Carboxylic acids

Hi,

I don't think the statement that "carboxylc acids cannot exist as more than dimers" is at all true; so your confusion is unnecessary.

The best example is that of amino acids, which can form very long (often tens of thousands of a.a.'s long) "polymers", namely proteins. Athough most proteins will have many different amino acids (even some with more than one carboxyl group (-COOH) e.g. aspartic acid, there are several examples of tripeptides and other oligopeptides which only contain one amino acid e.g. collagen is rich in hydroxyproline;keratin has part-chains of cysteine (a sulphur-containing a.a.)

I hope this puts your mind at rest.

M

Hi,

I don't think the statement that "carboxylc acids cannot exist as more than dimers" is at all true; so your confusion is unnecessary.

The best example is that of amino acids, which can form very long (often tens of thousands of a.a.'s long) "polymers", namely proteins. Athough most proteins will have many different amino acids (even some with more than one carboxyl group (-COOH) e.g. aspartic acid, there are several examples of tripeptides and other oligopeptides which only contain one amino acid e.g. collagen is rich in hydroxyproline;keratin has part-chains of cysteine (a sulphur-containing a.a.)

I hope this puts your mind at rest.

M

Why can’t carboxylic acids exist as more then dimers? There will be still one negatively polar oxygen when dimers form

Amino acids don't exist as carboxylic acids if they've reacted to become a protein... If anything, they are amides?

Biological amino acids have an amine group and a carboxylic acid group, which are what they use to polymerise, AND a residual group or R group, which varies between the ~20 amino acids. Aspartate and glutamate are the two amino acids that have carboxylic acid groups in their R groups.

Chemically speaking, yeah, amino acids form amide bonds when they polymerise. Biochemists tend to call those peptide bonds, although I’m not entirely sure why.