Glycolysis, Gluconeogenesis, and Related Metabolism

A comprehensive set of 200 vocabulary flashcards covering key enzymes, intermediates, mechanisms, regulatory concepts, and metabolic pathways related to glycolysis, gluconeogenesis, fermentation, and associated carbohydrate metabolism topics from the lecture notes.

Glycolysis

Ten-step cytosolic pathway that converts glucose into pyruvate with a net gain of 2 ATP and 2 NADH.

Gluconeogenesis

Liver- and kidney-based pathway that synthesizes glucose from non-carbohydrate precursors such as lactate, glycerol, and amino acids.

Pentose Phosphate Pathway

Oxidative pathway that produces NADPH and ribose-5-phosphate from glucose-6-phosphate.

Hexokinase

Enzyme catalyzing ATP-dependent phosphorylation of glucose to glucose-6-phosphate in glycolysis step 1.

Phosphofructokinase-1 (PFK-1)

Key regulatory enzyme that converts fructose-6-phosphate to fructose-1,6-bisphosphate using ATP.

Fructose 1,6-bisphosphatase-1 (FBPase-1)

Gluconeogenic enzyme that hydrolyzes fructose-1,6-bisphosphate to fructose-6-phosphate.

Aldolase

Enzyme that cleaves fructose-1,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.

Triose Phosphate Isomerase (TPI)

Enzyme that rapidly interconverts dihydroxyacetone phosphate and glyceraldehyde-3-phosphate.

Glyceraldehyde 3-phosphate dehydrogenase (GAPDH)

Enzyme that oxidizes GAP to 1,3-bisphosphoglycerate while reducing NAD+ to NADH.

Phosphoglycerate Kinase (PGK)

Enzyme transferring phosphate from 1,3-BPG to ADP, producing ATP and 3-phosphoglycerate.

Phosphoglycerate Mutase (PGM)

Enzyme that relocates phosphate from C-3 to C-2 of 3-phosphoglycerate to form 2-phosphoglycerate.

Enolase

Lyase that dehydrates 2-phosphoglycerate to form phosphoenolpyruvate (PEP).

Pyruvate Kinase

Enzyme that converts PEP and ADP to pyruvate and ATP in glycolysis’ final step.

Substrate-level Phosphorylation

Direct synthesis of ATP by transfer of a high-energy phosphate group to ADP.

Oxidative Phosphorylation (glycolytic context)

Step 6 reaction where GAP is oxidized and Pi incorporated, coupling NAD+ reduction to high-energy phosphate formation.

NAD+

Oxidized nicotinamide adenine dinucleotide that accepts electrons in metabolic redox reactions.

NADH

Reduced form of NAD+ that carries high-energy electrons to later processes or fermentation.

ATP

Universal cellular energy currency containing two high-energy phosphoanhydride bonds.

ADP

Adenosine diphosphate; product of ATP hydrolysis and substrate for new ATP formation.

Inorganic Phosphate (Pi)

Free phosphate ion used in phosphorylation reactions such as GAP oxidation.

Preparatory Phase of Glycolysis

First five glycolytic reactions that consume ATP to convert glucose into two GAP molecules.

Payoff Phase of Glycolysis

Last five glycolytic steps that produce NADH and ATP while converting GAP to pyruvate.

Glucose

Six-carbon aldose sugar serving as primary cellular fuel and versatile metabolic precursor.

Pyruvate

Three-carbon α-keto acid produced at glycolysis’ end; precursor for lactate, ethanol, acetyl-CoA etc.

Phosphoenolpyruvate (PEP)

Highest-energy phosphate compound formed by enolase and donor in ATP synthesis by pyruvate kinase.

1,3-Bisphosphoglycerate (1,3-BPG)

High-energy acyl-phosphate intermediate produced by GAPDH.

3-Phosphoglycerate (3-PG)

Product of phosphoglycerate kinase and substrate for phosphoglycerate mutase.

2-Phosphoglycerate (2-PG)

Intermediate formed from 3-PG by PGM and dehydrated by enolase.

Glyceraldehyde 3-phosphate (GAP)

Three-carbon aldehyde phosphate that enters glycolysis’ payoff phase.

Dihydroxyacetone Phosphate (DHAP)

Ketose phosphate produced by aldolase and isomerized to GAP.

Glucose 6-phosphate (G6P)

Phosphorylated glucose trapped inside the cell; branch point for multiple pathways.

Fructose 6-phosphate (F6P)

Isomerized product of G6P and substrate for PFK-1.

Fructose 1,6-bisphosphate (F1,6BP)

Doubly phosphorylated sugar committing glucose to glycolysis.

Glycogen

Branched polymer of glucose serving as animal storage carbohydrate.

Starch

Plant storage polysaccharide composed of amylose and amylopectin.

Storage Polysaccharides

Large glucose polymers such as glycogen and starch used to reserve energy.

NADPH

Reduced nicotinamide adenine dinucleotide phosphate used in reductive biosynthesis and antioxidation.

Ribose 5-phosphate

Five-carbon sugar produced in the pentose phosphate pathway for nucleotide synthesis.

Structural Carbohydrates

Polysaccharides used to build cell walls or extracellular matrices, e.g., cellulose and chitin.

Fermentation

Anaerobic process converting pyruvate to reduced products while regenerating NAD+.

Lactic Acid Fermentation

Conversion of pyruvate to lactate by LDH, regenerating NAD+ in muscle and erythrocytes.

Alcohol (Ethanol) Fermentation

Two-step reduction of pyruvate to ethanol and CO₂ performed by yeast.

Lactate Dehydrogenase (LDH)

Enzyme that catalyzes reversible reduction of pyruvate to lactate using NADH.

Pyruvate Decarboxylase

Thiamine-dependent enzyme that removes CO₂ from pyruvate to form acetaldehyde.

Alcohol Dehydrogenase

Zinc-dependent enzyme that reduces acetaldehyde to ethanol using NADH.

Thiamine Pyrophosphate (TPP)

Vitamin B₁-derived coenzyme that stabilizes carbanion intermediates in decarboxylations.

Mg²⁺ Cofactor

Divalent metal ion that stabilizes negative charges on ATP and activates many kinases.

Zn²⁺ Cofactor

Metal ion that polarizes carbonyls in enzymes such as alcohol dehydrogenase.

Biotin

Vitamin-derived coenzyme that carries CO₂ groups in carboxylation reactions like pyruvate carboxylase.

Carboxylation

Addition of CO₂ to a substrate, often using biotin as a carrier.

Oxaloacetate (OAA)

Four-carbon α-keto dicarboxylate produced from pyruvate; intermediate in gluconeogenesis and the TCA cycle.

Pyruvate Carboxylase

Mitochondrial biotin enzyme that converts pyruvate to oxaloacetate using ATP and CO₂.

Phosphoenolpyruvate Carboxykinase (PEPCK)

Enzyme that converts oxaloacetate to PEP using GTP and releasing CO₂.

Malate

Four-carbon dicarboxylate that transports reducing equivalents and carbon skeletons across mitochondrial membranes.

Mitochondrial Shuttle

Mechanism that moves metabolites like malate or PEP between mitochondrion and cytosol.

Cori Cycle

Metabolic pathway shuttling lactate from muscle to liver for gluconeogenesis and returning glucose.

Warburg Effect

Preference of cancer cells for high glycolytic rates even in the presence of oxygen.

Tumor Glycolysis

Enhanced glucose consumption and lactate secretion characteristic of many cancers.

Glycogen Phosphorylase

Enzyme that releases glucose-1-phosphate from glycogen using inorganic phosphate.

α-Amylase

Digestive enzyme that hydrolyzes internal α(1→4) links in starch and glycogen.

Hexose

Six-carbon monosaccharide such as glucose or fructose.

Ketose

Monosaccharide containing a ketone functional group; fructose is an example.

Enediol Intermediate

Transient double-bonded species formed during aldose–ketose isomerization.

Covalent Catalysis

Enzyme mechanism involving temporary covalent bonding between enzyme and substrate.

General Acid-Base Catalysis

Enzymatic use of proton donors or acceptors other than water to accelerate reactions.

Schiff Base

Covalent imine linkage between an enzyme lysine and a carbonyl substrate, stabilizing intermediates.

Thioester Intermediate

High-energy sulfur-ester bond formed between a cysteine residue and substrate in GAPDH.

Substrate Channeling

Direct transfer of intermediates between enzyme active sites without diffusion into the solvent.

Isoforms

Different molecular forms of an enzyme encoded by separate genes (e.g., hexokinase I–IV).

Glucokinase (Hexokinase IV)

Liver-specific hexokinase isozyme with high Km that functions in glucose uptake post-meal.

Substrate Inhibition

Regulation where high substrate concentration lowers enzyme activity.

Allosteric Regulation

Modulation of enzyme activity through binding of effectors at sites other than the active site.

Feedback Inhibition

End-product binding to an early pathway enzyme to reduce pathway flux.

ATP as Allosteric Inhibitor

ATP acts as a negative effector on PFK-1, signaling high cellular energy.

Fructose 2,6-bisphosphate

Potent positive regulator of PFK-1 and inhibitor of FBPase-1.

Futile Cycle

Simultaneous operation of opposing pathways, wasting energy as heat.

Energy Charge

Ratio reflecting cellular ATP, ADP, and AMP levels that regulates metabolic pathways.

Triose Kinase

Enzyme that phosphorylates glyceraldehyde to GAP using ATP in fructose metabolism.

Feeder Pathways

Metabolic routes that convert dietary sugars or glycogen into glycolytic intermediates.

Galactokinase

Enzyme that phosphorylates galactose to galactose-1-phosphate.

Trehalase

Intestinal enzyme that hydrolyzes trehalose into two glucose molecules.

Lactase

β-galactosidase enzyme that splits lactose into glucose and galactose.

Sucrase

Intestinal enzyme that hydrolyzes sucrose into glucose and fructose.

Galactose-1-phosphate Uridylyltransferase

Enzyme that exchanges UDP between glucose and galactose phosphates in galactose metabolism.

UDP-Glucose

Activated glucose donor used in glycogen synthesis and galactose conversion.

Epimerase

Enzyme that interconverts stereoisomers, e.g., UDP-glucose 4-epimerase.

UDP-Galactose

UDP-activated form of galactose produced from UDP-glucose.

Mannose 6-phosphate

Phosphorylated mannose that enters glycolysis after isomerization to fructose 6-phosphate.

Phosphomannose Isomerase

Enzyme that converts mannose-6-phosphate to fructose-6-phosphate.

Ketogenic Amino Acid

Amino acid whose degradation yields only acetyl-CoA or acetoacetate, not glucose.

Glucogenic Amino Acid

Amino acid that can be degraded to pyruvate or TCA intermediates for gluconeogenesis.

Anabolic Pathway

Metabolic route that synthesizes complex molecules from simpler precursors, requiring energy.

Catabolic Pathway

Metabolic route that breaks down molecules to release energy and reducing power.

Aerobic Glycolysis

Glycolysis occurring when oxygen is present; pyruvate typically enters the TCA cycle.

Anaerobic Glycolysis

Glycolysis under oxygen-limited conditions where NAD+ is regenerated by fermentation.

Rate-Limiting Step

Slowest highly regulated reaction that controls the overall pathway flux.

Committed Step

First irreversible step unique to a pathway, ensuring metabolites proceed forward.

High-Energy Phosphate Compound

Molecule whose hydrolysis releases large negative free energy capable of phosphorylating ADP.

Tautomerization

Rearrangement of bonds in an enol to a more stable keto form, driving ATP formation by pyruvate kinase.

Substrate-Level ATP Production

ATP synthesis that occurs directly in glycolysis without an electron transport chain.