Chapter 25. Metabolism and Nutrition The food we eat is our only source of energy for performing biological work.
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The food we eat is our only source of energy for performing biological work.
There are three major metabolic destinations for the principle nutrients. They will be used for energy for active processes, synthesized into structural or functional molecules, or synthesized as fat or glycogen for later use as energy.
Glucose can be used to form amino acids, which then can be incorporated into proteins.
Excess glucose can be stored by the liver and skeletal muscles as glycogen, a process called glycogenesis.
If glycogen storage areas are filled up, liver cells and fat cells can convert glucose to glycerol and fatty acids that can be used for synthesis of triglycerides (neutral fats) in the process of lipogenesis.
The large amount of chemical potential energy stored in intermediate substances derived from pyruvic acid is released step by step.
The Krebs cycle involves decarboxylations and oxidations and reductions of various organic acids.
For every two molecules of acetyl CoA that enter the Krebs cycle, 6 NADH, 6 H+, and 2 FADH2 are produced by oxidation-reduction reactions, and two molecules of ATP are generated by substrate-level phosphorylation (Figure 25.6).
The energy originally in glucose and then pyruvic acid is primarily in the reduced coenzymes NADH + H+ and FADH2.