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Components of Cells
The Macromolecules
Glucose: formula

What is it?

Perhaps the most common and abundant carbohydrate is glucose, which is manufatured, stored and then used by all plants. It is also consumed, stored and used by many animals as a source of carbon and energy.

Glucose is a monosaccharide ("single sugar") that contains carbon, hydrogen and oxygen in amounts that conform to the general carbohydrate formula CnH2nOn, but this does not tell us much about its chemical, physical and structural properties. These were worked out by subjecting glucose to a number of chemical reagents, observing what happened, and then deducing something about the original glucose molecule from the changes that were seen taking place.

How many carbons?

If glucose is treated with hot hydriodic acid (HI) oxygen is removed from the molecule along with any functional groups that contain oxygen.

What happened: a small amount of the molecule hexane (a hydrocarbon) was produced.

What was deduced: the glucose molecule consists of six carbons are in a straight, unbranched chain.

What functional groups are at the ends?

(1) - If glucose is treated with hydrogen cyanide (HCN) a cyanohydrin is formed at one end. Similarly, if glucose is treated with a mild oxidizing agent (such as bromine in water) a mono-caboxylic acid (called glucuronic acid) is produced (-COOH).

What happened: it appears that one end of the glucose molecule has a functional group that can be oxidized to an acid group.

(2) - If the glucose molecule is treated with a much stronger oxidizing agent, such as dilute nitric acid (HNO3) both the functional groups at either end of the molecule react.

What happened: a di-acid (two-acid) molecule is produced called glucaric acid.

What was deduced: that at one end of the glucose molecule there is an aldehyde group that can be oxidized to the acid (-CHO --> -COOH) by these treatments; that the other end of the molecule is an alcohol group (-CH2OH); that there are six carbons in the glucose molecule (supporting the evidence above).

What is in the middle?

If glucose is treated in ways that convert any alcohol reactive group(s) into acetate group(s), ((CH3CO), the glucose molecule reacts vigerously.

What happened: either a penta-acetate ("5-acetate") or hexa-acetate ("6-acetate") molecule is produced.

What was deduced: that at least five of the carbon atoms in the glucose molecule have an alcohol functional group attached to them.

Basic chemical structure

Thus, the basic chemical formula for the glucose molecule is:

With the basic properties that it is

a hexose: (it has 6 carbons)

an aldose: (it has a -CHO aldehyde group at one end)

a monosaccharide: (it is a "single sugar")

© 2004, Professor John Blamire