GLOSSARY

HMG-CoA Reductase converts HMG-CoA to mevalonate in cholesterol biosynthesis.

The liver receives nutrients from the intestine and systemic circulation and can transform, store or release them. First pass generally concerns removal before systemic appearance and, depending on the definition, includes intestinal and hepatic contributions. Net hepatic extraction does not reveal every intrahepatic fate; concentration, blood flow and the measurement boundary must be specified before calculating it.

Fatty-acid synthesis builds chains from smaller units; lipogenesis can more broadly include lipid production and storage. De novo synthesis differs from esterifying existing fatty acids. Liver and adipose contributions depend on nutritional state and require energy and reducing equivalents. Eating carbohydrate does not immediately turn all of it into fat. Stores, oxidation, total intake and time determine carbon routing, so one synthetic pathway should not be treated as the inevitable fate of every carbohydrate meal.

Location determines access to substrates, cofactors and local conditions. Cytosol, mitochondrial matrix, peroxisomes and nucleus are not equivalent environments. Microsomal usually refers to a laboratory membrane fraction largely derived from endoplasmic reticulum, not a normal independent organelle in living cells. Direct transfer of intermediates between enzymes requires evidence; proximity or membership of the same compartment alone does not establish substrate channeling or its magnitude.