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.
Enzymes. Enzymes are proteins, produced by living cells; they catalyze chemical reactions by lowering the activation energy. Activation energy is the energy required for a chemical reaction to occur. Enzymes are generally globular proteins with characteristic three-dimensional shapes.The active site is the binding site for the enzymeâs substrate. Enzymes are specific for substrate molecules.ctivation energy is the energy required for a chemical reaction to occur. Enzymes are generally globular proteins with characteristic three-dimensional shapes. The active site is the binding site for the enzymeâs substrate. Enzymes are specific for substrate molecules.