Pyruvic acid synthesized in glycolysis must enter inside the mitochondria, where oxidative decarboxylation occurs in the presence of NAD⁺ and coenzyme-A. This results in the formation of acetyl CoA which can enter the Kreb's cycle. This reaction is catalyzed by pyruvate dehydrogenase. 

Succinate dehydrogenase enzyme is present on inner membrane of mitochondria and is a part of the complex II in the ETC. It catalyses the oxidation of succinate to fumarate in the Kreb's cycle and channels the FADH2 produced during this reaction into the ETC.

Glycolysis is a series of reactions that takes place in the cytoplasm of all prokaryotes and eukaryotes. The role of glycolysis is to produce energy (both directly and by supplying substrate for the citric acid cycle and oxidative phosphorylation) and to produce intermediates for biosynthetic pathway.