Carbohydrates: Structure, Properties, and Classification

Vocabulary practice flashcards covering carbohydrate structure, stereochemistry, monosaccharide derivatives, chemical reactions, disaccharides, and polysaccharides from the Medical Faculty Chemistry lecture.

Carbohydrates

Polyhydroxyl aldoses or polyhydroxyl ketoses, as well as substances whose hydrolysis yields these compounds, commonly having the empirical formula $(CH_2O)_n$.

Monosaccharides

Simple sugars containing three to nine carbon atoms that cannot be broken down into simpler carbohydrate compounds by hydrolysis with dilute mineral acids.

Chiral (Asymmetric) Carbon Atom

A carbon atom bonded to four entirely different atoms or functional groups.

Dioxyacetone

A ketotriose with three carbon atoms that is the only monosaccharide lacking a chiral carbon atom.

Enantiomers

Stereoisomers that are non-superimposable mirror images of each other, designated as D- and L-forms based on absolute configuration (exemplified by glyceraldehyde).

Stereoisomer Formula ($X = 2^n$)

A mathematical relationship where the total number of stereoisomers ($X$) equals $2^n$, with $n$ representing the number of chiral carbon atoms.

Epimerism

A form of diastereoisomerism in which two isomers differ in spatial configuration at only one of their chiral carbon atoms (e.g., D-glucose is a C-2 epimer of D-mannose and a C-4 epimer of D-galactose).

Anomers

Diastereoisomers produced during cyclic hemiacetal or hemiketal formation that differ in configuration exclusively at the new chiral center (the anomeric carbon).

Pyranose

A six-membered cyclic hemiacetal form of a sugar, such as $\alpha$-D-glucopyranose, formed by intramolecular reaction between the carbonyl group and the hydroxyl group at C-5.

Furanose

A five-membered cyclic hemiketal form of a sugar derived from tetrahydrofuran, such as $\alpha$- and $\beta$-D-fructofuranose, formed by intramolecular cyclization involving the keto group and C-5 hydroxyl.

Haworth Projection

A graphic representation of cyclic sugar structures where the ring is depicted in a plane with ring oxygen and carbons, while hydrogen atoms and hydroxyl groups extend above or below the plane.

Mutarotation

The progressive change in optical rotation of a freshly dissolved anomer solution until equilibrium is reached at $+52.5^\circ$, resulting from the interconversion between $\alpha$ and $\beta$ forms in a $36:64$ ratio.

Alditols

Polyhydroxyl sugar alcohols obtained by the reduction of the carbonyl group of monosaccharides using reducing agents such as $H_2$ or $NaBH_4$ (e.g., sorbitol, mannitol, and ribitol).

Aldonic Acids

Monocarboxylic sugar acids produced by selective oxidation of the aldehyde group of an aldose, such as gluconic acid formed using $Br_2/H_2O$.

Uronic Acids

Monosaccharide derivatives formed by selective oxidation of the terminal primary alcohol group at C-6 (e.g., glucuronic acid), crucial for detoxifying and conjugating substances like salicylic acid for urinary excretion.

Aldaric Acids

Dicarboxylic sugar acids formed by strong oxidation of both the aldehyde group and the terminal primary alcohol group using agents such as $HNO_3$ (e.g., glucaric acid).

Osazones

Yellow, water-insoluble crystalline derivatives formed by the reaction of reducing monosaccharides with phenylhydrazine, utilized for identifying sugars.

Glycosides

Cyclic acetals or ketals formed by reacting the cyclic hemiacetal or hemiketal form of a monosaccharide with alcohols or phenols in the presence of an acid catalyst.

Maltose

A reducing disaccharide produced by amylase hydrolysis of amylose, consisting of two D-glucose units linked by an $\alpha-(1\rightarrow 4')$ glycosidic bond.

Cellobiose

A disaccharide composed of two glucose molecules joined by a $\beta-(1\rightarrow 4')$ glycosidic bond, acting as the fundamental structural unit of cellulose.

Lactose

A reducing disaccharide (milk sugar) consisting of D-galactose and D-glucose linked by a $\beta-(1\rightarrow 4')$ glycosidic bond, hydrolyzed in humans by the enzyme lactase.

Sucrose

A non-reducing disaccharide composed of D-glucose and D-fructose linked head-to-head via both hemiacetal hydroxyl groups ($1\alpha \rightarrow 2\beta$), exhibiting no mutarotation or osazone formation.

Cellulose

A linear homopolysaccharide of $2,500$ to $12,000$ D-glucose units joined by $\beta-(1\rightarrow 4')$ glycosidic bonds that serves as the primary structural component of plant cell walls.

Amylose

A linear, water-soluble starch fraction consisting of $200$ to $350$ D-glucose units linked exclusively by $\alpha-(1\rightarrow 4)$ glycosidic bonds.

Amylopectin

The branched component of starch composed of D-glucose chains linked by $\alpha-(1\rightarrow 4)$ bonds with branch points formed by $\alpha-(1\rightarrow 6)$ glycosidic bonds.

Hyaluronic Acid

A high-molecular-weight glycosaminoglycan polymer consisting of alternating D-glucuronic acid and N-acetylglucosamine units linked by $\beta-(1\rightarrow 3)$ and $\beta-(1\rightarrow 4)$ bonds, functioning as a joint lubricant and tissue barrier.

Chondroitin-Sulfate

A structural glycosaminoglycan present in cartilage, skin, and bone tissue, composed of repeating disaccharide units of D-glucuronic acid and N-acetylgalactosamine linked by $\beta-(1\rightarrow 3)$ and $\beta-(1\rightarrow 4)$ bonds.

Glycoproteins

Heteropolysaccharide conjugates containing a polypeptide backbone covalently linked via O-glycosidic bonds (to serine or threonine) or N-glycosidic bonds (to asparagine) to branched oligosaccharide chains.