BC 14: Glycolysis, Gluconeogenesis, and PPP

Glycolysis

Breaks a glucose molecule via enzyme-catalyzed reactions into two 3C pyruvate molecules.

Isozymes

2+ enzymes catalyzing the same reaction but encoded by different genes.

Substrate-level phosphorylation

Make ATP by transferring a phosphoryl group from a substrate to ADP using soluble enzymes and chemical intermediates.

Respiration-linked phosphorylation

ATP production involving membrane-bound enzymes and transmembrane protein gradients.

Glycogen phosphorylase

Phosphorolyzes glycogen to yield glucose 1-phosphate in animal tissues and microorganisms.

Starch phosphorylase

Phosphorolyzes starch.

Phosphoglycomutase

Interconverts glucose 1-phosphate and glucose 6-phosphate.

Mutase

An isomerase that moves a functional group within a molecule.

Alpha-amylase

Salivary and small intestine enzyme hydrolyzing internal alpha(1-4) links of starch and glycogen into di/trisaccharides.

Limit dextrins

Amylopectin fragments containing alpha(1-6) bonds, removed by limit dextrinases.

Cellulase

Enzyme attacking beta(1-4) bonds of cellulose (absent in most animals).

Lactase persistence phenotype

Allows production of lactase (converting lactose to glucose and galactose) into adulthood.

Galactokinase

Uses ATP to phosphorylate galactose at C1.

Fructose 1-phosphate aldolase

Cleaves fructose 1-phosphate in the liver into glyceraldehyde and dihydroxyacetone phosphate.

Triose kinase

Uses ATP to phosphorylate glyceraldehyde to glyceraldehyde 3-phosphate.

Hexokinase

Phosphorylates mannose at C6; phosphohexose isomerase converts that to fructose 6-phosphate for glycolysis.

Fermentation

Processes extracting ATP without consuming O2 or changing net [NAD+]/[NADH].

Lactic acid fermentation

Pyruvate is reduced by NADH to lactate, regenerating NAD+ for glycolysis.

Ethanol (alcohol) fermentation

Pyruvate loses CO2 to form acetaldehyde, which is then reduced to ethanol.

Pyruvate decarboxylase

Irreversibly decarboxylates pyruvate to acetaldehyde (requires Mg2+ and TPP).

Alcohol dehydrogenase

Reduces acetaldehyde to ethanol.

Thiamine pyrophosphate (TPP)

Vitamin B1-derived coenzyme allowing cleavage of bonds adjacent to a carbonyl group.

Lactate dehydrogenase

Catalyzes pyruvate-to-lactate reduction; lactate is recycled to glucose in the liver during recovery.

Gluconeogenesis

Converts pyruvate and 3C/4C compounds to glucose (occurs in all life domains; mainly in liver for mammals).

Glucogenic amino acids

Amino acids that can be converted into glucose.

Glyceroneogenesis

Truncated gluconeogenesis converting pyruvate to dihydroxyacetone phosphate, then reducing it to glycerol 3-phosphate.

Glucagon

Hormone signaling the liver to produce/release glucose and stop consuming it.

ChREBP

Transcription factor in liver, fat, and kidney; dephosphorylated twice (in cytosol then nucleus) to regulate carbohydrate/fat synthesis genes.

Pentose phosphate pathway (PPP)

Oxidizes glucose 6-phosphate to make pentose phosphates and NADPH. Needed by cells that need ribose 5-phosphate and NADPH (for synth cholesterol/steroid hormones or fatty acids)

Reductive pentose phosphate pathway

Converts hexose phosphates to pentose phosphates; reverses nonoxidative PPP reactions for plant CO2 use.