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Chapter 7: Bioorganic Chemistry
367. (A) All the rings are “locked.” It is necessary for the ring to open (making the alde-
hyde accessible) for the sugar to be reducing.
368. (D) The anomeric carbon atom in unit A is farthest to the right in the ring. The ano-
meric carbon atom in unit D is the “top” one (connected to unit B). An acetal is R2C(OR)2, 
and a hemiacetal is R2C(OR)OH (the R groups may or may not be the same).
369. (D) Each ring is one unit of unsaturation, and each double bond is another.
370. (D) Maltose is a disaccharide, but all the subunits are monosaccharides.
371. (B) Unit D is the β-anomer. The anomeric carbon in unit D is 1. The connection of 
unit D to unit B is to carbon 2 in unit B (numbering from the anomeric carbon 1). This 
combination is B.
372. (C) The structure of the hexapeptide is gly-ala-ser-gly-ser-pro. The 2,4-dinitrofluo-
robenzene might react with either end; however, since it is with the gly, it must react with 
the N-terminal amino acid.
373. (A) The gly is terminal because of the reaction with 2,4-dinitrofluorobenzene; there-
fore, one of the first two tripeptide fragments must be the N-terminus. There is only one 
ala residue; therefore, the first and last tripeptide residues must overlap, with the ala being 
the same in each. These tripeptides now give the sequence gly-ala-ser-gly, so the C-terminal 
gly must be the gly in the remaining tripeptide. Combining the third tripeptide gives the 
answer. The dipeptides can be used to check the prediction. All structures follow the con-
vention of listing from N-terminus to C-terminus.
374. (A) The presence of the electron-withdrawing nitro groups makes the aromatic ring 
very electrophilic. The amine end of the octapeptide is a stronger nucleophile than the acid 
end of the octapeptide. The stronger nucleophile attacks the electrophile. 
375. (B) To determine the absolute configuration about a carbon atom, note the lowest-
priority group and assign priority to the other groups. Beginning with the highest-priority 
group (N), count toward the next highest group and end with the lowest group. Counting 
to the right (clockwise) is R, and counting to the left (counterclockwise) is S. The configu-
ration about each carbon atom is independent of the configuration about the other carbon 
atom. Doing this, the counting is counterclockwise, or an S configuration.
376. (C) Amino acids are considered to be amphoteric because they can behave as both an 
acid and a base. They have a carboxylic acid end that can act as a proton donor (acid) and 
an amine end that can act as a proton acceptor (base). 
377. (A) This is a linkage between carbon 1 (on the left-hand glucose ring) of the α-anomer 
and the carbon 4 on the other ring.