Molecular structure of glucose and other carbohydrates
To the right of this page I have put a number of links to other files on this website showing 3-D molecules of carbohydrates, which offer the opportunity to see and interact with these molecular models in 3 dimensions.
At the bottom of the page there are also links to related topics at this level on the BioTopics website
Glucose is an example of a carbohydrate which is commonly encountered. It is also known as blood sugar, and dextrose.
Its chemical formula is C6H12O6, and this empirical formula is shared by other sugars - called hexoses - 6 carbon sugars. You may wish to know in some detail how these 24 atoms are arranged in the molecule of glucose - the structural formula.
In some books you may see diagrams of the glucose molecule looking like this: This so-called stick diagram really only describes how things are in dry (powder) glucose.
In life - in your blood and inside cells of plants and animals - most of the glucose consists of molecules shaped into a ring (actually a 6-sided figure, a hexagon) which may be drawn with this fairly simple format:
Note that there is an oxygen atom forming part of the ring, and that there are simple lines drawn making up the rest of the ring, and a section sticking out to one side. These lines represent carbon atoms, and -H and -OH groups, most of which have been left out for simplicity. Sometimes the details of just some of these -H and -OH gr oups are drawn in at one end (or both ends). This is because the orientation of these groups slightly alters the chemistry of the molecule, so the resulting molecules are given different names.
alpha glucose beta glucose
In alpha glucose the -H group of the rightmost Carbon atom (C1) is above the plane of the ring, whereas it projects below the ring in beta glucose.
There are in fact 3 versions of the ring structure called chairs and boat, depending on the bending in or out of the left and right corners, but it is easier to draw it as a flat hexagon.
Some of the lines may be thickened or flared out to give an impression of 3D structure on the page
All the other groups can vary in different hexose sugars, which result in slightly different chemical properties.
It is worth knowing the numbers used to describe each of the 6 carbon atoms.
This numbering is important when glucose units are joined together.
1-4 linkages (formed by glycosidic bonding) result in a simple linear (end to end) connection, which is found in maltose, a disaccharide:
Repeating the condensation process will result in the polysaccharide starch, which is considered to have 2 components, amylose and amylopectin.
The chain of 1-4 linkages so formed can be quite long, and may wind up into a helix. This is the situation in amylose, (a linear part of which is shown here):
On the other hand, 1-6 linkage causes the formation of a branching point which then allows another chain of 1-4 linkages to develop. This 3-D branching also produces other points at which glucose may be added by condensation or removed by hydrolysis. This branching occurs in amylopectin, (a small section of which is shown here):
This basically explains the structure of starch and glycogen.
This topic has connections with other BioTopics units :-
Monomers and polymers,
Some computer programs can display molecular structure in a variety of formats, some of which are commercially protected. A variety of open source programs have been released to enable more general educational use, mostly originating in a program called Rasmol.
On this site I have tried several different ways of displaying molecules in 3 dimensions.
There are 3 sub-menus, using different ways to show biological molecules:
Conversion nearly complete: carbohydrates, lipids, amino acids, proteins, nucleic acids, vitamins, antibiotics at present - still capable of expansion ...
Jmol - using Java applets - likely to be blocked by some computers - but quite a lot of different types of biological molecules on display
Chime - using a prehistoric browser plugin - just a few molecules , only visible if you have the correct plug-in.