Respostas Questões 378-391

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378. (C) A dipeptide forms when two amino acids link, with water being released. This is 
not the case here, since this involves the linking of monosaccharides.
379. (D) There are 6 chiral carbon atoms present in the testosterone. The number of stereo-
isomers can be calculated by 2n, where n is the number of chiral carbons. Therefore, 26 = 64.
380. (B) Mutarotation is the term used to define this conversion. Anomerization is an 
artificial term. The remaining terms refer to other changes. 
381. (D) A pH of 7.4 indicates that the substance is slightly more basic than pure water, 
which has a pH of 7.0. A pH of 7.4 also means that the concentration of the hydrogen ion 
is less than the hydroxide ion concentration, so answer D is the correct answer.
382. (C) Since the leucine is immersed in a solution whose pH is the same as its isoelectric 
point, it will be in the zwitterion form, which has an overall 0 charge. Therefore, it will be 
attracted to neither electrode.
383. (A) An aldopentose is a sugar that has five carbons (pent = five Cs) and is an aldehyde 
(aldo = aldehyde). I and III fit those criteria; II has six carbons (hexose), and IV has no 
aldehyde present (ketose).
384. (D) If they formed smaller rings, there would be a great deal of strain introduced into 
the structure because the bond angles would be less than in a tetrahedral arrangement.
385. (C) The tertiary structure of proteins places the polar side chains on the exterior of 
the proteins, where they can interact with nearby molecules, such as water.
386. (B) A nucleoside is formed from a nitrogen base and a five-carbon sugar (no phos-
phate). A nucleoside can then react with phosphoric acid to form the phosphate ester, which 
is called a nucleotide. 
387. (A) Acid chlorides and acid anhydrides are extremely reactive species. They are far too 
reactive to exist in complex biological systems.
388. (A) The structure of the micelle is a conglomerate with the carboxylate groups (which 
are hydrophilic, or water loving) on the exterior and the nonpolar hydrocarbon tails (which 
are hydrophobic, or water hating) on the interior. Because of this, the solubility of the 
conglomerate is increased.
389. (C) Glycine is the only amino acid that does not have a chiral carbon. This is because 
the α-carbon has two hydrogen atoms attached to it, H2N-CH2-COOH.
390. (B) The isoelectric point of alanine is the average of the pKa values of the amine and 
carboxylic acid groups. The same two groups in ornithine will give about the same average 
as alanine; however, the additional –NH2 significantly increases the value.
391. (A) The ammonia is a nucleophile that attacks the carbonyl carbon atom.