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Understanding Glycolysis

Glycolysis, which literally means “splitting sugar”, is a series of nine reactions that partially oxidize glucose and harvest two molecules of ATP. Figure 4.1 shows all nine of the reactions, but it is not necessary to attempt to memorize them all in this context. We are most interested in understanding the major events and the ultimate products of glycolysis.
Glycolysis occurs in the cytoplasm of animal cells, and it is important to remember three major aspects of the process: 
  • Glucose, a six-carbon compound, is ultimately broken down into 2 molecules of pyruvic acid, a three-carbon compound.
  • Two molecules of ATP are produced when glycolysis is complete.
  • Two molecules of the coenzyme NAD+ (nicotinamide adenine dinucleotide)  are reduced to NADH when glycolysis is complete.
A few comments may be helpful at this point.
  • Glycolysis is the first step in glucose metabolism in all vertebrates and almost all living cells.
  • The ATP made during the process is generated by substrate level phosphorylation, which simply means a phosphate group attaches to ADP directly from one of the reactants in the pathway to make ATP.
  • NAD+ is a common coenzyme (see Chapter 3) that acts as an electron shuttle. It contains more potential energy when it is reduced to NADH than in its oxidized form, so the generation of NADH represents the temporary storage of energy.

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