BR4 BS CBT FL error...

[MCAT guy]

---

Members do not see this ad.

has anyone else done BR4... the biology section passage III has an error:

The fragmentation caused by cyanogen bromide in Experiment I, plus the binding of cysteine by dabsyl chloride in Experiment II, tell you that the EXACT sequence of the polypeptide is known up to which amino acid?

Amino acid #7 C is the best answer. Cysteine is the first amino acid in the polypeptide sequence, as is evident from the dabsyl chloride binding. This confirms that the first three amino acids in the polypeptide are Cys-Thr-Met. Because cyanogen bromide cleaves after methionine, we know that the second fragment must end in methionine. Fragment A ends in methionine, so it must be the second fragment in the polypeptide sequence. The second fragment has the sequence from amino terminal to carboxyl terminal of Ser-Lys-Gly-Met. This sets the first seven amino acids in the polypeptide from amino terminal to carboxyl terminal as: Cys-Thr-Met-Ser-Lys-Gly-Met. As far as the last four amino acids are concerned, there is no way from the information given to know the order of the last fragment from amino terminal to carboxyl terminal. This means that the sequence is known only up to Amino acid #7.

They've made an assumption here that the enzyme cuts only 1 amino acid. There is no logical way to come to their conclusion without an assumpption and the passage didn't state that it only cleaves one amino acid.

BR bio asks a lot of random fact stuff too I've noticed. I've been getting owned on these but on AAMC bio is my better section. weird.