Structural Biochemistry/Carbohydrate Terms
Structural Biochemistry Carbohydrate Terms
- MONOSACCHARIDE: Monosaccharides are the simplest carbohydrates and are either ketoses or aldoses that have two or more hydroxyl groups. Monosaccharides typically have the empirical formula (C-H2O)n, which is a carbon hydrate, and are important fuel molecules as well as building blocks of nucleic acids.
- KETOSE: Ketoses are carbohydrates that contain a keto group or simply a ketone like dihydroxyacetone.
- ALDOSE: Aldoses are carbohydrates that contain an aldehyde group like glyceraldehyde.
- ENANTIOMER: Enantiomers are mirror images of one another. Every chiral center on a molecule must have the opposite configuration. Enantiomeric carbohydrates have either the D or L form.
- DIASTERIOMER: Diasteriomers are molecules that have opposite configurations at one or more of the chiral centers but at least one chiral center must remain the same. Therefore diasteriomers are not mirror images of one another.
- EPIMER: An epimer is a sugar that differs in configuration at a single asymmetric center. For example D-glucose and D-mannose are epimeric at C-2.
- HEMIACETAL: Hemiacetals form when an aldehyde reacts with an alcohol. Carbohydrates with an aldehyde group or aldoses in open-chain forms will cyclize into rings by forming a hemiacetal.
- HEMIKETAL: Hemiketals form when a ketone reacts with an alcohol. Carbohydrates with a keto group or ketoses in open-chain forms will cyclize into rings by forming a hemiketal.
- ANOMER: The C-1 carbon atom is called the anomeric carbon atom. The alpha and beta forms are called anomers. The alpha designation means that the hydroxyl group attached to C-1 is on the opposite side of the ring from the CH2OH at the carbon atom that determines whether the sugar is designated D or L. The beta designation means that the hydroxyl group is on the same side as the CH2OH at the chiral center.
- GLYCOSIDIC BOND: Glycosidic bonds can join one monosaccharide to another. These bonds are formed by the reaction of a hemiacetal or a hemiketal with an alcohol to form a acetal or a ketal respectively with the loss of water. So the formation of a glycosidic bond is a dehydration reaction.
- REDUCING SUGAR: A reducing sugar can act as a reducing agent and is any sugar the in solution has an aldehyde or a ketone group; like for example Maltose.
- NONREDUCING SUGAR: A nonreducing sugar cannot act as a reducing agent and is any sugar the in solution will not convert to an aldehyde or a ketone group; like for example Sucrose.
- GLYCOPROTEIN: A carbohydrate group can be covalently attached to a protein to form a glycoprotein. Glycoproteins are components of cell membranes. Carbohydrates are linked to proteins through Asparagine in an N-linkage or through Serine or Threonine in an O-linkage. Glycosylation sites can be detected within amino acid sequences.
- PYRANOSE: A pyranose is a carbohydrate that has a five-carbon and oxygen ring in its chemical structure.
- FURANOSE FORM: A pyranose is a carbohydrate that has a furan ring structure with four carbons and an oxygen atom.
- CONFORMATIONAL ISOMERS: Molecules that differ from each other only by rotation across a single bond.
- HOMOPOLYSACCHARIDE: A carbohydrate chain that consists of only one kind of carbohydrate monomer.
- HETEROPOLYSACCHARIDE: A carbohydrate made of more than one type of monomer.
- GLYCOSYLATION: This is the process by which carbohydrates are added to proteins or lipids, or other molecules as well.
- LECTINS: Promote interactions between cells.
- OLIGOSACCHARIDE: It is a carbohydrate chain that consists of three to ten residues.
Berg, Jeremy M., Tymoczko, John L., and Stryer, Lubert. Biochemistry. 6th ed. New York, N.Y.: W.H. Freeman and Company, 2007.