Suppose you are stranded on a deserted island and have nothing but protein to

-   The protein will first be broken down into amino acids by digestive proteases and the amino group will be removed. The body will synthesize the proteins needed and other N-containing compounds.

-   To use amino acids as an energy source, a process called deamination first strips off the amino group (–NH2), leaving a carbon skeleton. The carbon skeleton is then used to pro-duce energy, glucose, fatty acids, and ketone bodies. The structure of the carbon skeleton and the number of carbon atoms determines its fate. Some become pyruvate (will undergo gluconeogenesis), acetyl-Coa (citric acid cycle for ATP), acetoacetyl-CoA, or one of the in-termediates of the TCA cycle (oxaloacetate). The complete breakdown of alanine, for ex-ample produces 12.5 ATP, while methionine produces 5 ATP. Also recall that the pro-duction of ketone bodies regenerates coenzyme A which is required for ?-oxidation to pro-duce energy from fatty acids.

-   The proteins consumed can also be converted into fumerate, succinyl-CoA, and ?-ketoglutarate, all of which can undergo the glucogenic pathway to produce ATP.

-   Since the person’s diet in this example does not contain carbohydrates, blood glucose level will decrease, risking the acidic effects of high levels of ketone bodies. To prevent this, gluconeogenesis will take place (the metabolic pathway that results in the generation of glucose).