Foundational Sciences (General Principles)

The conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, catalyzed by phosphofructokinase-1 (PFK-1). It is allosterically activated by AMP and fructose-2,6-bisphosphate, and inhibited by ATP and citrate.

Glucokinase. It has a high Km (low affinity) and high Vmax, is not inhibited by glucose-6-phosphate, and is induced by insulin — letting the liver sequester glucose only when blood glucose is high.

Net 2 ATP and 2 NADH per glucose. Substrate-level: 4 ATP made (phosphoglycerate kinase, pyruvate kinase steps) minus 2 ATP consumed (hexokinase/glucokinase and PFK-1 steps).

RBCs lack mitochondria, so they cannot perform oxidative phosphorylation or the TCA cycle. They regenerate NAD+ by converting pyruvate to lactate via lactate dehydrogenase, producing only 2 net ATP per glucose.

The Rapoport-Luebering shunt diverts 1,3-BPG to 2,3-BPG (bypassing an ATP-generating step). 2,3-BPG binds deoxyhemoglobin and decreases its O2 affinity, shifting the oxyhemoglobin curve right to favor O2 unloading in tissues.

Deficiency of galactose-1-phosphate uridyltransferase (GALT). Galactose-1-phosphate accumulates, causing jaundice, hepatomegaly, cataracts, intellectual disability, and E. coli sepsis in neonates. Treat by excluding galactose/lactose.