Question

Define, describe, and explain the importance of low versus high energy charge. Why can’t a cell just make as much ATP as it wants and keep the ATP on hand until it is needed?

Answer 1

The adenylate energy charge is an index used to measure the energy status of biological cells. ATP or Mg-ATP is the principal molecule for storing and transferring energy in the cell : it is used for biosynthetic pathways, maintenance of transmembrane gradients, movement, cell division, etc.

The energy charge of most cells varies between 0.7 and 0.95 - oscillations in this range are quite frequent. When the energy charge increases from 0.6 to 1.0, the citrate lyase and phosphoribosyl pyrophosphate synthetase, two enzymes controlling anabolic (ATP-demanding) pathways are activated, while the phosphofructokinase and the pyruvate dehydrogenase, two enzymes controlling amphibolic pathways (supplying ATP as well as important biosynthetic intermediates) are inhibited.

ATP is a negative regulator of PFK, which makes sense: if there is already plenty of ATP in the cell, glycolysis does not need to make more.The body only stores a very small quantity of ATP within its muscles cells, enough to fuel only a few seconds of exercise. Because of this the body must constantly synthesise new ATP in order to constantly fuel movement.