Proteins are composed of long chains of amino acids linked together through amide bonds. In the body, protease enzymes break down proteins into the individual amino acids by hydrolyzing the amide bonds. Propose a plausible curved arrow mechanism for the hydrolysis of the dipeptide shown below into the amino acids glycine and alanine under acidic conditions. H,0 HO. H* H2N он dipeptide glycine alanine

On complete hydrolysis, a polypeptide gives two alanine, one leucine, one methionine, one phenylalanine, and one valine residue. Partial hydrolysis gives the following fragments: Ala-Phe, Leu-Met, Val-Ala, Phe-Leu. It is known that the first amino acid in the sequence is valine and the last one is methionine. What is the complete sequence of amino acids?

Using both three- and one-letter codes for amino acids, write the structures of all possible peptides containing the following amino acids: (a) Val, Ser, Leu (b) Ser, Leu2, Pro

22-9 What is the difference in structure between tyrosine and phenylalanine?

22-97 Gelatin is derived from collagen by denaturation. Is a gelatin dessert likely to be a good source of dietary protein?

22-61 Polyglutamic acid (a polypeptide chain made only of glutamic acid residues) has an a-helix conformation below pH 6.0 and a random-coil conformation above pH 6.0. What is the reason for this conformational change?

All amino acids have two ionizable functional groups: an a-amino group (average pK, of 9.4) and an a-carboxylic acid group (average pK, of 2.2). Tyrosine also has an ionizable side chain (R group) with a pK, of about 10.1. One of the possible ionization states of tyrosine is shown. H3N-CH -C-OH CH2 ÓH At what pH would the structure be the predominant ionization state? Consider the ionization state of all three of the functional groups. The protonated form of the R group of tyrosine is shown in the structure. The ratio of the protonated form to the charged (deprotonated) form depends on the pK, of the R group and the pH of the solution. Select the pH value at which the charged form of the R group would predominate.

(a) Which of the common amino acids have more than one carboxyl group?

The first step in the catabolism of most amino acids is the removal of the nitrogen atom by transfer to an a-keto acid, a reaction catalyzed by an enzyme called a transaminase. The a-keto acid acceptor is often a-ketoglutarate. Modify the structures in the product to show the products of the transamination of cysteine. Be sure to show functional groups with the charge and number of attached hydrogen atoms appropriate for pH 7.4. transaminase + O=C H₂N-CH + CH₂ CH₂ CH₂ SH Incorrect H₂N || CH | CH₂ | CH₂ I || O || n | CH₂ T SH

Give the full name of the amino acid and based on the structure of the side chain is it hydrophobic or hydrophilic?