2. Selective synthesis of the tetrapeptide Ala-Val-Gly-Leu a. Work backward from Structure K to fill in the boxes in the multistep synthesis scheme below. Assume the desired product is purified after each reaction step. Boxes A, B, E, and H should each have a single amino acid with a protecting group. b. Provide names for each indicated structure, using 3-letter codes. The names do not have to take protonation state into account but should account for protecting groups. B R A F ; name: G Boc- a Boc-amino acid name: K H₂N. HOL OF₂ CF3 НО name: Start here and work backward -OEt an amino acid ethyl ester Ala-Val-Gly-Leu E ¡H R N=C=N N=C=N (EtOH) R R PN=C=N R NaOH (excess) R C name: D ! name: name: J name: | HOCF₂ НО 요 HO CF3 c. Suppose that you wanted to synthesize Ala-Lys-Glu using this same multistep synthesis method. What problem would occur? Propose a conceptual idea (not specific reactions) of how the problem could be solved. (Hint: look up the functional groups present in these amino acid structures)

о 6. What is the catalytic triad and what particular protein family would you find this? What is the general role of the catalytic triad? Predict what would happen if Asp were mutated to Gly. ructure formation of alpha heli

1The sugar alcohol often used in “sugarless” gums and candies is L-sorbitol. Much of this alcohol is prepared by reduction of D-glucose. Compare these two structures and explain how this can be.

5. Shown below are the first steps in the mechanism of a cysteine protease, which catalyses amide bond hydrolysis in a similar manner as serine proteases. (a) Complete this mechanisms, and (b) sketch the approximate reaction coordinate diagram for this catalyzed reaction relative to the uncatalyzed proteolysis. HN N HN cysteine protease

3. Respiration is related to how cells balance redox reactions in the metabolic pathway. It can be aerobic if there is plenty of oxygen present or anaerobic if not. In class, we discussed the respiratory quotient for triolein as a carbon source. A. Calculate the respiratory quotient (RQ) for aerobic oxidation of the triglyceride formed by glycerin and three stearic acids (tristearin). Draw the structure and write the stoichiometrically balanced equation for the complete breakdown of the triglyceride by oxidation to CO₂ and water. B. As in part A, draw the structure of sucrose, write the stoichiometrically balanced equation and determine the RQ for it's metabolic breakdown to CO₂ and water. C. Anaerobic respiration occurs when cells operate without dissolved oxygen. List at least 4 different chemicals that act as electron acceptors when oxygen is not present.

5. Suppose an enzyme needed a cysteine thiol (sulfhydryl) group for its catalytic activity, and catalysis required the Cys thiol to act as a nucleophile at the beginning of the catalytic cycle. That would mean the Cys residue had to be in its UNPROTONATED (conjugate base) form. If that particular Cys residue in that protein had a pKą of 7.5, what fraction (percent, or proportion) of the total enzyme molecules would have the Cys R group in its ACTIVE form at pH 7.0?

Modify isoleucine to show the predominant forms at pH 1, 7, and 13. Isoleucine has p?ap�a values of 2.4 (carboxyl group) and 9.7 (amino group).

1,2-dioleoyl-3-myristyl-sn-glycerolsn-16:0-12:0-16:0LLnO Consider the TAGS abovea. Which is most prone to lipid oxidation? Explain.b. Which has the highest melting point? Explain.c. Which will most likely convert fastest to the most stable polymorphic form. Explain.

a. Suppose that you have the peptide Ala-Gly-Tyr-His-Leu and you treat it with FDNB and then 6M HCl. Draw the structures of all the products that you will have in solution (assume all reactions to go to completion).

5. Consider the decarboxylation of dimethyloxaloacetate 7 to 3-methyl-2-oxobutyrate 8 shown below H3CO cat. Cu²+ & CO2 CH3OH (aq) cat. Cu²+ no reaction CH3OH (aq) 9 a. Provide a mechanism to account for the fact that Cu2+ catalyzes this reaction. b. In one sentence explain why Cu2+ does not similarly catalyze the decarboxylation of 9.