consensus are generally “stronger” than those that match less well