Metabolic Pathway Enzymes Flashcards by Dann Caryl Robin Vasquez

Phosphorylates glucose to glucose-6-phosphate (G6P), trapping it inside the cell.

Hexokinase / Glucokinase

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Converts glucose-6-phosphate into fructose-6-phosphate.

Phosphoglucose Isomerase (PGI)

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Converts fructose-6-phosphate into fructose-1,6-bisphosphate (rate-limiting step).

Phosphofructokinase-1 (PFK-1)

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Splits fructose-1,6-bisphosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P).

Aldolase

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Converts DHAP into G3P.

Triose Phosphate Isomerase (TPI)

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Oxidizes G3P to 1,3-bisphosphoglycerate (producing NADH).

Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH)

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Converts 1,3-bisphosphoglycerate to 3-phosphoglycerate (producing ATP).

Phosphoglycerate Kinase (PGK)

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Converts 3-phosphoglycerate into 2-phosphoglycerate.

Phosphoglycerate Mutase (PGM)

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Converts 2-phosphoglycerate into phosphoenolpyruvate (PEP).

Enolase

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Converts PEP into pyruvate (producing ATP).

Pyruvate Kinase (PK)

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Converts acetyl-CoA and oxaloacetate into citrate.

Citrate Synthase

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Converts citrate into isocitrate via cis-aconitate.

Aconitase

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Converts isocitrate into α-ketoglutarate (producing NADH and CO₂).

Isocitrate Dehydrogenase

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Converts α-ketoglutarate into succinyl-CoA (producing NADH and CO₂).

α-Ketoglutarate Dehydrogenase

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Converts succinyl-CoA into succinate (producing GTP/ATP).

Succinyl-CoA Synthetase

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Converts succinate into fumarate (producing FADH₂).

Succinate Dehydrogenase

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Converts fumarate into malate.

Fumarase

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Converts malate into oxaloacetate (producing NADH).

Malate Dehydrogenase

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Converts glucose-6-phosphate into 6-phosphogluconolactone (producing NADPH).

Glucose-6-Phosphate Dehydrogenase (G6PD)

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Converts 6-phosphogluconolactone into 6-phosphogluconate.

6-Phosphogluconolactonase

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Converts 6-phosphogluconate into ribulose-5-phosphate (producing NADPH and CO₂).

6-Phosphogluconate Dehydrogenase

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Converts ribulose-5-phosphate into ribose-5-phosphate.

Ribulose-5-Phosphate Isomerase

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Transfers 2-carbon units between sugars.

Transketolase

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Transfers 3-carbon units between sugars.

Transaldolase

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Cleaves glycogen into glucose-1-phosphate.

Glycogen Phosphorylase

Converts glucose-1-phosphate into glucose-6-phosphate

Phosphoglucomutase

Removes branches in glycogen, allowing complete breakdown.

Debranching Enzyme (α-1,6-Glucosidase & Transferase Activity)

Converts glucose-6-phosphate into free glucose (only in the liver).

Glucose-6-Phosphatase

Converts glucose into glucose-6-phosphate.

Hexokinase / Glucokinase

Converts glucose-6-phosphate into glucose-1-phosphate.

Phosphoglucomutase

Converts glucose-1-phosphate into UDP-glucose.

UDP-Glucose Pyrophosphorylase

Adds UDP-glucose to glycogen primer.

Glycogen Synthase

Creates α-1,6 branches in glycogen.

Branching Enzyme (1,4-α-Glucan Branching Enzyme)

Uses light to split water into oxygen, electrons, and protons.

Photosystem II (PSII)

Transfers electrons from PSII to cytochrome b6f.

Plastoquinone (PQ)

In photosynthesis, it facilitates electron transfer and pumps protons.

Cytochrome b6f Complex

Transfers electrons to Photosystem I.

Plastocyanin (PC)

Uses light to energize electrons and pass them to NADP⁺.

Photosystem I (PSI)

Converts NADP⁺ into NADPH.

Ferredoxin-NADP+ Reductase (FNR)

Synthesizes ATP from ADP using a proton gradient.

ATP Synthase

Fixes CO₂ into organic molecules.

Ribulose-1,5-Bisphosphate Carboxylase (RuBisCO)

Converts 3-phosphoglycerate into 1,3-bisphosphoglycerate.

Phosphoglycerate Kinase

Produces glyceraldehyde-3-phosphate.

Glyceraldehyde-3-Phosphate Dehydrogenase

Rearranges carbon skeletons to regenerate ribulose-1,5-bisphosphate.

Transketolase / Aldolase

Functions as a proton channel. H⁺ ions flow down the electrochemical gradient from intermembrane space to the matrix (mitochondria) or from thylakoid lumen to the stroma (chloroplasts).

F₀ Subunit (Membrane-embedded portion)

Functions as an ATP synthesizing unit. The γ subunit rotates due to F₀ rotation, causing conformational changes in the β-subunits, driving ATP synthesis.

F₁ Subunit (Cytoplasmic/matrix-exposed portion)

F₀ Subunit (Proton Channel) - Forms a proton channel that allows H⁺ ions to pass through.

a Subunit

Acts as a structural stabilizer, connecting F₀ to F₁

b Subunit

Rotates when protons move through, driving ATP synthesis in F₁.

c Subunit (c-Ring)

Structural components that help in ATP binding and release.

α (Alpha) Subunits (x3)

Active sites for ATP synthesis (catalytic subunits).

β (Beta) Subunits (x3)

Rotates and induces conformational changes in β-subunits, enabling ATP production.

γ (Gamma) Subunit

Provides stability by linking α and β subunits to the stator.

δ (Delta) Subunit

Regulates the rotation of γ and prevents reverse rotation

ε (Epsilon) Subunit

States of β-Subunit: Binds ADP + Pi weakly.

Loose (L) State

States of β-Subunit: Catalyzes the conversion of ADP + Pi → ATP.

Tight (T) State

States of β-Subunit: Releases ATP and resets to accept new ADP + Pi.

Open (O) State

Converts triglycerides into diglycerides by removing one fatty acid.

Adipose Triglyceride Lipase (ATGL)

Converts diglycerides into monoglycerides by removing another fatty acid.

Hormone-Sensitive Lipase (HSL)

Converts monoglycerides into glycerol and free fatty acids.

Monoacylglycerol Lipase (MGL)

Activates free fatty acids by converting them into Acyl-CoA.

Acyl-CoA Synthetase (Fatty Acid Thiokinase)

Transfers Acyl-CoA into mitochondria by converting it into Acyl-Carnitine.

Carnitine Palmitoyltransferase I (CPT I)

Converts Acyl-Carnitine back into Acyl-CoA inside mitochondria.

Carnitine Palmitoyltransferase II (CPT II)

Converts Acyl-CoA into trans-Δ²-Enoyl-CoA (producing FADH₂).

Acyl-CoA Dehydrogenase

Converts trans-Δ²-Enoyl-CoA into L-3-Hydroxyacyl-CoA (hydration step).

Enoyl-CoA Hydratase

Converts L-3-Hydroxyacyl-CoA into 3-Ketoacyl-CoA (producing NADH).

3-Hydroxyacyl-CoA Dehydrogenase.

Cleaves 3-Ketoacyl-CoA to release Acetyl-CoA for the Krebs cycle.

β-Ketothiolase (Thiolase)

Condenses two Acetyl-CoA molecules to form Acetoacetyl-CoA.

Thiolase (Acetoacetyl-CoA Thiolase)

Adds another Acetyl-CoA to form 3-Hydroxy-3-Methylglutaryl-CoA (HMG-CoA)

HMG-CoA Synthase

Converts HMG-CoA into Acetoacetate (first ketone body).

HMG-CoA Lyase

Converts Acetoacetate into β-Hydroxybutyrate (second ketone body).

β-Hydroxybutyrate Dehydrogenase

Converts some Acetoacetate into Acetone (third ketone body, exhaled).

Acetoacetate Spontaneous Decarboxylation

Converts Acetyl-CoA into Malonyl-CoA (rate-limiting step).

Acetyl-CoA Carboxylase (ACC)

A multi-enzyme complex that elongates fatty acids step by step.

Fatty Acid Synthase (FAS) Complex

Condenses Acetyl-CoA and Malonyl-CoA to form β-Ketoacyl-ACP

β-Ketoacyl Synthase

Converts β-Ketoacyl-ACP into β-Hydroxyacyl-ACP using NADPH.

β-Ketoacyl Reductase

Removes water from β-Hydroxyacyl-ACP to form Enoyl-ACP.

β-Hydroxyacyl Dehydratase

Converts Enoyl-ACP into Saturated Acyl-ACP, elongating the fatty acid.

Enoyl-ACP Reductase

Cleaves the final Palmitoyl-ACP to release Palmitate (C16:0 fatty acid).

Thioesterase

Converts Glycerol into Glycerol-3-Phosphate (liver only).

Glycerol Kinase

Converts Dihydroxyacetone Phosphate (DHAP) into Glycerol-3-Phosphate.

Glycerol-3-Phosphate Dehydrogenase

Activates fatty acids by converting them into Acyl-CoA.

Acyl-CoA Synthetase

Adds the first Acyl-CoA to Glycerol-3-Phosphate to form Lysophosphatidic Acid.

Glycerol-3-Phosphate Acyltransferase (GPAT)

Adds a second Acyl-CoA to form Phosphatidic Acid.

1-Acylglycerol-3-Phosphate Acyltransferase (AGPAT)

Removes phosphate from Phosphatidic Acid, forming Diacylglycerol (DAG).

Phosphatidic Acid Phosphatase (Lipin)

Adds the third Acyl-CoA to form Triglyceride (TAG).

Diacylglycerol Acyltransferase (DGAT)

Converts Acetyl-CoA into Acetoacetyl-CoA.

Thiolase

Converts Acetoacetyl-CoA into HMG-CoA.

HMG-CoA Synthase

Converts HMG-CoA into Mevalonate (rate-limiting step).

HMG-CoA Reductase

Converts Mevalonate into Mevalonate-5-Phosphate.

Mevalonate Kinase

Converts Mevalonate-5-Phosphate into Mevalonate-5-Pyrophosphate

Phosphomevalonate Kinase

Converts Mevalonate-5-Pyrophosphate into Isopentenyl Pyrophosphate (IPP).

Mevalonate-5-Pyrophosphate Decarboxylase

Converts IPP into Dimethylallyl Pyrophosphate (DMAPP).

Isopentenyl Pyrophosphate Isomerase

Combines IPP and DMAPP into Geranyl Pyrophosphate (GPP).

Prenyltransferase

Converts Farnesyl Pyrophosphate (FPP) into Squalene.

Squalene Synthase

Converts Squalene into Lanosterol.

Squalene Epoxidase

Converts Lanosterol into Cholesterol.

Lanosterol 14α-Demethylase