Question

Propose a metabolic reaction which would illustrate a positive feedback mechanism. Be sure to address the relationship between molecules in the reaction (substrate, product, enzyme, etc) and how the reaction would be both perpetuated, and eventually terminated.

Answer 1

Positive feedback enhances the change/ reaction brought by stimuli that amplify the reaction rate at much faster rate.It pushes the organism out of homeostasis sometimes needed for the survival. The response to a stimulus does not cease or reverse it instead it kepps going with the sequence. Many be therefore it is less common in nature than the negative one. It is harmful as in case like fever that causes metabolic changes pushing it to be higher but advantageous as in case of preotein digestion followed by formation of pepsinogen that is converted to pepsin. Pepsinogen is the substrate and pepsin is the product catalysed by acidic environment HCL of stomach. Pepsin conversion triggers pepsinogen to produce more pepsin, The resultant product amplify the substrate conversion rate in presence of the enzyme to produce more product. Stomach accumulates enough pepsin to be able to digest proteins. More examples of positive feedback are childbirth. ovulation, coagulation, platelet aggregation, inflammation and shock. In many instances positive feedback mechanisms rely on an external brake to terminate them.