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Lipids, Carbohydrates, Nucleobases & DNA

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Lipids, Carbohydrates, Nucleobases & DNA Chemistry 2050 “Introduction to Organic Chemistry” Fall Semester 2011 Dr. Rainer Glaser Examination #5: The Final - Practice Edition “Lipids, Carbohydrates, Nucleobases & DNA.” Wednesday, December 12, 2011, 10 am – 12 pm. Name: Answer Key Question 1. Lipids and Detergents. 20 Question 2. Glyceraldehyde and Carbohydrates. 20 Question 3. Nucleobases of DNA and RNA. 20 Question 4. Ribose and Deoxyribose and Their Phosphate Esters. 20 Question 5. Single and Double Strands of DNA. 20 Total 100 — 1 — Question 1. Lipids and Detergents. (20 points) (a) Draw the line segment drawing of glyceryl tristearate. This fat is the _TRI-ester formed between one molecule of the triol ___GLYCEROL____ and three molecules of the fatty acid stearic acid, H3C−(CH2)16−COOH. To convert this fat into soap, one would cook the fat with aqueous NaOH solution, a process that is called __SAPONIFICATION__. (10 points) (b) A simple micelle is shown schematically on the right. Each circle signifies a _________ (polar, nonpolar) head-group, and each wiggly line signifies a ________ (polar, nonpolar) alkyl chain. In the case of “normal” soap, the head- group is a ___CARBOXYLATE__ anion. Indicate where we would find the associated cations (i.e., sodium cations; draw a few in the scheme). Water is on the __________ (inside, outside) of this micelle and fats will accumulate on the _________ (inside, outside) of this micelle. (10 points) — 2 — Question 2. Glyceraldehyde and Carbohydrates. (20 points) (a) The structure shown is the ____ (R, S) enantiomer of glyceraldehyde. Mark the chiral carbon with a star. C in center Highest priority substituent: _OH__ Lowest priority substituent: __ H __ The “list” of the carbonyl-C: C(O O H ) The “list” of the alcohol-C: C(O H H) (10 points) (b) The Newman projection is shown of a D-tetrose. The structure is D-_____________ (erythrose, threose). Draw the corresponding Fischer projection on the right. (4 points) (c) Draw the Fischer projection of D-glucose. The molecular formula of glucose is C6H12O6. Glucose is an __________ (aldose, ketose). (6 points) — 3 — Question 3. Nucleobases of DNA and RNA. (20 points) (a) Nucleobases. Mark each box with “yes” or “no” and, for the last row, provide the single-letter abbreviation of the complementary base in the Watson-Crick base-pair. (16 points) Adenine Guanine Cytosine Thymine Uracil Occurs in DNA: Yes Yes Yes Yes NO Occurs in RNA: Yes Yes Yes NO Yes Is a Purine Derivative: Yes Yes NO NO NO Is a Pyrimidine Derivative: Yes Yes Yes Yes Yes Contains an Amino (NH2) Group: Yes Yes Yes NO NO Contains an Imidazole: Yes Yes NO NO NO Contains a Cyclic Amide: NO Yes Yes Yes Yes Base-Pairs with: T C G A A (b) Tautomers of Nucleobases. Guanine is a tautomer of 2-amino-6-hydroxy-9H-purine. Pick the tautomer that occurs in DNA. (4 points) — 4 — Question 4. Ribose and Deoxyribose and Their Phosphate Esters. (20 points) (a) The Haworth projection is shown of D-ribose. This ribose is _______ (alpha, beta, gamma) at the anomeric carbon. Ribose is a _______ (aldose, ketose). Ribose is a _______ (triose, tetrose, pentose, hexose). (10 points) Cyclic D-ribose Fischer Projection of Fischer Projection of Acyclic D-ribose Acyclic L-ribose (b) Draw the Haworth projection of the nucleoside cytidine; i.e., draw the Haworth projection of D-ribose and add the nucleobase cytosine in the correct fashion. (6 points) (c) Draw the Haworth projection of the nucleotide 3’-monophosphate cytidine. [The points for (c) all are given for the proper respresentation of the connection of the phosphate and the ribose.] (4 points) — 5 — Question 5. Single and Double Strands of DNA. (20 points) (a) The skeleton of the AT base pair is shown. The R-groups are shown where adenine and thymine are attached to the sugar moieties of the backbones. Complete the structures of A and T by adding all double bonds, lone pairs, formal charges, etc. Indicate hydrogen bonds as dashed lines. (8 points) (b) A piece is shown of the _G base pair in ds-DNA. (1) Complete the drawing of the backbones on both sides by adding all double bonds and formal charges to the phosphate groups. (2) Complete the drawing of the purine nucleobase by adding all double bonds and lone pairs. (3) Add the complete structure of the respective pyrimidine nucleobase (the six-membered ring is outlined). (4) Indicate hydrogen bonds as dashed lines. (12 points) — 6 — .
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