Glycolysis ATP Payoff Phase

Study Notes

Glycolysis converts glucose into two pyruvate molecules, generating four ATP molecules in the process.
Pyruvate can be transformed into lactate or enter the mitochondria to participate in the TCA cycle.

Hexokinase catalyzes the conversion of glucose to glucose 6-phosphate, initiating glycolysis.
Fructose 6-phosphate is formed from glucose 6-phosphate before phosphorylation to fructose 1,6-bisphosphate.
Aldolase splits fructose 1,6-bisphosphate into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate.
Two molecules of glyceraldehyde 3-phosphate are produced and further processed to generate 1,3-bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase.
1,3-bisphosphoglycerate is converted to 3-phosphoglycerate, yielding ATP via phosphoglycerate kinase.

The ATP investment phase consumes ATP while the ATP payoff phase produces ATP.
Three irreversible reactions, occurring at steps 1, 3, and 10, are crucial for glycolysis due to their large negative Gibbs free energy (ΔG).

Reactions driven forward by the concentration of reactants, enzyme activity, and removal of products, maintaining a favorable Gibbs free energy.
Hexokinases (HKI–IV) facilitate the first step of glycolysis, with their activity regulated by metabolites and transcription factors.

3-Phosphoglycerate can be converted to serine, leading to the amino acids cysteine and glycine.
Pyruvate serves as a precursor for various biosynthetic pathways, including the production of alanine.

In mammals, pyruvate can convert to lactate via lactate dehydrogenase.
In yeast, pyruvate is converted to acetaldehyde and then to ethanol, illustrating the differing pathways of fermentation.

Lactate, pyruvate, and acetaldehyde play essential roles in energy metabolism and biosynthetic processes.
Metabolite concentration and enzyme regulation dictate the balance between energy generation and biosynthetic activities.