Question

‘Bacterial chemotaxis is controlled by a two-component sensory system’. Discuss. In your answer place emphasis on the roles of receptors, kinases, and adaptation enzymes in the signal transduction process.

Answer 1

Ans . Two component systems serve as a basic stimulus-response coupling mechanism to allow organisms to sense and respond to changes in many different environmental conditions. They typically consists of a membrane bound histidine kinase that senses a specific environmental stimulus and a corresponding response regulator that mediates the cellular response, mostly through differential expression of target genes.

Signal transduction occurs through the transfer of phosphoryl groups from ATP to a specific histidine residue in the histidine kinases. This is an autophosphorylation reaction.Subsequently the histidine kinase catalyze the transfer of phosphate group on phosphorylated histidine residues to an aspartic acid residueon the response regulator.

Phosphorylation causes the response regulator's conformation to change, usually activating an attached output domain , which then leads to stimulation (or repression ) of expression of target genes. The level of phosphorylation of the response regulator controls its activity.

Two-component signal transduction enable bacteria to sense, respond and adapt to a wide range of environments, stressors and growth conditions.

Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecule creating a response.