What Are Carbohydrates
And
What Function Do They Serve ?
Carbohydrates, or saccharides as they are also known ,represent a large class of biological molecules, which serve a variety of roles in living organisms. The name carbohydrates was given to this class of molecules when chemists only knew the simple stoichiometry of saccharides. During this time they were simply considered to be hydrated carbons . Most carbohydrates contain this monomer (CH20)n or can be derived from substances that do. Carbohydrates or saccharides may be split into three categories: monosaccharides, disaccharides, and polysaccharides.
Monosaccharides, the simplest monomeric sugars, are the building blocks for all of the other saccharide classifications. It is the linking which occurs between these monomers which leads to the more complex structures of oligosaccharides, disaccharides, and polysaccharides.
The smallest molecules which are considered to be monosaccharides are a part of the triose class and usually contain three carbon atoms (n=3). The two subdivisions of trioses are the aldoses and ketoses. There are only two trioses glyceraldehyde and dihydroxyacetone. Glyceraldehyde is a aldehyde which makes it an aldose and dihydroxyacetone is a ketone which makes it an ketose. These two molecules are tautomers ( structural isomeres differing in the location of their hydrogens and double bonds.) They may interconvert via an enediol intermediate.
Function of Monosaccharides:
3) Biological structural components.
Oligosaccharides
Oligosaccharides are saccharide molecules which are composed of only a few monomer units. The simplest form of oligosaccharides involves the disaccharides, which involve only two residues. Saccharides such as sucrose, lactose, and trehalose,serve as soluble energy stores in plants and animals. Disaccharides such as maltose and cellobiose can be regarded primarily as intermediate products in the degradation of longer polysaccharides.
Polysaccharides
Polysaccharides are long polymers of monosaccharides. Polysaccharides may be composed of many types of sugar monomers. Polysaccharides serve a variety of functions including the storing of sugar molecules in plants and in animals. Others, like cellulose, chitin, are involved in the cell walls of bacteria and serve to provide structural support.
Polysaccharides are analogous to proteins in that they also have distinguishable types of structures (primary, secondary structures.) If a polysaccharide is composed of only one kind of monomer residue (B-D-glucose for cellulose); it is referred to as a homopolysaccharide. If they are composed of two or more they are referred to as heteropolysaccharides. However even the most complex of polysaccharide structures are relatively simple when comparing them to that of proteins. For the most part no more than two different types of residues are usually involved. Polysaccharides are different than proteins in that they have random lengths. The function of polysaccharides is directly related to their structure. Depending on the specific role of a polysaccharide, it may or may not require a complicated three dimensional shape which is most often involved when observing the structure of proteins. For example, polysaccharides such as starch are simply long chains because their function only requires that they store energy. On the other hand, molecules such as the oligosaccharides which may be found on the surface of certain glycoproteins, serve the role of identifying cells or molecules with complex three dimensional structures because they must interact with other molecules and convey information.
Project-Related Links
Project Five Main Page
Overview of Carbohydrates Page
Photosynthesis
Metabolism
Food for Thought...