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ORGANIC CHEMISTRY-STUDY GDE./SOL.MAN.
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- 22-21 Explain why an amino acid cannot exist in an un-ionized form at any pH.arrow_forward22-20 Show how alanine, in solution at its isoelectric point, acts as a buffer (write equations to show why the pH does not change much if we add an acid or a base).arrow_forward22-45 Proteins are least soluble at their isoelectric points. What would happen to a protein precipitated at its isoelectric point if a few drops of dilute HCl were added?arrow_forward
- (a) Draw the Lewis structure for the amino acid phenylalanine, showing the amino group and the carboxylic group in their un-ionized forms. (b) Draw the Lewis structure for the zwitterionic form of phenylalanine. (c) Which of these structures will be the predominant form at physiological pH?arrow_forward22-92 Write the expected products of the acid hydrolysis of the following tetrapeptide:arrow_forward22-44 How can a protein act as a buffer?arrow_forward
- 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 alaninearrow_forwardWrite the Zwitter ionic form of aminoacetic acid.arrow_forwardAll 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.arrow_forward
- 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 10-10arrow_forwardAll amino acids share a common structure, a central (alpha) carbon with four groups attached. Which of these is NOT one of the four groups attached to the alpha- carbon? O an R group an ammonium group (-NH3+) O a carboxylate group (-COO) a hydronium grouparrow_forwardSee Appendix on p5 for list of amino acids. Aspartame is a sweetener. The structure of aspartame, along with the titration curve showing its pKal and pka2 is given below. 14 € 12 10 8 6 4 2 0 pK₂2 = 7.87 PK₁₁ = 3.19 0 0.5 1 Equivalents of NaOH a) Copy the structure of aspartame. i) 1.5 2 OH S NH₂ Aspartame LOCH 3 Identify the two ionisable groups. Re-draw the groups in their protonated forms, and label each with their pka. ii) Circle and identify the two amino acids in aspartame.arrow_forward
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