Micronutrients in Energy Metabolism, Antioxidant Defense, and Nutritional Anemias

Comprehensive vocabulary flashcards covering micronutrients essential for energy metabolism, cellular antioxidant defense, and the prevention and pathophysiology of nutritional anemias.

Vitamer

Any of two or more closely related chemical compounds that fulfill the same specific vitamin function in the body.

Apoenzyme

The inactive protein portion of an enzyme that requires the binding of a specific vitamin coenzyme to form an active enzyme complex.

Holoenzyme

The complete, catalytically active enzyme formed by the combination of an inactive apoenzyme with its specific vitamin coenzyme.

Thiamin Pyrophosphate (TPP)

The active coenzyme form of vitamin $B_1$ (thiamin), synthesized in the liver from thiamin, that catalyzes decarboxylation reactions in energy pathways and two-carbon transfers.

Transketolase

A thiamin-dependent enzyme in the non-oxidative branch of the pentose phosphate pathway that transfers two-carbon units to produce $NADPH$ and ribose-5-phosphate for nucleotide synthesis.

Dry Beriberi

A chronic deficiency state of vitamin $B_1$ (thiamin) characterized primarily by neurological impairment, muscle wasting, peripheral neuropathy, loss of tendon reflexes, and foot or wrist drop.

Wet Beriberi

A manifestation of thiamin (vitamin $B_1$) deficiency characterized predominantly by cardiovascular symptoms, including congestive heart failure and peripheral edema.

Infantile Beriberi

An acute thiamin deficiency seen in breastfed infants (typically by age $3$ to $4\,\text{weeks}$) of thiamin-deficient mothers, presenting with sudden heart failure, aphonia, and absent deep tendon reflexes.

Flavin Adenine Dinucleotide (FAD)

A major redox coenzyme synthesized from riboflavin (vitamin $B_2$) that accepts and donates electrons in carbohydrate, fatty acid, and protein catabolism and the citric acid cycle.

Glutathione Reductase

A riboflavin-dependent ($FAD$-requiring) antioxidant enzyme that converts oxidized glutathione ($GSSG$) back to reduced glutathione ($2\,\text{GSH}$) using reducing equivalents from $NADPH$.

Corn Nixtamalization

The traditional practice of soaking corn in alkaline water to break the tight chemical bonds holding niacin to proteins, thereby increasing the bioavailability of niacin for absorption.

Pellagra

A deficiency disease caused by a severe lack of dietary niacin (vitamin $B_3$), characterized by Casal's necklace and the "4 Ds": dermatitis, diarrhea, dementia, and death.

Coenzyme A (CoA)

A critical metabolic cofactor derived from pantothenic acid (vitamin $B_5$) that binds acyl groups via a terminal sulfhydryl group to form high-energy intermediates like acetyl-CoA.

Biocytin

The dietary bound form of biotin attached covalently to a lysine residue within food proteins, which must be hydrolyzed by intestinal biotinidase prior to absorption.

Avidin

A protein present in raw egg whites that binds dietary biotin with high affinity, preventing its intestinal absorption and precipitating biotin deficiency if consumed raw in large quantities.

Chromium ($Cr^{3+}$)

An inorganic trace mineral that binds to transferrin in blood and enhances insulin action to help normalize cellular uptake of blood glucose.

Free Radical

An unstable, highly reactive chemical species possessing an unpaired electron in its outer orbital that can induce damaging chain reactions in cellular lipids, proteins, and $DNA$.

Prolyl and Lysyl Hydroxylation

Vitamin $C$-dependent post-translational enzymatic reactions that hydroxylate proline and lysine residues in procollagen, enabling cross-linking to form a stable collagen triple helix.

Scurvy

A fatal connective tissue disease resulting from severe vitamin $C$ deficiency, caused by impaired collagen synthesis and marked by capillary fragility, bleeding gums, and poor wound healing.

$\alpha$-Tocopherol

The most biologically active vitamer of fat-soluble vitamin $E$, which resides within phospholipid cell membranes and donates electrons to quench free radicals, preventing lipid peroxidation.

Hemolytic Anemia

A condition characterized by the premature destruction and rupturing (hemolysis) of red blood cell membranes, which can occur secondary to vitamin $E$ deficiency due to unchecked lipid peroxidation.

Selenocysteine

A specialized amino acid containing selenium in place of sulfur that is incorporated directly into antioxidant selenoproteins, such as glutathione peroxidase.

Glutathione Peroxidase

A selenium-dependent antioxidant enzyme that detoxifies reactive hydrogen peroxide ($H_2O_2$) into water ($2\,H_2O$) while converting reduced glutathione ($2\,\text{GSH}$) to oxidized glutathione ($GSSG$).

Retinoic Acid

A vitamer form of vitamin $A$ that acts as a transcription-regulating hormone by binding nuclear receptors to govern gene expression, cell differentiation, proliferation, and mucosal secretion.

Rhodopsin

The light-sensitive visual photopigment in retinal rod cells composed of the opsin protein bound to $11\text{-cis-retinal}$, which isomerizes to $\text{all-trans-retinal}$ upon exposure to light.

Bitot's Spots

Superficial foamy, triangular patches of keratin debris that form on the conjunctiva of the eye, presenting as an early ocular sign of vitamin $A$ deficiency.

Keratomalacia

Severe, irreversible corneal softening, ulceration, and opacity caused by advanced, chronic vitamin $A$ deficiency, resulting in permanent blindness.

Anemia

A clinical condition characterized by a reduced total number of red blood cells or decreased hemoglobin concentration, compromising oxygen delivery to peripheral tissues.

Heme Iron

Ferrous iron ($Fe^{2+}$) bound inside a porphyrin ring found in meat, poultry, and fish, which is absorbed with high efficiency ($\sim 25\%$) and minimally affected by dietary factors.

Non-Heme Iron

Elemental iron, predominantly ferric ($Fe^{3+}$), found in plant foods, enriched grains, and cookware, which exhibits lower bioavailability ($\sim 10\%$) and is strongly influenced by dietary enhancers and inhibitors.

Mucosal Block

The regulatory mechanism by which the intestine prevents iron toxicity by storing unneeded iron in enterocyte ferritin, which is subsequently excreted when the mucosal lining sloughs off into feces.

Hephaestin

A copper-dependent ferroxidase enzyme on the enterocyte basolateral membrane that oxidizes exported ferrous iron ($Fe^{2+}$) to ferric iron ($Fe^{3+}$) so it can bind to serum transferrin.

Microcytic Hypochromic Anemia

A hematologic disorder defined by abnormally small (microcytic) and pale (hypochromic) erythrocytes, resulting from impaired hemoglobin synthesis due to severe iron deficiency or vitamin $B_6$ deficiency.

Pyridoxal Phosphate (PLP)

The principal active coenzyme form of vitamin $B_6$, converted in the liver and transported on albumin, required for amino acid transamination and decarboxylation, and the initial step of heme synthesis.

Folate Conjugase

An intestinal brush border enzyme that cleaves extra glutamate residues from dietary folate polyglutamate, yielding the absorbable monoglutamate form.

Megaloblastic (Macrocytic) Anemia

A form of anemia caused by folate or vitamin $B_{12}$ deficiency characterized by enlarged, immature red blood cell precursors arrested in bone marrow with retained nuclei due to impaired $DNA$ synthesis.

Neural Tube Defects

Severe congenital malformations, including spina bifida and anencephaly, caused by failure of the embryonic neural tube to close during early gestation due to maternal folate deficiency.

Intrinsic Factor

A glycoprotein secreted by gastric parietal cells that binds cobalamin (vitamin $B_{12}$) in the small intestine to permit receptor-mediated endocytosis in the terminal ileum.

Methylmalonyl-CoA Mutase

A vitamin $B_{12}$-dependent enzyme that converts methylmalonyl-CoA to succinyl-CoA during the catabolism of odd-chain fatty acids and branched-chain amino acids, vital for central nervous system myelin integrity.