# Energy Storage in Biological Systems

Living organisms use two major types of energy storage. Energy-rich molecules such as glycogen and triglycerides store energy in the form of covalent chemical bonds. Cells synthesize such molecules and store them for later release of the energy. The second major form of biological energy storage is electrochemical and takes the form of gradients of charged ions across cell membranes. This learning project allows participants to explore some of the details of energy storage molecules and biological energy storage that involves ion gradients across cell membranes.

## Energy storage molecules
### Examples of energy storage molecules

Glucose is a major energy storage molecule used to transport energy between different types of cells in the human body.
Starch

### Fats

Fat itself has high energy or calorific value and can be directly burned in a fire. In the human body and presumably other animals, it serves a number of roles as there are different kinds of fats, but for the purpose of the discussion here, fats are frequently found associated with each of the organs in the body.
For example, there is a deposit of fat on the heart and it was only relatively recently that it was realized that this acts as a temporary storage of buffer for energy. If one thinks of the blood system flowing around a heart, the glucose levels in it can fluctuate depending on a number of factors, such as whether one has recently digested a meal or engaged in strenuous activity. As with most machines, steady inputs cause less strain on the system than large fluctuations and the aforementioned cardiac fat assists in smoothing out during those lean periods and allows the heart to continue operating without additional strain.

### Adenosine triphosphate

Adenosine triphosphate or ATP is one of the key molecular energy carriers in the biological world.

## Chemiosmosis

The term chemiosmosis refers to the inter-conversion of chemical energy (energy in the form of chemical bonds) and energy in the from of a transmembrane electrochemical gradient. The idea of "chemiosmotic coupling" arose largely from the work of Peter D. Mitchell and revolutionized the way biologists think about energy storage in biological systems.

### ATP

Adenosine Triphosphate (ATP) is synthesized by the F0-F1 ATP Synthase Complex. ATP Synthase is situated with one side facing into the inner membrane space, using a proton gradient (chemiosmotic gradient) to initiate changes in conformation of the subunits of the complex by allowing protons to move through the complex and into the inner membrane space. The changes in conformation (From Loose to Tight to Open) facilitate the binding of ADP and a phosphate (to the Loose site), covalently bonding of the ADP and Phosphate to form ATP (Tight site) and release of the completed ATP molecule (Open site). Four protons must move through the complex to initiate change in conformation necessary for change between Loose, Tight and Open; That is, twelve protons moving through the complex makes one complete turn, and 3 ATP. See ATP Synthase.

### Transmembrane ion gradients
## Other uses for energy in transmembrane gradients

w:Action potential