140C FINAL old KEY

140C FINAL old KEY - Chemistry 140C (Finn) Spring 2008 –...

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Unformatted text preview: Chemistry 140C (Finn) Spring 2008 – Final Exam Problems that Didn’t Make it Onto the Test Answer Key 1. (with apologies to the vegetarians in the class) The process that produces the dark color and much of the flavor when meat is browned is called the Maillard reaction. (Interesting factoid: there exists an organization called “The International Maillard Reaction Society.” Really.) As you might imagine, the Maillard reaction occurs between sugars and proteins, two common components of food, usually under mildly acidic conditions. There are three main steps. The first two are shown here. Step 1 O OH HO HO OH OH R H 2 N + H N O OH HO HO OH R heat sugar protein pH 2-7 Step 2 NHR O HO OH OH OH H N O OH HO HO OH R heat pH 2-7 (a) What part(s) of a polypeptide could provide the amine reactant in step 1? (You can look up the amino acids in your book; if this was on the test, I would give you a list.) The amine-containing side chain of lysine, also the guanidine side chain of arginine. And don ’ t forget the free amine at the N-terminus of the polypeptide! (b) Show arrow-pushing mechanisms for the first two steps in the process: Step 1: O OH HO HO OH OH R H 2 N + H N O OH HO HO OH R heat sugar protein pH 2-7 O OH HO HO OH OH 2 O OH HO HO OH R H 2 N H 2 N O OH HO HO OH R RNH 2 as base RNH 3 Page 2 of 10 Step 2: NHR O HO OH OH OH H N O OH HO HO OH R heat pH 2-7 N O HO HO HO OH R H H N OH HO HO HO OH R H NHR OH HO OH OH OH H H 2 O NHR OH HO OH OH OH tautomerization (I don't need to draw this out, do I?) (c) Many different things can happen in the third step of the Maillard reaction. One such reaction is shown here: a dehydration reaction upon heating. Draw a mechanism for this reaction, too.reaction, too....
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This note was uploaded on 09/08/2008 for the course CHEM 140C taught by Professor Nefzi during the Spring '06 term at UCSD.

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140C FINAL old KEY - Chemistry 140C (Finn) Spring 2008 –...

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