You might see the word alloy described as a mixture of metals, but that's a little bit misleading because some alloys contain only one metal and it's mixed in with other substances that are nonmetals (cast iron, for example, is an alloy made of just one metal, iron, mixed with one nonmetal, carbon).
Energy substrates in the human body are either carbohydrates, fat or proteins. Protein degradation yields amino acid residues which can be converted to carbohydrates and used in energy production. Carbohydrates (sugars) and amino acids from proteins give approximately 4 kcal/gram dry weight when burned in the body.
substrate. any substance upon which an enzyme acts. substrate binding site. part of the active site of an enzyme which includes the amino acid residues that come into contact with the substrate. substrate specificity. range of substrates that can be catalytically converted to product by an enzyme.