What is pyruvate and why is it considered a keystone molecule in metabolism?

Pyruvate is a keystone molecule critical for numerous aspects of eukaryotic and human metabolism. It is the end-product of glycolysis, derived from additional sources in the cellular cytoplasm, and is ultimately transported into mitochondria as a master fuel input for the citric acid cycle. Pyruvate drives ATP production through oxidative phosphorylation and supports various biosynthetic pathways intersecting the citric acid cycle.