Exam 2 Essay

Submitted By rootew
Words: 1132
Pages: 5

CHM 461—Exam #2 A Name__________________________________
1 (10 pts) Assume that the sugar A = D-mannose.

A  B  C  D

Sugar B is the enantiomer of A
Sugar C is the C5-epimer of sugar B
Sugar D is the aldo-keto isomer of sugar C

a. Draw the Fischer structures of sugars A, B, C, & D.
b. Now draw the Haworth structure of the α-furanose form of sugar D.

2 (4 pts)The melting point of stearic acid is 70 °C. The structure of lactobacillic acid is shown to the right. Is the melting point of lactobacillic acid higher or lower than that of stearic acid ? Briefly explain your answer.

3 a. (4 pts) Give the name and abbreviation for the following molecule, and identify the specific linkage that is indicated by the arrow.

____________________________________________________ (name and abbreviation)

________________________________ (type of linkage)
4 (5 pts) Nucleotides are used for many things besides DNA and RNA. For instance, CDP-choline is the intermediate that is used to add the “polar head” to a diacylglycerol in the biosysnthesis of lecithin. Modify the structure of choline (given below) to draw the structure of CDP-choline. Scracth out any atom(s) you need to in order to connect choline to the rest of the molecule. Identify all phospoester and phosphoanhydride linkages in this structure.

5 (3 pts) Which of the following statements concerning the DNA double helix (“B form”) is not true?
a. The nucleotides are linked together by 3’-5’ phosphodiester bonds
b. The base pairs are “stacked” on the inside of the double helix
c. Each base pair is attached to adjacent base pairs by H-bond interactions
d. Each turn of the helix contains ~10 base pairs
e. There is a major groove and a minor groove where the edges of the base pairs are exposed and available for binding by various DNA-binding proteins

6 ( 5 pts) a Which structures from the Page O’ Structures are considered to be terpenes? Classify each one listed as a monoterpene, diterpene, triterpene, etc.?

b. Which of those structures actually is a bile salt ________________ and what about its structure allows it to perform its chief biological function?

7 (3 pts) Which of the following substances is most different from the other three?
a. ganglioside
b. cerebroside
c. phosphatidyl serine
d. sphingomyelin

8 (4 pts) In addition to lactose, how many other heterodisaccharides can D-galactose and D-glucose form?

9 (6 pts) The structure of sphingosine is given below. Using this structure as a foundation, draw the structure of a cerebroside (a glycosphingolipid) that contains an aldohexose that is not D-Glc. Scribble out the atoms on sphingosine that will be lost when the other components are linked to sphingosine to form the cerebroside. Identify by name the molecules that you add and identify the linkages that bond them to the sphingosine residue. (12 pt)

10 (8 pts) Raffinose is -D-Gal (1-6) -D-Glc (1-2) -D-Fru. It is a trisaccharide present in beans, broccoli, cabbage, etc. Humans do not possess an α-galactosidase enzyme necessary to break down raffinose. Thus, when ingested, it passes undigested through the stomach and small intestine. However, bacteria in the colon have the necessary enzymes to degrade and ferment raffinose to produce CO2, CH4 and/or H2 gasses - leading to the flatulence commonly associated with eating beans and other vegetables. Digestive aids such as Beano® contain an α-galactosidase.
a. Using Haworth Projections, draw the structure of raffinose.
b. Is raffinose a reducing sugar or non-reducing sugar?
c. Draw an arrow to the bond that is hydrolyzed by the α-galactosidase in Beano®.
d. Give the common and systematic names of the products