Amino acids group 3- carboxyl groups

Proteins are linear polymers of L-a-amino acids. The carboxyl group of one amino acid is linked to the amino group of another amino acid. The amide bond formed in the reaction is called a peptide bond (Figure 19.4). 

Which amino acids have carboxyl groups in their side chains (Group 3)... 

Which amino acids have carboxyl groups in their side chains (Group 3) Two amino acids, glutamic acid and aspartic acid, have carboxyl groups in their side chains. 

The polypeptides yield the same derivatives as the amino acids the carboxyl group can be converted into the acid chloride and a halogen acyl group can be attached to the amino group. Further, the benzoyl, the carbethoxyl and the naphthalene-sulpho compounds can be easily obtained the derivatives with the last mentioned are soluble with difficulty and may be made use of for characterising the polypeptides. The combination with phenylisocyanate also takes place readily, but these compounds are not so important as those of the amino acids for purposes of characterisation. 

The name of peptides is formed using the ending yl for those amino acids whose carboxyl group participates in the peptide bond ... 

Physical Properties. Glycine is a colourless crystalline solid soluble in water. Owing to the almost equal opposing effects of the amino and the carboxylic groups. its aqueous solution is almost neutral (actually, slightly acidic to phenolphthalein) and glycine is therefore known as a neutral ampholyte. f It exhibits both acidic and basic properties. 

This procedure is restricted mainly to aminodicarboxyhc acids or diaminocarboxyhc acids. In the case of neutral amino acids, the amino group or carboxyl group must be protected, eg, by A/-acylation, esterification, or amidation. This protection of the racemic amino acid and deprotection of the separated enantiomers add stages to the overall process. Furthermore, this procedure requires a stoichiometric quantity of the resolving agent, which is then difficult to recover efficiendy. Practical examples of resolution by this method have been pubUshed (50,51). 

In addition to the a-amino and a-carboxyl groups those amino acids with an extra ionizable group will also have a pvalue. Glutamic acid is an example of an amino acid with an extra acidic group (COOH) on the y-carbon, and lysine is an example of an amino acid with an extra amino group on the e-carbon atom. As a result they each have three ionizable groups and three pKa... 

Amino acid Extra ionizable group a-Carboxyl P a. a-Amino P a2 Extra group PA ... 

One of useful building blocks for the synthesis of 2-(l//)-pyrazinones is iV-BOC amino acids, whose carboxylic acid moiety reacts with the amino group of another component having cyano or carbonyl functionality at the a-position, such as a-amino nitriles <2004T835>, a-amino amide (Scheme 46) <2000H(53)1559>, a-amino ketones... 

Attachment of carboxyl-terminal amino acid to reactive group on resin. 

Creating acidic groups (carboxylic acids and phenol groups) on the internal soot surface by chemical oxidation with, e.g., chromic acid, fixation of cationic complexes of the catalyst (e.g., amino complexes of Pt(II) or Pt(IV) at the inner surface of the soot particles by ion exchange, followed by chemical or electrochemical reduction of these complexes... 

Correct answer = A. The peptide bond has a partial double-bond character. Unlike its components—the a-amino and a-carboxyl groups—the components of the peptide bond do not accept or give off protons. The peptide bond is not cleaved by organic solvents or urea, but is labile to strong acids. It is usually in the trans configuration. 

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