The Different Roles of Macromolecules in Biology

The Different Roles of Macromolecules in Biology

There are four types of macromolecules that I am going to describe:

Proteins, carbohydrates, lipids and nucleic acid. I will also describe

the functions and why they are important in our bodies.

Proteins

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Proteins are polymers of amino acids that are joined head-to-tail in a

long chain that is then folded into a three-dimensional structure

unique to each type of protein. The covalent linkage between two

adjacent amino acids in a protein (or polypeptide) chain is called a

peptide bond.

There are twenty amino acids that make up proteins. Each amino acid

has a typical generic structure as depicted in the diagram 1, the only

variance in each amino acid lies in a unique side chain (R group).

Diagram 1: [IMAGE]

Most of the amino acids have a carboxyl group and an amino group as

shown above. At physiological pH the natural amino acids exist as

zwitterions, with a negatively charged carboxyl group and a positively

charged amino group. The side chains vary greatly in their complexity

and properties. Amino acids are classified by the chemical nature of

their side chains. Five of the 20 amino acids have side chains that

can form ions in solution and thereby can carry a charge. The others

are uncharged: some are polar and hydrophilic and some are non-polar

and hydrophobic.

Proteins are not linear molecules as suggested when we write out a

"string" of amino acid sequence, -Lys-Ala-Pro-Met-Gly- etc., for

example. Rather, this "string" folds into an intricate

three-dimensional structure that is unique to each protein. It is this

three-dimensional structure that allows proteins to function. Thus in

order to understand the details of protein function, one must

understand protein structure.

Protein structure is broken down into four levels. Primary structure

refers to the "linear" sequence of amino acids. Proteins are large

polypeptides of defined amino acid sequence (diagram 2). The sequence

of amino acids in each protein is determined by the gene that encodes