1. (38 pts.) 2. (25 pts.) 3. (15 pts.) 4. (12 pts.) 5. (10 pts.) Bonus (12 pts.) TOTAL (100 points)

Transcription

1 Moorpark College Chemistry 11 Spring 2010 Instructor: Professor Torres Examination #5: Section Five May 4, 2010 ame: (print) ame: (sign) Directions: Make sure your examination contains TWELVE total pages (including this cover sheet) when instructed to do so. Answer all the questions in the spaces provided. Be sure to show all your work for partial credit. The last two pages of this examination consist of the necessary amino acids and periodic table. Question 1. (38 pts.) 2. (25 pts.) 3. (15 pts.) 4. (12 pts.) 5. (10 pts.) Bonus (12 pts.) TTAL (100 points) Points

2 Chemistry 11 Spring 2010 Examination #5 1. (38 pts. total) The first portion of this examination will focus on obiloside (shown below), a molecule shown to inhibit neuraminidase from the bacterium Clostridium perfringers: C C obiloside C A. (6 pts.) Which of the terms below correctly describe the structural features present in obiloside? Circle each appropriate description. Furanose Carboxylic Acid Glycosidic bond Pyranose emiacetal Steroid Aldose Acetal onreducing sugar Ketose Peptide bond Reducing sugar B. (8 pts.) For each of the circled terms in Part A, label ALL the specific structural features on the molecule shown above. For example, if a glycosidic bond is present, the exact type should be fully described and properly labeled EAC time for credit. C. (2 pts.) Is obiloside expected to give a positive test with Fehling s reagent? Briefly explain why or why not. D. (3 pts.) Consider the hydrolysis of obiloside with a strong acid such as Cl. Will the resulting products give a positive test with Benedict s reagent? Briefly explain why or why not.

3 E. (3 pts.) A student performs the Lieberman-Burchard reaction (which uses chloroform, acetic anhydride, and sulfuric acid as reagents) on a sample of obiloside. The reagents are added to the molecule, and the student waits 5 minutes. What results should s/he expect? Briefly explain your conclusion. The following questions for Parts F G involve ring A as labeled below: C C ring A obiloside C F. (6 pts.) Convert ring A to its open-chain (Fischer projection) form.

4 C C ring A obiloside C G. (4 pts.) Your answer to Part F should reflect formation of the Fischer projection for D-Glucuronic acid, a compound commonly converted in the liver to glucuronides and excreted in the urine. D-Glucuronic acid can be formed by the enzyme-catalyzed oxidation of a well-known starting material at carbon-6. Draw the Fischer projection (in the box below) for this starting material and identify the monosaccharide that you drew. Enzyme-catalyzed oxidation Part F Answer ame of monosaccharide?. (6 pts.) Finally, convert the appropriate components of obiloside into chair conformations if/where applicable.

5 2. (25 pts. total) MRE BICEMICAL STRUCTURES! Important note: use the space provided along with the back pages of this examination for any scratch work to draw the requested items below. All final structures should be drawn in the boxes provided below to receive any credit. A. (5 pts.) aworth projection for the α form of a disaccharide in which two units of D-fructofuranose are joined by a β-2,4-glycosidic bond. B. (4 pts.) parallel β-sheet containing FUR total valines. Make sure to denote any important hydrogen bonding as well as stereochemistry.

6 C. (8 pts.) the formation of a triglyceride from glycerol and the three fatty acids shown below (used one time each): leic acid: C 3 (C 2 ) 5 C=C(C 2 ) 7 C γ-linolenic acid: C 3 (C 2 ) 3 (C 2 C=C) 3 (C 2 ) 4 C Arachidonic acid: C 3 (C 2 ) 3 (C 2 C=C) 4 (C 2 ) 3 C D. (8 pts.) Tripeptide consisting of asparagine, proline, and arginine in which the C-terminus residue is asparagine, and the -terminus residue is arginine under natural conditions. Make certain to include appropriate stereochemistry. 1) Are there any peptide bonds present in your structure above? If so, label each one. 2) If the amino acids at the -terminus and C-terminus are switched, will the resulting molecule have the same physical properties as the original tripeptide in part D? Briefly explain why or why not.

7 3. (15 pts. total; 3 pts. each) Identify the predominant type of noncovalent interaction occurring between the following amino acids. Draw the structure of the amino acid pair with the interacting groups facing each other, and show the type of interaction clearly wherever possible. A. Serine and glutamic acid B. Arginine and aspartic acid C. Phenylalanine and tryptophan D. Cysteine and cysteine E. Tyrosine and tyrosine

8 4. (12 pts. total; 1 pt. per blank) FILL-I-TE-BLAK! A. ydrolysis of lactose yields and. B. The process of involves a triglyceride reacting with a strong base. C. contains 25% protein and 50% cholesterol. D. In the form, a single protein chain twists in such a manner that its shape resembles a right-handed coiled spring. E. The structure of a protein involves interactions between subunits in a protein that has more than one polypeptide chain. F. is a linear polysaccharide of D-glucose units joined by only β-1, 4-glycosidic bonds. G. is composed of continuous, more than two unbranched D-glucose units joined by only α-1, 4-glycosidic bonds.. changes the secondary, tertiary, and quaternary structures of a protein but does not affect its primary structure. I. is the change in specific rotation that accompanies the formation of an equilibrium mixture of α and β anomers in aqueous solution. J. D-fructose and L-fructose are of each other. K. In the lab, cholesterol gives a negative test because it does not contain glycerol. (Continued on next page)

9 5. (10 pts. total) The structure of a lecithin molecule is shown below. Answer the questions that follow: A. (1 pt.) What kind of a biomolecule is lecithin? B. (3 pts.) There are four main components of lecithin. ne of these is choline. What are the other three? C. (2 pts.) Does lecithin have a polar region? If so, circle the region. D. (4 pts.) Mayonnaise is a smooth and creamy substance made from vegetable oil (nonpolar) in lemon juice or vinegar (polar). As we already know, oil does not mix with water. Yet, the oil and lemon juice in mayonnaise seem to be well dispersed. This is due to egg yolk, another ingredient in mayonnaise. Egg yolk contains lecithin, which acts as an emulsifier (a type of surfactant typically used to keep mixtures of immiscible fluids well dispersed). Why is lecithin used as an emulsifier in mayonnaise?

10 BUS! (12 pts. total; 2 pts. per correct structure) Consider the structural formula of coenzyme A shown below, an important biomolecule: 2 S P P P Using your acquired lecture and laboratory knowledge involving organic reactions to date, draw the structural formulas for the expected products of complete hydrolysis of coenzyme A in aqueous Cl. int: the phosphorus double bond oxygen component behaves similar to an ester.

11 ydrophobic nonacidic side chains 3 C Glycine Gly, G 3 C 3 C Alanine Ala, A 3 C Valine Val, V 3 C Leucine Leu, L 3 C Isoleucine Ile, I 2 C Proline Pro, P 3 C Tryptophan Trp, W 3 C Phenylalanine Phe, F 3 CS 2 C 2 C 3 C Methionine Met, M ydrophobic acidic side chains 3 C ydrophilic nonacidic side chains 3 C 3 ydrophilic acidic side chains 2 C 3 Serine Ser, S C S Aspartic acid Asp, D C Threonine Thr, T 2 C Cysteine Cys, C 3 Se C C C Asparagine Asn, Glutamic acid Glu, Q Selenocysteine Sec, U Glutamine Gln, Q C C Tyrosine Tyr, Y 2 ydrophilic basic side chains 3 C 2 3 C 3 C Lysine Lys, K Arginine Arg, R istidine is,