Biochemistry of the Kreb's Cycle

Mitochondria are found in nearly every cell in the human body.  These structures are described as the powerhouse of the cell because they generate most of the cell's supply of adenosine triphosphate or commonly known as ATP, which is used as a source of chemical energy.  So the question of which form of biochemistry yields more energy in the Kreb's Cycle, Beta Oxidation via fats or Glycolysis via glucose from carbs.  Lets take a look.....

  • Glycolysis breaks down glucose molecules into two molecules of pyruvate in 10 enzymatically mediated reactions.
  • Glycolysis occurs in the cytosol and its product, pyruvate, is imported into the mitochondria.
  • Glycolysis produces a net gain of 2 NADH and 2 ATP
  • Pyruvate is transformed into Acetyl CoA inside the mitochondria, yielding one more NADH.
  • Fatty Acids are activated in the cytosol, and transported inside the mitochondria for oxidation.
  • One round of oxidation of a fatty acid yields one molecule of Acetyl CoA, one NADH and one FADH2
  • Fatty Acid Oxidation is a 4 step process involving two oxidation steps, a hydration and a thiolysis, all of which are enzymatically mediated.
  • Acetyl CoA is the substrate for the TCA cycle.
  • The Citric Acid Cycle is an eight step enzymatically mediated process.
  • For each round of the TCA cycle, 3 NADH, 1 FADH2 and 1 GTP are produced.
  • Fatty acids, because of their long reduced carbon chains, are able to power many more cycles of the citric acid cycle than Glucose, on a per carbon basis.

On a per molecule basis, it becomes clear that Ketones or fats are a much better source of energy to make ATP than are glucose molecules.  Fat molecules are arranged in triglycerides–fully reduced molecule with three fatty acid chains, each of which may contain 18 carbons.  Thus a single triglyceride has the potential to drive (18/2)x3=27 rounds of the citric acid cycle, as compared to 2 per molecule of glucose.  Therefore Beta Oxidation is far more efficient than Glycolysis.  The more efficient we produce energy the less oxidative stress produced or free radicals which cause inflammation.  The faster we recover with less tissue damage.  

This information came from Alberts’ Molecular Biology and the Cell.