Biochemistry of Eicosanoids, Amino Acid Metabolism, and One-Carbon Metabolism

A comprehensive set of 100 vocabulary flashcards covering the biochemistry of signaling lipids, amino acid synthesis/catabolism, ammonia detoxification, and one-carbon metabolism cofactors.

Eicosanoids

Signaling molecules derived from arachidonic acid or other polyunsaturated fatty acids that regulate inflammation, immunity, and physiological processes.

Prostaglandins (PGs)

A major class of eicosanoids that mediate inflammation, protect the gastric mucosa, and regulate smooth muscle contraction.

Thromboxanes (TXs)

A class of eicosanoids, specifically $TXA_2$, primarily involved in platelet aggregation and vasoconstriction.

Leukotrienes (LTs)

Eicosanoids produced via the lipoxygenase pathway that promote inflammation and bronchoconstriction.

Lipoxins (LXs)

Anti-inflammatory eicosanoids that help resolve inflammation.

Phospholipase $A_2$ ($PLA_2$)

The key enzyme that hydrolyzes membrane phospholipids to release arachidonic acid.

Arachidonic acid

A polyunsaturated fatty acid that serves as the primary precursor for the synthesis of eicosanoids.

Cyclooxygenase-1 (COX-1)

An enzyme responsible for producing protective prostaglandins ($PGI_2$) in the gastric mucosa.

Cyclooxygenase-2 (COX-2)

An enzyme that converts arachidonic acid into $PGH_2$; its activity can be modified by aspirin to produce anti-inflammatory lipoxins.

Prostaglandin $H_2$ ($PGH_2$)

The precursor molecule for both prostaglandins and thromboxanes produced by COX enzymes.

5-Lipoxygenase (5-LOX)

The specific enzyme in the lipoxygenase pathway that converts arachidonic acid into leukotrienes.

Prostaglandin $E_2$ ($PGE_2$)

A specific prostaglandin known for mediating inflammation.

Prostacyclin ($PGI_2$)

A prostaglandin that protects the gastric mucosa and is reduced by the inhibition of COX-1.

Thromboxane $A_2$ ($TXA_2$)

A potent vasoconstrictor and mediator of blood clot formation through platelet aggregation.

NSAIDs

Nonsteroidal anti-inflammatory drugs that inhibit COX-1 and COX-2 enzymes to reduce pain and inflammation.

Corticosteroids

Drugs that inhibit $PLA_2$, preventing the release of arachidonic acid and reducing all eicosanoid production.

Leukotriene $D_4$ ($LTD_4$)

A potent bronchoconstrictor that plays a key role in the pathophysiology of asthma.

Montelukast

A leukotriene receptor antagonist used to treat asthma by blocking bronchoconstriction.

Omega-3 fatty acids

Fatty acids like EPA and DHA that compete with arachidonic acid to produce less inflammatory eicosanoids and resolvins.

Aspirin-triggered lipoxins (ATLs)

Anti-inflammatory molecules produced when aspirin acetylates COX-2, altering its enzymatic activity.

Essential Amino Acids

Amino acids that must be obtained from the diet, including Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.

Non-Essential Amino Acids

Amino acids the human body can synthesize, such as Alanine, Arginine, Asparagine, Aspartate, Cysteine, Glutamate, Glutamine, Glycine, Proline, Serine, and Tyrosine.

$3$-phosphoglycerate

A glycolysis intermediate that serves as the biosynthetic precursor for Serine, Glycine, and Cysteine.

Alanine

A non-essential amino acid synthesized via the transamination of pyruvate.

Oxaloacetate

A citric acid cycle intermediate used to synthesize Aspartate and Asparagine.

$α$-ketoglutarate

A citric acid cycle intermediate that serves as a precursor for Glutamate, Glutamine, Proline, and Arginine.

Ribose-$5$-phosphate

An intermediate from the pentose phosphate pathway used to synthesize Histidine.

Transaminases

Enzymes that catalyze the transfer of amino groups between amino acids and $α$-keto acids.

Glutamine Synthetase

The enzyme that converts glutamate into glutamine using $ATP$ and ammonia.

Aspartate Aminotransferase (AST)

An enzyme that mediates transamination reactions involving aspartate and oxaloacetate.

Alanine Aminotransferase (ALT)

An enzyme that mediates transamination reactions, converting alanine and $α$-ketoglutarate into pyruvate and glutamate.

Transamination

The first step of amino acid degradation involving the removal of the amino group via aminotransferases.

Oxidative Deamination

The release of ammonia from glutamate, catalyzed by glutamate dehydrogenase.

Urea Cycle

A metabolic pathway in the liver that detoxifies ammonia by converting it into urea for excretion.

Glucogenic Amino Acids

Amino acids that can be converted into glucose via gluconeogenesis, such as alanine, aspartate, and glutamate.

Ketogenic Amino Acids

Amino acids converted into ketone bodies or $acetyl-CoA$, with Leucine and Lysine being exclusive examples.

Branched-chain $α$-ketoacid dehydrogenase complex (BCKDH)

Enzyme complex responsible for the oxidative decarboxylation of leucine, isoleucine, and valine.

Maple Syrup Urine Disease (MSUD)

A metabolic disorder caused by a deficiency in BCKDH, leading to the accumulation of branched-chain amino acids.

Phenylalanine hydroxylase

The enzyme that converts phenylalanine to tyrosine; its deficiency causes Phenylketonuria.

Phenylketonuria (PKU)

An inborn error of metabolism resulting in the accumulation of phenylalanine due to a defect in phenylalanine hydroxylase.

Alkaptonuria

A deficiency in homogentisate oxidase that leads to the accumulation of homogentisic acid and black urine.

Glutaminolysis

Increased glutamine metabolism that supports tumor growth in cancer cells.

Hyperammonemia

Elevated blood ammonia levels resulting from liver failure or genetic defects in the urea cycle, causing neurotoxicity.

Glutamate dehydrogenase (GDH)

Enzyme that performs oxidative deamination to release free ammonia and regenerate $α$-ketoglutarate.

Glutaminase

Enzyme that converts glutamine back into glutamate, releasing ammonia in tissues like the kidney and liver.

Glucose-Alanine Cycle

A process where muscle pyruvate is transaminated to alanine, transported to the liver, and converted back to pyruvate while transferring nitrogen to the urea cycle.

Carbamoyl Phosphate Synthetase I (CPS-I)

The enzyme that catalyzes the first committed step of the urea cycle in the mitochondria.

$N$-acetylglutamate (NAG)

An allosteric activator of CPS-I, produced in response to high amino acid levels.

Ornithine Transcarbamoylase (OTC)

Mitochondrial enzyme that reacts carbamoyl phosphate with ornithine to form citrulline.

Citrulline

An intermediate in the urea cycle that is transported from the mitochondria to the cytoplasm.

Argininosuccinate synthetase

Cytoplasmic enzyme that combines citrulline and aspartate using $ATP$ to form argininosuccinate.

Argininosuccinate lyase (ASL)

Enzyme that cleaves argininosuccinate into arginine and fumarate.

Arginase

Cytoplasmic enzyme that hydrolyzes arginine to produce urea and recycle ornithine.

Fumarate

A byproduct of the urea cycle that can enter the citric acid cycle ($TCA$ cycle).

Ornithine Transcarbamoylase Deficiency

The most common urea cycle disorder, characterized by X-linked recessive inheritance and orotic aciduria.

Sodium benzoate

A pharmacological agent used to treat hyperammonemia by facilitating nitrogen excretion.

Tetrahydrofolate (THF)

The biologically active form of Vitamin $B_9$ that acts as a coenzyme for transferring one-carbon units.

Folate (Vitamin $B_9$)

An essential water-soluble vitamin that is the precursor to tetrahydrofolate.

Pteridine ring

One of the three components of the THF structure, alongside PABA and a polyglutamate tail.

Para-aminobenzoic acid (PABA)

A structural component of folate and tetrahydrofolate.

$10$-formyl-THF

The form of THF that acts as a carbon donor in purine biosynthesis.

$5,10$-methylene-THF

The form of THF required for the conversion of $dUMP$ to $dTMP$ and glycine to serine.

$5$-methyl-THF

The THF form that donates a methyl group to homocysteine to regenerate methionine.

Thymidylate synthase

The enzyme that converts $dUMP$ to $dTMP$, requiring $5,10$-methylene-THF.

Formiminoglutamate (FIGLU)

An intermediate in histidine catabolism that requires THF for further processing.

Methionine synthase

A Vitamin $B_{12}$-dependent enzyme that catalyzes the conversion of homocysteine to methionine.

Megaloblastic anemia

A condition resulting from folate or Vitamin $B_{12}$ deficiency characterized by large, immature red blood cells.

Neural tube defects

Developmental conditions such as spina bifida associated with maternal folate deficiency.

Vitamin $B_{12}$ (Cobalamin)

A water-soluble vitamin containing a cobalt ion, required for DNA synthesis and fatty acid metabolism.

Corrin ring

The central chemical structure of Vitamin $B_{12}$ that coordinate a cobalt ion.

Methylcobalamin

The active form of Vitamin $B_{12}$ specifically used in methionine synthesis.

Adenosylcobalamin

The active form of Vitamin $B_{12}$ required for the methylmalonyl-CoA mutase reaction.

R-protein (Haptocorrin)

A protein in the stomach that binds to Vitamin $B_{12}$ before its release in the small intestine.

Intrinsic Factor (IF)

A glycoprotein produced by gastric parietal cells essential for Vitamin $B_{12}$ absorption in the ileum.

Transcobalamin II

A protein in the circulation that delivers Vitamin $B_{12}$ to tissues.

Methyl trap

A functional folate deficiency caused by $B_{12}$ deficiency, leading to the accumulation of $5$-methyl-THF.

Methylmalonyl-CoA Mutase

The enzyme that converts methylmalonyl-CoA into succinyl-CoA using adenosylcobalamin.

Methylmalonic acid (MMA)

A metabolite that accumulates during Vitamin $B_{12}$ deficiency but not in folate deficiency.

Pernicious anemia

An autoimmune condition involving the destruction of parietal cells, leading to a lack of intrinsic factor and $B_{12}$ deficiency.

S-Adenosyl Methionine (SAM)

The universal methyl group donor in biological methylation reactions.

Methionine adenosyltransferase

The enzyme that synthesizes SAM from methionine and $ATP$.

S-adenosylhomocysteine (SAH)

The byproduct formed after SAM donates its methyl group.

Transsulfuration pathway

A Vitamin $B_6$-dependent pathway that converts homocysteine to cystathionine.

Dihydrofolate reductase

The enzyme responsible for converting folate into the biologically active tetrahydrofolate.

Resolvins

Anti-inflammatory molecules derived from Omega-3 fatty acids that help terminate inflammation.

Arginine

An amino acid that serves as a precursor for nitric oxide synthesis and is an intermediate in the urea cycle.

Histidine

An essential amino acid whose synthesis begins from ribose-$5$-phosphate.

Valine

One of the essential branched-chain amino acids whose degradation is impaired in MSUD.

Leucine

One of the two exclusively ketogenic amino acids.

Lysine

An exclusively ketogenic essential amino acid.

Tyrosine

A non-essential amino acid synthesized from phenylalanine that is both glucogenic and ketogenic.

Homogentisate oxidase

The enzyme deficient in Alkaptonuria.

Methotrexate

A medication that can lead to folate deficiency by inhibiting folate metabolism.

Epigenetics

The study of gene expression regulation, which is influenced by SAM-mediated DNA and histone methylation.

Epinephrine

A neurotransmitter synthesized from norepinephrine via a SAM-dependent methylation reaction.

Phosphatidylcholine

A lipid produced by the SAM-dependent methylation of phosphatidylethanolamine.

Spermine and Spermidine

Polyamines involved in cell growth regulation synthesized via processes involving SAM.

Phenylbutyrate

A drug used in the treatment of urea cycle disorders to facilitate nitrogen excretion.

Orotic aciduria

A clinical finding associated with OTC deficiency due to the shunting of carbamoyl phosphate into the pyrimidine pathway.

Resolvin E1 (RvE1)

An anti-inflammatory eicosanoid derived from the Omega-3 fatty acid EPA.