Chemistry 2050 “Introduction to Organic ” Fall Semester 2011 Dr. Rainer Glaser

Examination #5: The Final “Lipids, , Nucleobases & DNA.”

Monday, December 12, 2011, 10 am – 12 pm.

Name: Answer Key

Question 1. Lipids and Detergents. 20 Question 2. and Carbohydrates. 20 Question 3. Nucleobases of DNA and RNA. 20 Question 4. and 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, H3C−(CH2)16−COOH, and one molecule of the unsaturated fatty acid oleic acid, H3C−(CH2)7−CH=CH−(CH2)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 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. (8 points)

— 2 — Question 2. Glyceraldehyde and Carbohydrates. (20 points)

(a) The structure shown is the ____ (R, S) enantiomer of glyceraldehyde.

Mark the chiral 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-______(, ). Draw the corresponding on the right. (4 points)

(c) Draw the Fischer projection of D-ribose. The molecular formula of ribose is C5H10O5. Ribose is an ______(, ). (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 (NH2) 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 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 ______(, tetrose, pentose, ). (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 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)

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