Carbohydrates- Biologically Important Monosaccharides and Disaccharides

When presented with a structure, be able to recognise the structural modifications of monosaccharides.

Be able to recognise the functional groups in modified monosaccharides.

There are many different derivatives of monosaccharides.

One of these is the sugar alcohol, in which the aldehyde/ketone group has been reduced to form another -OH group. These are often used in artificial sweeteners.

A second derivative is the deoxy sugar, such as deoxyribose, found in DNA. Deoxyribose sugars are simply sugars with one or more -OH groups replaced with hydrogens.

A third derivative is the amino sugar, which is a sugar with -NH2 (instead of -OH) on the second carbon.

Sugar phosphates are sugars with phosphate groups esterified onto one of the Cs. Adenosine triphosphate and other nucleotides are prime examples.

Be able to explain a glycosidic bond.

Glycosidic bonds are bonds formed between sugars. They are formed between the -OH group of C1 of one sugar and the -OH group of any other C (I think) of the other sugar.

Be able to recognise the type of glycosidic bond(s) in a disaccharide or polysaccharide (alpha or beta).

As I just mentioned, one of the participating groups in the bond is always the -OH group of C1 of one sugar. C1 is also the anomeric carbon, which can be in alpha or beta form (see my first post on carbohydrates for more information). If C1 is in alpha form, the glycosidic bond is alpha; if C1 is in beta form, then the glycosidic bond is beta.

Know the composition and the function of starch.

Starch is a way in which plants store glucose. It is found in two forms: amylose and amylopectin. Amylose is a linear structure, consisting of glucose units all linked together with alpha(1->4) bonds (i.e. bonds from the C1 of the first carbon to the C4 of the next). The last carbon is not attached to anything and is therefore free to reduce other things. Amylopectin, in contrast to amylose, is highly branched. Some glucose units are linked together with alpha(1->4) bonds, but every 12-30 residues there is also a branch consisting of an alpha(1->6) bond.

Know the composition and function of cellulose.

Cellulose, like starch, consists of chains of glucose molecules. Instead of storing glucose for future use, however, cellulose plays major structural roles in plant cells. Cellulose, like amylose, is linear, but unlike amylose, it has beta(1->4) bonds. The different orientation of these bonds causes cellulose to form extended ribbons which can pack together efficiently, whereas amylose tends to form helices. The -OH groups of glucose allow the extended ribbons of cellulose to form interchain bonds, providing extra stability.

Know the difference between a homopolysaccharide and a heteropolysaccharide.

A homopolysaccharide is a polysaccharide (a carbohydrate consisting of many sugars joined together) with only one type of sugar. A heteropolysaccharide, on the other hand, has different kinds of sugars.

Know the difference between a monosaccharide and a polysaccharide.

Kinda interesting that this is the last dot point, but whatever. A monosaccharide is a simple sugar, while a polysaccharide is a long chain made up of these monosaccharides.