Strategy of Glycolysis

Strategy of glycolysis

> 1. The process of glycolysis requires ATP energy input before ATP and NADH energy can be released. This breaks glycolysis into two phases - an energy input phase (reactions 1-5) and an energy release phase (reactions 6-10). The energy input phase includes two reactions (hexokinase and phosphofructokinase), each where ATP is used. These two steps are bypassed in gluconeogenesis by different enzymes which simply hydrolzye the phosphate group added by phosphorylation in glycolysis. The third place where glycolysis and gluconeogenesis differ is the pyruvate kinase step (the last reaction in glycolysis). This step is bypassed in gluconeogenesis because it is highly unfavorable energetically.

> 2. Glycolysis, through the formation of pyruvate, includes a single oxidation step:

> D-Glyceraldehyde-3-Phosphate + NAD+ + Pi <=> 1,3 Bisphosphoglycerate + NADH + H+

> Because there are two molecules of G3P per molecule of glucose, there is a total of two molecules of NADH formed per molecule of glucose.

> 3. 1,3BPG and PEP are phosphorylated compounds, each with a phosphoryl group that has a free energy higher than that of the phosphate on ADP. Thus 1,3BPG and PEP can transfer a phosphoryl group to ADP to form ATP. This is called substrate level phosphorylation and it yields four molecules of ATP per molecule of glucose in the energy releasing phase of glycolysis. Thus, the 10 reactions of glycolysis generate two net molecules of ATP per molecule of glucose.

See also: Reactions/Energies of Glycolysis, Regulation of Glycolysis, Hexokinase