Glycolysis, Gluconeogenesis and Glycogen Metabolism: every key term you need (+ practice quiz)
25 flashcard terms for Biochemistry Topic 6, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 8-question quiz — free, no account needed.
The cytosolic pathway converting one glucose to two pyruvate with a net gain of two nucleoside triphosphates and two reduced electron carriers. It runs with or without oxygen.
Investment phase
The first half of glycolysis, which consumes two nucleoside triphosphates to phosphorylate and destabilize the sugar before it is split.
Payoff phase
The second half of glycolysis, in which each three-carbon fragment is oxidized and yields two nucleoside triphosphates, doubling the initial investment.
Hexokinase
Traps glucose in the cell by phosphorylating it. It has high affinity, is inhibited by its own product, and works even when blood glucose is low.
Glucokinase
The liver and pancreatic isoform with low affinity and no product inhibition, so it accelerates only when glucose is abundant and acts as a glucose sensor.
Phosphofructokinase-1
The main regulated and committed step of glycolysis. It is inhibited by high energy charge and citrate and activated when the cell signals a need for energy.
Fructose 2,6-bisphosphate
A regulatory molecule, not a pathway intermediate, that strongly activates the committed glycolytic step and inhibits its gluconeogenic counterpart.
Aldolase
Splits the six-carbon bisphosphate into two three-carbon units, one of which must be isomerized before the payoff phase can process both.
Glyceraldehyde 3-phosphate dehydrogenase
Couples oxidation of an aldehyde to formation of a high-energy acyl phosphate while reducing an electron carrier, capturing energy that would otherwise be lost as heat.
Substrate-level phosphorylation
Direct transfer of a phosphate group from a high-energy intermediate to a nucleoside diphosphate, requiring no membrane or oxygen.
Pyruvate kinase
Catalyses the final, strongly favourable glycolytic step. It is inhibited in liver by phosphorylation when blood glucose is low, sparing the substrate for export.
Lactate dehydrogenase
Reduces pyruvate to lactate to regenerate the oxidized electron carrier, allowing glycolysis to continue when oxygen or mitochondria are limiting.
Cori cycle
Muscle lactate travels to the liver, is rebuilt into glucose at energetic cost to the liver, and returns to the muscle, shifting the metabolic burden between organs.
Fructose entry
Dietary fructose is cleaved in the liver at a step downstream of the main regulated point, so it bypasses the pathway's principal brake.
Galactose entry
Galactose is phosphorylated and epimerized into a glucose derivative through a short nucleotide-sugar route before joining the main pathway.
Pentose phosphate pathway
A parallel glucose route producing reducing power for biosynthesis and five-carbon sugars for nucleotides. Its flux is set by demand for the reduced carrier, not by energy charge.
Glucose 6-phosphate dehydrogenase
The committed and rate-limiting enzyme of the pentose phosphate pathway. Deficiency leaves red cells unable to counter oxidative stress.
Gluconeogenesis
Synthesizes glucose from noncarbohydrate precursors, largely in liver and kidney. It reverses most glycolytic steps but must bypass the three irreversible ones.
Pyruvate carboxylase
Starts the bypass of the final glycolytic step by carboxylating pyruvate inside the mitochondrion. It requires a biotin cofactor and is activated by acetyl groups.
Phosphoenolpyruvate carboxykinase
Completes the first bypass by decarboxylating and phosphorylating the four-carbon intermediate, and its amount is controlled by hormonal changes in gene expression.
Fructose 1,6-bisphosphatase
Bypasses the committed glycolytic step by hydrolysing a phosphate. Reciprocal control means the signals that activate it inhibit the opposing enzyme.
Glucose 6-phosphatase
Releases free glucose in the endoplasmic reticulum of liver and kidney. Muscle lacks it, which is why muscle glycogen cannot raise blood glucose.
Glycogen phosphorylase
Cleaves glucose units from glycogen ends using phosphate rather than water, saving the cell a phosphorylation step. It is activated by phosphorylation and by calcium in muscle.
Glycogen synthase
Extends glycogen chains from a nucleotide-activated glucose donor. Phosphorylation inactivates it, so the same hormonal signal that mobilizes glycogen halts its synthesis.
Debranching enzyme
Carries a transferase and a hydrolase activity that together dismantle branch points, releasing one free glucose per branch and allowing degradation to continue.