Biochemistry: Carbohydrates, Metabolism, and Clinical Diagnostics

Comprehensive vocabulary flashcards covering carbohydrate structure, stereochemistry, isomerism, analytical reactions, polysaccharides, amino acid metabolism, clinical enzyme deficiencies, and protein architecture from the lecture notes.

AST and ALT

Aspartate aminotransferase and alanine aminotransferase; intracellular hepatic enzymes that leak into the bloodstream during hepatocellular damage and share the metabolic mechanism of converting $\alpha$-ketoglutarate to glutamate via transamination.

Argininosuccinate Synthetase Deficiency

A severe urea cycle defect presenting within $24\,\text{hours}$ of birth with lethargy, hypothermia, apnea, hyperammonemia, low blood urea levels, and marked accumulation of citrulline in the blood.

Maple Syrup Urine Disease

An inborn error of metabolism caused by a deficiency in critical enzymes responsible for the catabolism of branched-chain amino acids, presenting in neonates with vomiting, lethargy, poor suckling behavior, and progressive decerebrate posturing.

Lead-Induced Heme Biosynthesis Inhibition

The toxic inactivation of the enzymes $\delta$-aminolevulinic acid (ALA) dehydratase and ferrochelatase in the heme pathway by elevated blood lead levels, resulting in failure to thrive, anemia, and elevated excretion of coproporphyrinogen III in the urine.

Isoniazid-Induced Pyridoxine Deficiency

A drug-induced nutritional deficiency occurring during prophylactic tuberculosis treatment where vitamin $B_6$ is depleted, causing peripheral neuropathy and predominantly impairing cellular amino acid metabolism.

Tyrosine

An aromatic amino acid whose defective enzymatic metabolism causes albinism (characterized by white skin, white hair, and nystagmus); it serves as a critical biosynthetic precursor for melanin, dopamine, and norepinephrine.

Carbohydrates

Naturally occurring polyhydroxy aldehydes (aldoses), polyhydroxy ketones (ketoses), and their derivatives, exhibiting the general empirical formula $(CH_2O)_n$ where $n \ge 3$, and supplying approximately $4\,\text{kcal/g}$ of accessible metabolic energy.

Asymmetric Carbon

A chiral carbon atom bonded to four chemically distinct groups that confers optical activity, allowing a sugar to turn the plane of plane-polarized light.

Stereoisomer Formula ($2^n$)

A mathematical rule stating that the maximum number of possible stereoisomers for an open-chain sugar is given by $2^n$, where $n$ represents the number of asymmetric chiral carbon atoms.

Enantiomers

Stereoisomers that are non-superimposable mirror images of each other, designated as D- and L-sugars, which have identical chemical properties in achiral environments but rotate plane-polarized light in equal and opposite directions.

Racemic Mixture

An equimolar mixture containing equal proportions of D- and L-enantiomers that exhibits zero net optical rotation due to mutual cancellation.

Epimers

Diastereomers that differ in their three-dimensional spatial configuration around only one specific chiral center, such as D-glucose and D-mannose at $C_2$, or D-glucose and D-galactose at $C_4$.

Anomers

Isomeric cyclic forms of monosaccharides that differ only in spatial configuration about the carbonyl carbon (designated the anomeric carbon: $C_1$ in aldoses, $C_2$ in ketoses), forming $\alpha$ and $\beta$ configurations.

Mutarotation

The progressive change in optical rotation over time when pure anomers of a cyclic sugar dissolve in water until reaching thermodynamic equilibrium (e.g., pure $\alpha\text{-D-glucose}$ shifting from $+112^\circ$ and pure $\beta\text{-D-glucose}$ from $+18.7^\circ$ to an equilibrium angle of $+52.7^\circ$).

Pyranose Ring

A six-membered cyclic ring containing five carbon atoms and one oxygen atom, formed by intramolecular hemiacetal or hemiketal condensation between a carbonyl group and a hydroxyl group (e.g., $C_5\text{-OH}$ of glucose).

Furanose Ring

A five-membered cyclic ring containing four carbon atoms and one oxygen atom, formed through intramolecular condensation of a hydroxyl group with a carbonyl carbon.

Kiliani Synthesis

A chemical chain-elongation reaction that converts an aldose into a homologous aldose containing one additional carbon atom by treatment with hydrogen cyanide ($HCN$), followed by hydration to a carboxylic acid and reduction with sodium amalgam ($Na/Hg$).

Bial's Test

A diagnostic chemical test using orcinol and ferric chloride in concentrated hydrochloric acid that rapidly converts pentoses to furfurals to produce a characteristic green color, while hexoses react more slowly to yield a pink color.

Seliwanoff's Test

A colorimetric chemical test used to differentiate ketoses from aldoses based on the rapid acid-catalyzed dehydration of ketoses to form furfurals that react with resorcinol to give a deep red or pink color.

Barfoed's Test

A copper-reduction test using cupric acetate in weak acetic acid that differentiates monosaccharides from disaccharides; monosaccharides produce a red-brown precipitate within $30\,\text{seconds}$, whereas disaccharides require $1\text{--}2\,\text{minutes}$.

Enediol Intermediate

An enolic tautomeric intermediate formed at room temperature when monosaccharides are treated with dilute alkali, facilitating the interconversion of glucose, fructose, and mannose via rearrangement about $C_1$ and $C_2$.

Maltose

A reducing disaccharide composed of two $\alpha\text{-D-glucose}$ units linked by an $\alpha\text{-(1}\rightarrow\text{4)}$ glycosidic bond, produced as an intermediate during the enzymatic digestion of starch by amylase.

Lactose

A reducing disaccharide synthesized in the mammary gland and present in milk, consisting of $\beta\text{-D-galactose}$ joined to $\beta\text{-D-glucose}$ by a $\beta\text{-(1}\rightarrow\text{4)}$ glycosidic linkage.

Sucrose

A non-reducing disaccharide common in cane and beet sugar composed of $\alpha\text{-D-glucopyranose}$ and $\beta\text{-D-fructofuranose}$ joined through their respective anomeric carbons via an $\alpha\text{-(1}\rightarrow\text{2)}$ glycosidic bond.

Cellobiose

A repeating disaccharide unit produced by the partial hydrolysis of cellulose, composed of two D-glucose molecules joined by a $\beta\text{-(1}\rightarrow\text{4)}$ glycosidic linkage.

Trehalose

A non-reducing disaccharide composed of two $\alpha\text{-D-glucose}$ molecules joined via an $\alpha\text{-(1}\rightarrow\text{1)}$ glycosidic bond, serving as the principal circulating sugar in insect hemolymph as well as fungi and yeasts.

Raffinose

A plant oligosaccharide (trisaccharide) found in sugar beets composed of $\alpha\text{-D-galactose}$, $\alpha\text{-D-glucose}$, and $\beta\text{-D-fructose}$ linked together.

Amylose

The linear, unbranched homopolysaccharide component of starch ($15\text{--}20\%$ by weight) composed of $\alpha\text{-D-glucose}$ units connected by $\alpha\text{-(1}\rightarrow\text{4)}$ glycosidic bonds that adopts a helical coil and stains blue with iodine.

Amylopectin

The major branched homopolysaccharide component of starch ($80\text{--}85\%$ by weight) composed of $\alpha\text{-(1}\rightarrow\text{4)}$ glucose backbones with $\alpha\text{-(1}\rightarrow\text{6)}$ branch points occurring every $25\text{--}30$ glucose residues, reacting with iodine to yield a pink-red color.

Glycogen

The major storage homopolysaccharide in animals, comprising up to $10\%$ of liver dry weight and $1\text{--}2\%$ of skeletal muscle, composed of $\alpha\text{-D-glucose}$ chains joined by $\alpha\text{-(1}\rightarrow\text{4)}$ bonds with frequent $\alpha\text{-(1}\rightarrow\text{6)}$ branches occurring every $12\text{--}18$ to $25\text{--}30$ residues.

Dextrans

Bacterial and yeast storage polysaccharides consisting of $\alpha\text{-D-glucose}$ units joined principally by $\alpha\text{-(1}\rightarrow\text{6)}$ glycosidic bonds, featuring branch points at $\alpha\text{-(1}\rightarrow\text{3)}$ or $\alpha\text{-(1}\rightarrow\text{4)}$ positions.

Cellulose

An unbranched structural homopolysaccharide in plant cell walls composed of linear chains of D-glucose monomers connected by $\beta\text{-(1}\rightarrow\text{4)}$ glycosidic bonds.

Hyaluronic Acid

An unbranched glycosaminoglycan (heteropolysaccharide) found in extracellular matrices and connective tissues, composed of alternating repeating disaccharide units of $\beta\text{-D-glucuronic acid}$ and $N\text{-acetylglucosamine}$.

Heparin

A highly sulfated glycosaminoglycan produced by mast cells that functions as an anticoagulant, composed of repeating disaccharides of sulfated D-glucosamine and sulfated iduronic acid.

D-Lyxose

An aldopentose found as a specialized constituent of lyxoflavin, a compound isolated from human heart muscle.

L-Xylulose

A pentose intermediate formed in the uronic acid pathway that is excreted in the urine of individuals affected by the benign metabolic anomaly essential pentosuria.

Glycoproteins

Conjugated proteins bearing covalently linked branched or unbranched oligosaccharide chains, serving as structural proteins (collagen), plasma proteins (fibrinogen, immunoglobulins), hormones (FSH, TSH), and cell surface antigens.

Standard Alpha-Helix

A prominent regular secondary structural motif in proteins stabilized by intrachain hydrogen bonds between the carbonyl oxygen ($C=O$) of residue $n$ and the peptide amide nitrogen ($N-H$) of residue $n+4$.

Nucleoside vs. Nucleotide

A nucleoside is a molecular unit consisting of a purine or pyrimidine base linked covalently to a pentose sugar (ribose or deoxyribose), whereas a nucleotide is a nucleoside possessing one or more esterified phosphate groups.

Substrate-Level Phosphorylation

The direct metabolic synthesis of ATP or GTP through the enzymatic transfer of a high-energy phosphate group from an activated, phosphorylated intermediate directly to ADP or GDP, operating independently of the mitochondrial electron transport chain.

Oxidative Phosphorylation

The process occurring in the inner mitochondrial membrane where energy released from transferring electrons through respiratory complexes to oxygen is coupled to the trans-membrane pumping of protons, which drives ATP synthesis via ATP synthase.

Ubiquitin-Proteasome Pathway

An ATP-dependent protein degradation system wherein target proteins are tagged covalently with a polyubiquitin chain through an enzymatic cascade and subsequently degraded into peptide fragments within the $26S$ proteasome complex.