Water-Soluble Vitamins: B-Complex (Biochemical Aspects)

Vocabulary practice flashcards covering the biochemical forms, physiological functions, activation pathways, coenzymes, and clinical deficiency syndromes of water-soluble B-complex vitamins (B1, B2, B3, B6, and B12).

Thiamin (Vitamin $B_1$)

The first water-soluble B-complex vitamin discovered; it is predominantly concentrated in skeletal muscles due to its central role in cellular energy production.

Thiamin Diphosphotransferase

The specific enzyme located in the brain and liver that rapidly phosphorylates absorbed thiamin into its metabolically active coenzyme form, thiamin pyrophosphate (TPP).

Thiamin Pyrophosphate (TPP)

The active coenzyme form of vitamin $B_1$ that mediates oxidative decarboxylation reactions in carbohydrate metabolism (glycolysis and the Krebs cycle) to generate biological energy.

Beri Beri

A severe nutritional disease resulting from a diet high in carbohydrates and deficient in thiamin ($B_1$), manifesting as ataxia, fatigue, depression, muscle weakness, and cardiovascular and nervous system dysfunction.

Riboflavin (Vitamin $B_2$)

A water-soluble vitamin stored primarily in the liver, kidney, and heart (with $70\text{--}90\%$ stored as FAD or FMN), serving as the precursor for active flavin coenzymes.

Flavin Adenine Dinucleotide (FAD) & Flavin Mononucleotide (FMN)

The active phosphorylated coenzyme forms of riboflavin that participate as electron carriers in roughly 150 biological oxidation-reduction reactions involved in energy production and macronutrient metabolism.

Riboflavin Deficiency

A nutritional deficiency state characterized by burning, itching, tearing, and bloodshot eyes, dermatitis, oily skin, and oral lesions such as stomatitis and mouth ulcers.

Nicotinic Acid (Niacin)

A dietary form of vitamin $B_3$ found in foods such as meat, fish, eggs, and wheat flour; it can also be endogenously synthesized in the liver from the amino acid tryptophan.

Nicotinamide (Niacinamide)

The amide form of vitamin $B_3$ found in foods that functions alongside nicotinic acid as a vital component of cellular pyridine nucleotide coenzymes.

$NAD^+$ / $NADH$

The nicotinamide-containing coenzymes responsible for catabolic oxidation-reduction reactions, functioning with dehydrogenase enzymes and the electron transport system for ATP generation.

$$NADPH$$

The phosphorylated nicotinamide coenzyme that provides reducing equivalents for anabolic biosynthetic pathways, including fatty acid, cholesterol, and purine/pyrimidine synthesis.

Pellagra

A severe vitamin $B_3$ (niacin) deficiency disorder classically presenting with the triad of dermatitis (skin inflammation), diarrhea (malabsorption), and dementia (mental disorientation and impaired cognition).

Pyridoxine (Vitamin $B_6$)

A water-soluble B vitamin found in poultry, fish, bananas, oats, and legumes that serves as an enzymatic cofactor participating in over 100 metabolic reactions.

Pyridoxal Phosphate (PLP)

The active coenzyme form of vitamin $B_6$ that acts as a cofactor for aromatic amino acid decarboxylase in condensation, transamination, and the biosynthesis of hemoglobin and neurotransmitters.

Vitamin $B_6$ Deficiency

A deficiency syndrome presenting with symptoms such as loss of appetite, nausea, apathy, drowsiness, dry skin around the eyes, focal hair loss, sores in the corners of the mouth, and kidney stones.

Cobalamin (Vitamin $B_{12}$)

A family of cobalt-containing water-soluble compounds that are stored in the liver in amounts of $2\text{--}5\,\text{mg}$ (about $90\%$ of total body stores, lasting up to 2 years) and are vital for RBC production and nerve sheath maintenance.

Intrinsic Factor (IF)

A gastric glycoprotein secreted by parietal cells of the stomach that binds free vitamin $B_{12}$ after gastric $HCl$ cleaves it from dietary proteins, enabling absorption in the ileum.

Pernicious Anemia

A megaloblastic anemia caused by intrinsic factor deficiency leading to vitamin $B_{12}$ malabsorption; clinically marked by neuropathy, fatigue, weakness, dyspnea, impaired concentration, and peripheral nerve damage.