Question

Describe the chemical properties of amino acids and discuss how they can affect the final structure of a folded protein. In your answer, give examples of amino acid substitutions that could cause changes to a protein’s structure and function

Answer 1

Chemical reactions of amino acids due to carboxyl and amino groups:

I) Due to Carboxyl group:

a) Decarboxylation:

The amino acids will undergo alpha decarboxylation to form the corresponding “amines”. Thus important amines are produced from amino acids.

• Histidine   → Histamine + CO2
• Tyrosine    →Tyramine + CO2
• Tryptophan   →Tryptamine + CO2
• Lysine     →Cadaverine + CO2
• Glutamic acid    → Gamma Amino Butyric Acid (GABA) + CO2

b) Reaction with Alkalies (Salt formation):

The carboxyl group of amino acids can release a H+ ion with the formation of Carboxylate (COO–) ions. These may be neutralized by cations like Na+ and Ca+2 to form Salts. Thus amino acids react with alkalies to form “Salts”.

c) Reaction with Alcohols (Esterification) :

When the amino acids is reacted with alcohol to form, “Ester”. The esters are volatile in contrast to the form amino acids.

These are the some chemical properties of amino acids.

Amino acid affects the protein structure:

The gene, or sequence of DNA, ultimately determines the unique sequence of amino acids in each peptide chain. A change in nucleotide sequence of the gene's coding region may lead to a different amino acid being added to the growing polypeptide chain, causing a change in protein structure and therefore function.

Example :

All amino acid substitutions for the catalytically active histidine in the enzyme chloramphenicol acetyltransferase result in an almost complete loss of enzyme activity.