Question

1. Discuss another important function of the electrochemical proton gradient that is indirectly related to ATP production.

2. Explain what an uncoupling agent is and describe how uncoupling agents dissipate the proton motive force

3. Discuss the reasons why naturally-occurring uncoupling proteins, which are especially abundant in brown adipose tissue of mammals, can be used as a source of heat production during exposure to cold temperatures.

Answer 1

Q1)Electrochemical proton gradient is a difference hydrogen ion concentration across a membrane producing a concentration gradient and an electrical potential gradient. These gradients together store potential energy in the cell which is available for work. Diffusion from an area of high hydrogen concentration to an area of lower hydrogen concentration does not require energy. Cellular respiration is dependent on the existence of an electrochemical proton gradient across the inner mitochondrial membrane.

During oxidative phosphorylation a high energy electron is passed along an electron transport chain the inner mitochondrial membrane in eukaryotes. This linked set of proteins carry out redox reactions which release energy. The energy released by electrons flowing through this transport chain, pumps hydrogen out of the matrix space across the inner mitochondrial membrane. This produces an electrical potential across the membrane and a store of potential energy as a pH gradient. The gradient created by this allows hydrogen back across the membrane, through an enzyme called ATP synthase. This process is called chemiosmosis and it occurs during cellular respiration. As this happens, the enzymatic activity of ATP synthase synthesizes adenosine triphosphate, ATP, from adenosine diphosphate, ADP in a phosphorylation reaction which is driven by the proton flow.

Q2)An uncopiling agent means a compound that dissociates electron transport from ATP synthesis and allows transport to proceed without synthesis.

Uncoupling proteins are membrane proteins, also embedded in the inner mitochondrial membrane, that passively transport protons, allowing them to bypass ATP synthase. Electron transport and hydrogen oxidation—and, upstream of it, degradation of energy-rich substrates—will continue, but ATP synthesis will cease; the energy that would have gone into ATP synthesis is simply dissipated as heat.

Uncoupling proteins are found in particularly high concentration in the mitochondria of brown fat tissue, which differs from the more abundant white fat tissue by its high density of mitochondria.Brown fat tissue serves the purpose of producing heat, by way of simply oxidizing fat without ATP production.