Gluconeogenesis
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
The synthesis of glucose from non-carbohydrate precursors (lactate, glycerol, amino acids) — essentially glycolysis in reverse with three bypass reactions.
Gluconeogenesis in plain English
Gluconeogenesis literally means 'making new glucose,' and your body does it when blood sugar runs low — say, hours into sleep or a long run — but your brain still demands glucose to keep working. Instead of using dietary carbs, it BUILDS glucose from scraps like lactate (from tired muscles), glycerol (from fat), and amino acids (from protein). It's almost exactly glycolysis (the sugar-burning pathway) run backwards, but three of glycolysis's steps are one-way streets that can't simply reverse, so the body uses three special detour reactions to get around them. It's like reassembling a smashed Lego castle: mostly you just reverse the steps, but a few spots need a different tool to put back together.
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