Fundamentals of Molecular Biology. Part 1: Molecular Cell Biology - A.N. Ogurtsov 2011

Oxidation of glucose and fatty acids
Glycolysis

Complete aerobic oxidation of a single glucose molecule yields 6 molecules of СО₂ and is accompanied by the synthesis of 30 ATP molecules

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The First stage of glucose METABOLISM—GLYCOLYSIS—takes place in the Cytosol and does not require molecular oxygen. As a result of glycolysis, one glucose molecule yields two ATP molecules and two molecules of the three-carbon compound Pyruvate (pyruvic acid). In aerobic Cells, this pyruvate is transported into the Cell/35.html">Mitochondria, where it is oxidized by molecular oxygen to СО₂.

Through Chemiosmotic Coupling, the Oxidation of Pyruvate drives the Synthesis of the vast majority (out of 30) of ATP molecules produced during glucose metabolism.

First, we will examine the biochemical processes involved in the Oxidation of glucose and Fatty acids to СО₂ and Н₂О, and then we will look closely at the mechanisms of electronic relaxation.

Glycolysis is carried out by ten Water-soluble cytosolic Enzymes, which convert a single glucose molecule into two pyruvate molecules (Figure 150).

Figure 150 - Pathway of glycolytic reactions

All intermediates between glucose and pyruvate are phosphorylated compounds. Reactions 1, 3, and 10 (shown in Figure 150) are irreversible under physiological conditions.

Glycolysis generates four ATP molecules via enzymatic reactions 7 and 10, while consuming two ATP molecules in reactions 1 and 3. Consequently, the glycolysis of a single glucose molecule yields a net total of only two ATP molecules.

Enzymatic reactions 7 and 10 (Figure 150)—unlike the ATP Synthesis in Mitochondria and Chloroplasts, which relies on a proton-motive force—proceed via so-called "substrate-level phosphorylation".

Substrate-level phosphorylation refers to The transfer of inorganic phosphate Р_i to ADP (or GDP) driven by a high chemical potential (rather than Oxidative Phosphorylation, which utilizes an electrochemical gradient across a biological membrane). These processes are termed substrate-level phosphorylation precisely because they are integral parts of a metabolic pathway ("substrate chain").

To properly balance the glycolytic reaction, four additional hydrogen atoms (specifically, four protons and four electrons) must be accounted for on the right side of the equation

All four electrons and two of the four protons are transferred to two molecules of the electron carrier nicotinamide adenine dinucleotide in its oxidized form, NAD⊕, converting them to their reduced form, NADH (Figure 151)

Reaction 6 in Figure 150, which generates these hydrogen atoms and transfers them to NAD⊕, is catalyzed by the enzyme glyceraldehyde-3-phosphate dehydrogenase.

Figure 151 - Diagram of nicotinamide adenine dinucleotide oxidation: a - oxidized form NAD⊕; b - reduced form NADH