Explain how a cell degrades and extracts energy from compounds other than glucose, including fats and proteins.
In addition to carbohydrates, fats and proteins can also be broken down to release energy. Fats are first hydrolyzed into glycerol and fatty acids. The glycerol, a three-carbon compound, is then fed into the glycolytic pathway at the point where G3P appears. The fatty acids are broken into two-carbon fragments, converted into molecules of acetyl-CoA, and fed into the Krebs cycle. Similarly, proteins are first hydrolyzed into their constituent amino acids. Next, some amino acids are converted into pyruvic acid, some into acetyl-CoA, and some into compounds of the Krebs cycle. Whereas equal amounts of carbohydrate and protein yield about equal amounts of energy, an equal amount of fat will yield about twice as much energy since fats are more completely reduced to begin with.
