Core subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I) which catalyzes electron transfer from NADH through the respiratory chain, using ubiquinone as an electron acceptor (PubMed:16996290). Essential for the catalytic activity and assembly of complex I (PubMed:16996290). . This is the function of MT-ND2 (mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 2, ENSG00000198763).