14.8 (b) Natural macromolecules

14.8 (b) Natural macromolecules

Food’s main constituents are proteins, fats and carbohydrates.

Proteins contain the same linkages (amide links) as nylon, but with different units. Similarly, lipids and terylene both have ester links but different units.

The structure of a protein is:

In digestion proteins are broken down into amino acids (hydrolysis).

Fats are esters possessing the same linkage as Terylene (ester links) but with different units.

Soap is a product of the hydrolysis of fat. It is done using sodium hydroxide (as opposed to acid, in digestion). The hydrolysis gives glycerol and the sodium salts of fatty acids. The salts are used as soaps.

Complex carbohydrates: are a large number of joined sugar units (monosaccharide like glucose). The sugar units are represented like this:

They join together in a condensation polymerisation:

In digestion, the hydrolysis (Decomposition of a chemical compound by reaction with water, such as the dissociation

of a dissolved salt or the catalytic conversion of starch to glucose, which can be accelerated by an acid or base) of starch happens in the mouth by the enzyme amylase to make glucose.

In the lab, unless you have enzymes, you have to boil the complex carbohydrate (or proteins or fats) in acid the products will be the following:

-starch → glucose

-proteins → amino acids

-fats → fatty acids and glycerol

But if hydrolysis is not complete, the macromolecules are not completely broken down. So you get a mixture of molecules of different sizes for example for starch you get, glucose, maltose (2 glucose units) and maltotriose (3 glucose units). Chromatography can be used to identify the products and the substances. However, amino acids and sugars are colourless when dissolved in water, so a locating agent is used. The substances can be identified using the Rf values or by matching them with spots which are horizontal.