Biochemistry › Regulating Protein Degradation
A polypeptide when treated with trypsin yielded the following fragments:
(AM) (SAK) (YMPLWGIR)
The same polypeptide treated with chymotrypsin yielded the following fragments:
(MPLW) (GIRAM) (SAKY)
Which of the following displays the original sequence of the polypeptide?
SAKYMPLWGIRAM
MPLWGIRAMSAKY
AMSAKYMPLWGIR
WGIRAMSAKYMPL
GIRAMSAKYMPLW
This problem requires knowledge of the endopeptidase properties. Trypsin cleaves after the amino acids lysine and arginine, and chymotrypsin cleaves after the amino acids phenylalanine, tyrosine, and tryptophan.
Using this information, the slashes below indicate where each enzyme cleaved the polypeptide.
(AM) (SAK)/ (YMPLWGIR)/ trypsin
(MPLW)/ (GIRAM) (SAKY)/ chymotrypsin
Because the (AM) and (GIRAM) fragments have no slash after M in both the first and second treatment, one can conclude that this piece is at the end of the polypeptide. The other two pieces are sequenced by realizing that S starts the (SAK) and (SAKY) fragments and is never found in the middle of a fragment.
Which of the following describes the unfolded protein response?
All of these answers
Stopping protein translation
Increasing amount of local chaperones
Targeting misfolded proteins for degradation by the 26S proteasome
Triggering cell death
There are 4 main steps in the unfolded protein response: (1) Translation of proteins is stopped, (2) Chaperones are recruited to the location of misfolded proteins, (3) Misfolded proteins are "tagged" with ubiquitin chains for degradation by the 26S proteasome, (4) if the above steps fail, the cell undergoes programmed cell death. Thus, all of the answers choices are affiliated with the unfolded protein response.