Aspects of Biochemistry: Carbohydrates (Disaccharides)

Vocabulary practice flashcards covering disaccharide types, structural characteristics, formation and breakdown reactions, chemical reactivity, and laboratory testing procedures.

Disaccharide

A carbohydrate composed of two simple sugars joined together that is sweet-tasting and soluble in water.

Maltose

A reducing disaccharide formed from two glucose molecules that is commonly used in brewing.

Lactose

A reducing disaccharide composed of glucose and galactose that serves as the transport sugar in milk.

Sucrose

The most widely occurring disaccharide, composed of glucose and fructose with the molecular formula $C_{12}H_{22}O_{11}$, also known as table sugar, cane sugar, or beet sugar.

Condensation reaction

A chemical reaction that forms a glycosidic bond between monosaccharide units through the removal of a molecule of water ($H_2O$).

Hydrolysis reaction

A chemical reaction that breaks a glycosidic bond between sugars through the addition of a molecule of water ($H_2O$).

1,2-Glycosidic bond

The covalent linkage formed in sucrose between carbon-1 ($C_1$) of $\alpha\text{-D-glucose}$ and carbon-2 ($C_2$) of $\beta\text{-D-fructose}$.

Sucrase

The enzyme in the small intestine responsible for hydrolyzing sucrose into its constituent monosaccharides, glucose and fructose.

Non-reducing sugar

A sugar, such as sucrose, that lacks a free hemiacetal functional group because its anomeric carbons are involved in a glycosidic linkage, leaving it locked in cyclic form and unable to reduce Benedict's reagent.

Hemiacetal group

A functional group present in reducing sugars like maltose and lactose that allows the sugar ring to open into an reactive aldehyde or ketone form to yield a positive Benedict's test.

Test for non-reducing sugars

A procedure where a sample is first confirmed negative with Benedict's reagent, boiled in a water bath for 5 minutes with dilute hydrochloric acid to hydrolyze it, neutralized with sodium hydrogen carbonate, cooled, and re-tested with Benedict's reagent to produce a color change.

Semi-quantitative Benedict's test

An assay that estimates approximate reducing sugar concentration via distinct precipitate colors: blue (none), green (trace / very low), yellow (low), brown / orange-red (medium / moderate), and red / brick-red (high / large amount).

Haworth projection

A standard cyclic structural representation of a cyclic sugar, such as the furanose ring form of fructose derived from its open-chain Fischer projection.

Phloem transport

The vascular transport mechanism in plants that carries sucrose, utilizing its high water solubility and relative chemical unreactivity to move sugar throughout the plant.