Carbohydrates: Sugars and Polysaccharides

Comprehensive vocabulary flashcards covering the classification, stereochemistry, ring cyclization, derivatives, disaccharides, and polysaccharides from the lecture notes.

Monosaccharides

The basic units of carbohydrates (simple sugars), consisting of aldehydes or ketones with two or more hydroxyl groups and an empirical formula of $(CH_2O)_n$, where $n \ge 3$.

Aldose

A monosaccharide containing an aldehyde functional group, such as glyceraldehyde or glucose.

Ketose

A monosaccharide containing a ketone functional group, such as dihydroxyacetone or fructose, having one less asymmetric center than its isomeric aldose counterpart.

D- and L-Sugars

Stereoisomeric designations for monosaccharides based on the absolute configuration at the asymmetric carbon center farthest from the carbonyl group, referenced to D-glyceraldehyde; L-sugars are mirror images of D-sugars.

Epimers

Sugars that differ in stereochemical configuration around only one carbon atom, such as D-glucose and D-mannose at C-2, or D-glucose and D-galactose at C-4.

Hemiacetal

The product formed by the reversible reaction of an alcohol with the carbonyl group of an aldehyde, forming an intramolecular cyclic ring in aldose sugars.

Hemiketal

The product formed by the reversible nucleophilic addition of an alcohol hydroxyl group to the carbonyl group of a ketone.

Anomeric Carbon

The carbonyl carbon atom (C-1 in aldoses or C-2 in ketoses) that becomes a new asymmetric stereocenter upon ring closure to form a cyclic hemiacetal or hemiketal.

Anomers

Isomeric cyclic forms of a sugar (designated $\alpha$ and $\beta$) that differ only in configuration at the anomeric carbon.

Mutarotation

The spontaneous conversion between $\alpha$ and $\beta$ anomeric forms of a monosaccharide in aqueous solution until an equilibrium mixture is reached.

Pyranose

A cyclic monosaccharide containing a six-membered hemiacetal or hemiketal ring structure.

Furanose

A cyclic monosaccharide containing a five-membered hemiacetal or hemiketal ring structure.

Haworth Projections

Structural formulas that unambiguously depict the stereoconfiguration and spatial ring relationships of cyclic monosaccharides.

Chair Conformation

The predominant and most stable nonplanar pyranose ring conformation with $109^\circ$ bond angles, which is approximately $25\,kJ\,mol^{-1}$ more stable than the boat conformation due to reduced steric crowding and eclipsing strain.

$\beta$-D-Glucose

The only D-aldohexose that can simultaneously position all five of its non-hydrogen substituents in equatorial orientations, making it the most abundant form ($62\%$) in water at $25^\circ\text{C}$.

Reducing Sugar

An aldose or ketose possessing a free or accessible anomeric carbon that can reduce mild oxidizing reagents such as Tollen's reagent or Fehling's solution.

Tollen's Reagent

An ammonium sulfate solution containing $Ag^+$ used to detect reducing sugars; its reduction results in the deposition of a metallic silver mirror.

Fehling's Solution

An alkaline reagent containing cupric ions ($Cu^{2+}$) that reacts with reducing sugars to form a characteristic red cuprous oxide ($Cu_2O$) precipitate.

Aldonic Acid

A sugar acid produced by mild chemical or enzymatic oxidation of an aldose aldehyde group (C-1) to a carboxylic acid (e.g., D-gluconic acid), which exists in equilibrium with lactones.

Uronic Acid

A sugar acid produced by the specific oxidation of the primary alcohol group (C-6) of an aldose to a carboxylic acid, such as D-glucuronic acid, D-galacturonic acid, or D-mannuronic acid.

Aldaric Acid

A dicarboxylic sugar acid formed by oxidation of both the C-1 aldehyde group and the C-6 primary alcohol group of an aldose, such as D-glucaric acid.

Alditols

Sugar alcohols formed by mild reduction of the carbonyl group of aldoses or ketoses with $NaBH_4$; they cannot cyclize and are commonly used as artificial sweeteners (e.g., sorbitol, mannitol, xylitol).

Deoxy Sugars

Monosaccharides that have one or more hydroxyl groups replaced by hydrogen atoms, such as 2-deoxyribose in DNA, $\alpha$-L-rhamnose, and $\alpha$-L-fucose.

Amino Sugars

Monosaccharide derivatives in which one or more hydroxyl groups are replaced by amino groups, such as D-glucosamine and D-galactosamine.

N-Acetylmuramic Acid (NAM)

An amino sugar derivative formed from N-acetyl-D-glucosamine linked by an ether bond to D-lactic acid, forming a prominent repeating component of bacterial cell walls.

Glycosidic Bond

The covalent acetal or ketal linkage formed between the anomeric carbon of a cyclic sugar and the hydroxyl oxygen of an alcohol or another monosaccharide residue.

Disaccharides

Oligosaccharides composed of two monomeric monosaccharide residues linked together by a glycosidic bond.

Maltose

A reducing homodisaccharide produced from starch hydrolysis consisting of two D-glucose residues connected by an $\alpha(1\rightarrow 4)$ glycosidic bond ($\text{Glc}\alpha1\text{-}4\text{Glc}$).

Cellobiose

A reducing homodisaccharide breakdown product of cellulose composed of two D-glucose residues joined by a $\beta(1\rightarrow 4)$ glycosidic bond ($\text{Glc}\beta1\text{-}4\text{Glc}$).

Lactose

A reducing disaccharide that serves as the principal carbohydrate in milk, composed of D-galactose and D-glucose linked by a $\beta(1\rightarrow 4)$ glycosidic bond, hydrolyzed by lactase.

Sucrose

A nonreducing disaccharide (table sugar) composed of glucose and fructose linked via both anomeric carbons ($\text{Glc}\alpha(1\rightarrow 2)\beta\text{Fru}$), hydrolyzed by invertase or sucrase.

Cellulose

A rigid, water-insoluble structural polysaccharide of plant cell walls consisting of up to $15{,}000$ D-glucose units linked by $\beta(1\rightarrow 4)$ glycosidic bonds that form parallel, hydrogen-bonded sheets.

Cellulase

A group of enzymes secreted by symbiotic microorganisms in herbivores and termites capable of hydrolyzing the $\beta(1\rightarrow 4)$ glycosidic bonds of cellulose.

Chitin

A structural homopolysaccharide composed of $\beta(1\rightarrow 4)$-linked N-acetyl-D-glucosamine (NAG) units found in invertebrate exoskeletons and the cell walls of fungi and algae.

Starch

The primary calorie reserve of plants stored as insoluble cytoplasmic granules, composed of linear $\alpha$-amylose ($10\text{--}30\%$) and branched amylopectin ($70\text{--}90\%$).

$\alpha$-Amylose

A linear plant starch polymer of several thousand D-glucose units linked by $\alpha(1\rightarrow 4)$ glycosidic bonds that forms a left-handed helix with 6 residues per turn and a pitch of $8\,\text{Å}$.

Amylopectin

A branched plant starch component consisting of $\alpha(1\rightarrow 4)$-linked glucose chains with $\alpha(1\rightarrow 6)$ branch points occurring every 24 to 30 residues, containing up to $10^6$ glucose units.

Glycogen

The primary storage polysaccharide in animals found as granules in muscle and liver, consisting of $\alpha(1\rightarrow 4)$-linked glucose chains with $\alpha(1\rightarrow 6)$ branches every 8 to 12 residues.

Glycogen Phosphorylase

The enzyme that mobilizes cellular glycogen by phosphorolytically cleaving $\alpha(1\rightarrow 4)$ glycosidic bonds sequentially from nonreducing ends to yield glucose-1-phosphate.