ch 17 Carbohydrates: Functions, Structures, and Reactions

Monosaccharide

Simple carbohydrate most commonly consisting of three to six carbon atoms

Disaccharide

Carbohydrate formed by the combination of two monosaccharide units

Polysaccharide

Carbohydrate formed by the combination of many monosaccharide units

Isomers

Molecules that have the same chemical formula but differ in either how the atoms are connected or how the connected atoms are arranged in space

Structural Isomers

Isomers that differ only in their connectivity

Stereoisomers

Isomers that differ in the spatial arrangement of their atoms

Optical isomers

Compounds that have the ability to rotate the plane of plane-polarized light

Oxidation Reaction of Monosaccharides

Chemical reactions involving the loss of electrons from monosaccharides

Glycoside Formation

The process of forming glycosides from monosaccharides

Hydrolysis of Disaccharides

Chemical reaction that breaks down disaccharides into monosaccharides

Enantiomers

Stereoisomers that are non-superimposable mirror images

Maximum number of stereoisomers

2n, where n is the number of chiral carbon atoms

Fischer Projections

Depict three-dimensional shapes for chiral molecules, with the chiral carbon represented by the intersection of two lines

D-isomers of monosaccharides

Humans can only metabolize the D-isomers

L-isomers of amino acids

Most animals are able to utilize only the L-isomers to synthesize proteins

(+) enantiomer

Rotates light clockwise +2.6°

(-) enantiomer

Rotates light counterclockwise -2.6°

Classification of Monosaccharides

Questions to ask when classifying a monosaccharide include whether it is an aldehyde (aldose) or a ketone (ketose) and how many carbon atoms are present.

D series

Almost all natural monosaccharides belong to this series.

Cyclic hemiacetals and hemiketals

Formed by monosaccharides with at least five carbon atoms.

Haworth structure

Method of depicting three-dimensional carbohydrate structures.

Anomeric carbon

Former carbonyl carbon atom that is now chiral.

α anomer

Anomer with —OH on the anomeric carbon pointing down.

β anomer

Anomer with —OH on the anomeric carbon pointing up.

Anomers

Stereoisomers that differ in the 3-D arrangement of groups at the anomeric carbon.

Glycoside

General name for a carbohydrate containing an acetal or ketal group.

Glycosidic linkage

New carbon-oxygen-carbon linkage that joins the components of the glycoside to the ring.

Galactose

Hexose component of lactose and similar to glucose.

Fructose

Most important ketohexose, sweetest monosaccharide.

Maltose

Disaccharide containing two glucose units joined by α(1→4) glycosidic linkage.

Lactose

Disaccharide composed of galactose and glucose units joined by β(1→4) glycosidic linkage.

Sucrose

Disaccharide composed of fructose and glucose units joined by α1→β2 glycosidic linkage.

Polysaccharides

Condensation polymers containing thousands of units.