Chemistry2050 IntroductiontoOrganicChemistry FallSemester2011 Dr.RainerGlaser Examination #5: The Final Lipids, Carbohydrates, Nucleobases & DNA. Monday, 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 distearoleate. This fat is the _TRI-ester formed between one molecule of the triol GLYCEROL_, two molecules of the fatty acid stearic acid, H 3 C (CH 2 ) 16 COOH, and one molecule of the unsaturated fatty acid oleic acid, H 3 C (CH 2 ) 7 CH=CH (CH 2 ) 7 COOH. In your drawing, attach the oleic acid to one of the primary alcohols of the triol. Clearly indicate whether the alkene in oleic acid is cis or trans. To convert this fat into soap, one would cook the fat with aqueous NaOH solution, a process that is called SAPONIFICATION. (12 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 headgroup 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. (8 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. 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-ribose. The molecular formula of ribose is C 5 H 10 O 5. Ribose 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 Occurs in DNA: Yes Yes Yes Yes Occurs in RNA: Yes Yes Yes NO Is a Purine Derivative: Yes Yes NO NO Is a Pyrimidine Derivative: Yes Yes Yes Yes Contains an Amino (NH 2 ) Group: Yes Yes Yes NO Contains an Imidazole: Yes Yes NO NO Contains a Cyclic Amide: NO Yes Yes Yes Base-Pairs with: T C G A (b) Tautomers of Nucleobases. Thymine is a tautomer of 2,4-dihydroxy-5-methylpyrimidine. 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-2-deoxyribose. This deoxyribose is (alpha, beta, gamma) at the anomeric carbon. 2-Deoxyribose is a (aldose, ketose). Deoxyribose is a (triose, tetrose, pentose, hexose). (10 points) Cyclic D-2-deoxyribose Fischer Projection of Acyclic D-2-deoxyribose (b) Draw the Haworth projection of the nucleoside adenosine; i.e., draw the Haworth projection of D-2-deoxyribose and add the nucleobase adenine in the correct fashion. (6 points) (c) Draw the Haworth projection of the nucleotide 5 -monophosphate 2 -deoxyadenosine. [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 GC base pair is shown. The R-groups are shown where guanine and cytosine are attached to the sugar moieties of the backbones. Complete the structures of G and C 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 CG 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 pyrimidine nucleobase by adding all double bonds and lone pairs. (3) Add the complete structure of the respective purine nucleobase (the bicyclic skeleton is outlined). (4) Indicate hydrogen bonds as dashed lines. (12 points) 6