Cleaving amino acid sequences

[cloak25]

Given that that pepsin cleaves Phe, Trp, Tyr, Asp, Glu, and Leu at the carboxyl end and Thermolysin cleaves Leu, Ile, and Val at the amino end.

If the separate treatment of a protein first with pepsin and then with thermolysin generated the same polypeptides, then which of the following peptide linkages is present in the protein?

A. Ile-Phe
B. Leu-Leu
C. Tyr-Val
D. Val-Met

Answer: C

I don't get what the question is trying to ask. Any help is appreciated! thanks. The question is from TBR ochem book II section VII passage XI #80 if anyone wants to know.

---

Members don't see this ad.

 

[chiddler]

Given that that pepsin cleaves Phe, Trp, Tyr, Asp, Glu, and Leu at the carboxyl end and Thermolysin cleaves Leu, Ile, and Val at the amino end.

If the separate treatment of a protein first with pepsin and then with thermolysin generated the same polypeptides, then which of the following peptide linkages is present in the protein?

A. Ile-Phe
B. Leu-Leu
C. Tyr-Val
D. Val-Met

Answer: C

I don't get what the question is trying to ask. Any help is appreciated! thanks. The question is from TBR ochem book II section VII passage XI #80 if anyone wants to know.

If a sequence is cut and generates the same pieces, what arrangement must be present?

So lets write out the sequence of amino acids including the N and C ends, such as N-Ile-C-N-Phe-C. Lets see if this works.

A. N-Ile-C N-Phe-C

pepsin cleaves Phe at the C end, and the thermolysin at the N end. So this doesn't work because two different fragments will be generated.

B. Same.

C. N-Tyr-C N-Val-C

Pepsin cleaves Tyr at the C end, and thermolysin at the N end. That is the exact same site in both enzymes! Therefore, this sequence must be present.

 

[kasho11]

Yeah, it's just saying if separate treatments with two different peptide cleaving enzymes yields the same peptides, one at the C terminus and one at the N terminus, there must be a linkage where they both cleave.

 

[MedPR]

Yeah, it's just saying if separate treatments with two different peptide cleaving enzymes yields the same peptides, one at the C terminus and one at the N terminus, there must be a linkage where they both cleave.

And what linkage they both won't cleave. I read this section for the first time the night before my MCAT and I thought it really interesting. Thankfully I read it, because it popped up on the real thing.

 

[chiddler]

And what linkage they both won't cleave. I read this section for the first time the night before my MCAT and I thought it really interesting. Thankfully I read it, because it popped up on the real thing.

oh nice!

what topic, exactly? i don't understand what you mean by "and what linkage they won't cleave".

 

[pfaction]

That's not how I interpreted the question so I got ****ing rocked on this question. I thought, it was saying, you put the protein in pepsin, and THEN in the other thing.

 

[chiddler]

Are amino acid sequences always written N to C similar to how DNA is written 5 to 3?