Question 11 Aspartic acid has a side chain bearing a carboxylic acid group; its pKa is 4. The a-amino and a-carboxylic groups have pKa values similar to those of alanine. Determine the net charge on an aspartic acid molecule at the following pH values: (for additional ungraded practice, see if you can identify which of the curves from the previous question correspond to Aspartic acid) pH = 1 +2 pH = 2.5 +1 pH = 4 0 pH = 9 -1 pH = 13 -2

22-91 Which amino acid does not rotate the plane of polarized light?

22-35 Why is histidine considered a basic amino acid when the pKa of its side chain is 6.0?

22-47 How many different tetrapeptides can be made (a) if the peptides contain the residues of asparagine, proline, serine, and metbionine and (b) if all 20 amino acids can be used?

22-59 What is the effect of salt bridges on the tertiary structure of proteins?

22-89 What kind of noncovalent interaction occurs between the following amino acids? (a) Valine and isoleucine (b) Glutamic acid and lysine (c) Tyrosine and threonine (d) Alanine and alanine

A 1.00-mg sample of a pure protein yielded on hydrolysis 0.0165 mg of leucine and 0.0248 mg of isoleucine. What is the minimum possible molar mass of the protein? (MMleucine=MMisoleucine=131g/mol)

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

All amino acids have two ionizable functional groups: an α‑amino group (average p?a of 9.4) and an α‑carboxylic acid group (average p?a of 2.2). Aspartic acid has an ionizable side chain (R group) with a p?a of about 3.8. One of the possible ionization states of aspartic acid is shown in the image. The protonated form of the R group of aspartic acid is shown in the structure. The ratio of the protonated form to the charged (deprotonated) form depends on the p?a of the R group and the pH of the solution. Select all the pH values at which the charged form of the R group would predominate.

Complete the table for the ionizable groups of the fictitious amino acid hypothetinine. pka (to TWO decimals) Average charge of group when pH=pK (to ONE decimal) Group Ka alpha-carboxyl 1.38 x 103 alpha-amino 6.02 x 10-10