Carbohydrates: Monosaccharides, Disaccharides, and Polysaccharides

Vocabulary flashcards covering the structure, properties, and testing of carbohydrates including monosaccharides, disaccharides, and polysaccharides such as starch, glycogen, and cellulose.

Carbohydrates

Organic molecules with the general formula $C_n(H_2O)_m$.

Monosaccharides

Simple sugars with the general formula $(CH_2O)_n$ that contain a free carbonyl $(C=O)$ group and multiple hydroxyl $(OH)$ groups.

Reducing Sugars

Sugars that possess a free carbonyl $(C=O)$ group; examples include all monosaccharides and all disaccharides except sucrose.

$\alpha$-glucose

An isomer of glucose where the hydroxyl $(OH)$ group at $C1$ is below the ring and on the opposite side of $C6$. Alone or in chains, all monomers have the same orientation.

$\beta$-glucose

An isomer of glucose where the hydroxyl $(OH)$ group at $C1$ is above the ring and on the same side as $C6$. In polymers, alternate monomers must be rotated $180^{\circ}$.

Glycosidic bond

A covalent bond formed between two monosaccharides through a condensation reaction involving the loss of a water molecule.

Hydrolysis reaction

A process where a glycosidic bond is broken with the addition of one molecule of water, splitting a disaccharide or polysaccharide into monosaccharides.

Sucrose

A non-reducing disaccharide formed from the condensation of glucose and fructose.

Maltose

A reducing disaccharide formed from the condensation of two glucose monomers.

Lactose

A reducing disaccharide formed from the condensation of glucose and galactose.

Polysaccharides

Large molecules with the general formula $(C_6H_{10}O_5)_n$ made up of many monosaccharides joined by glycosidic bonds.

Amylose

An unbranched, helical component of starch consisting of $\alpha$-glucose monomers linked by $\alpha(1-4)$ glycosidic bonds.

Amylopectin

A branched, helical component of starch consisting of $\alpha$-glucose monomers linked by $\alpha(1-4)$ glycosidic bonds with $\alpha(1-6)$ glycosidic bonds at branch points.

Glycogen

An extensively branched animal storage polysaccharide located in liver and muscle cells, made of $\alpha$-glucose monomers linked by $\alpha(1-4)$ and $\alpha(1-6)$ glycosidic bonds.

Cellulose

A plant structural polysaccharide made of $\beta$-glucose monomers linked by $\beta(1-4)$ glycosidic bonds, forming long, straight chains.

Microfibrils

Bundles of parallel cellulose chains held together by interchain hydrogen bonding, providing high tensile strength.

$\Psi_w$ (Water Potential)

A property of cells that remains unaffected by the presence of starch, glycogen, or cellulose because these macromolecules are insoluble in water.

Benedict's Test

A semi-quantitative test for reducing sugars where a solution is heated with Benedict's reagent, with a positive result indicated by a brick-red precipitate.

Test for Non-Reducing Sugars

A procedure involving boiling a solution with dilute hydrochloric acid, neutralizing it with sodium bicarbonate, and then performing Benedict's test.

Iodine Test

A test for the presence of starch where the addition of iodine solution results in a blue-black coloration.