Question

A sample of the amino acid tyrosine is barely soluble in water. Would a polypeptide containing only Tyr residues, poly(Tyr), be more or less soluble, assuming the total number of Tyr residues is the same in both cases? Explain.

Answer 1

Step-by-step explanation:

The first thing we need to know is that the amino acid of tyrosine has an aromatic ring within its structure.

Also, recall that aromatics hydrocarbons are considered to be unsaturated and non-polar.

So, since like dissolve like. Then, The non-polar character of tyrosine is enhanced by its aromatic ring. As a result, Tyrosine amino acid is much more soluble in less polar solvents like methanol and ethanol than in moderate highly polar water.

From the given information:

Since water is a very polar solvent, and tyrosine amino acid is not particularly polar, it is just barely soluble in it.

In addition to the aforementioned, peptides are strongly polar in nature. However, as the amount of tyrosine amino acids in a peptide increases, the region of the non-polar portion of the peptide increases (owing to the rise of the aromatic ring), and thus the non-polar value of the peptide will also rise. And this non-polar nature of peptide will make them more soluble in non-polar solvent and decrease its solubility in water (because water is polar in nature). And since peptides are non-polar, they would be more soluble in non-polar solvents and have less solubility in water.