Carbohydrate Chemistry Overview

Study Notes

Carbohydrates are aldehyde or ketone derivatives of polyhydric alcohols, meaning they have more than one hydroxyl group.
They are polyhydroxy-aldehydes or polyhydroxy-ketones.
The general formula is (CnH₂nOn).

Carbohydrates are the primary source of energy for animals and humans.
They store energy in the form of starch (plants) and glycogen (animals).
They supply carbon for the synthesis of other compounds such as proteins.
Carbohydrates form important structural components in animal and plant cells, including cell membranes.
They are crucial parts of nucleic acids, free nucleotides, coenzymes, hormones, and their receptors, and enzymes.

Monosaccharides: Simple sugars, the simplest form of sugars, cannot be further hydrolyzed.
Disaccharides: Composed of two monosaccharide units, such as sucrose.
Oligosaccharides: Contain 3 to 10 monosaccharide units, forming monosaccharides via acid hydrolysis.
Polysaccharides: Contain more than 10 monosaccharide units, forming monosaccharides via acid hydrolysis.

Definition: Building blocks of carbohydrates; the simplest sugars that cannot be hydrolyzed.
Classification:
- Aldoses: Contain aldehyde groups, like glyceraldehyde.
- Ketoses: Contain ketone groups, like dihydroxyacetone. Ketoses are indicated with the suffix -ulose.
Based on the number of carbon atoms: Trioses (3), Tetroses (4), Pentoses (5), Hexoses (6), Heptoses (7). Examples of these include glyceraldehyde, ribose, glucose, fructose, etc.

An asymmetric carbon atom is attached to four different groups or atoms.
This makes a molecule optically active, meaning it can rotate plane-polarized light.
Dextrorotatory (d or +): Rotates light to the right.
Levorotatory (l or -): Rotates light to the left.

Haworth's projection formula shows that monosaccharides predominantly exist in cyclic forms (ring structures).
Open-chain forms are less common (less than 1%).
Pyranose: Six-membered ring, with five carbons and one oxygen.
Furanose: Five-membered ring, with four carbons and one oxygen.

Isomers are molecules with the same chemical formula, but different arrangements of atoms.
- Functional group isomerism: Same carbon skeleton but different functional groups (aldehyde vs. ketone).
- Enantiomers (D/L isomerism): Non-superimposable mirror images (differ in spatial arrangement of H/OH groups around an asymmetric carbon).
- Anomers (α/β isomerism): Differ only in the positioning of a hydroxyl group around the anomeric carbon atom, formed during ring closure.
- Epimers: Differ in the arrangement of H/OH groups on one, non-anomeric carbon atom. Examples including glucose, mannose, and galactose.