Biochemistry Exam Study Guide/BMC23

University of Wisconsin School of Medicine and Public Health Biochemistry Exam 2 Study Guide BMC23

A) This result indicates one of two things.   1) The intron that is now expressed in the protein contains a stop codon. 2) The intron that is now expressed has a number of base pairs not divisible by 3 changing the reading frame of exon 2 and creating a stop codon in the early part of exon 2. Both result in early termination of the polypeptide making it shorter.

B) Since less polypeptide is made but is normal in structure we can infer that the mRNA is not as stable and does not last as long to have many polypeptides made.  Therefore, the additonal 3' UTR mus have a destabilization factor causing normal structure synthesis of the polypeptide, but at a reduced level.

C) The asterisk is very close to the beginning of the translated region of Exon 1 and causes a 30 AA shorter peptide.  Therefore it is likely the the AUG codon has been changed.  Due to this change the ribosome goes 30 codons further to find another AUG which is why the polypeptide is 30 AA's shorter.  The reason for the change in the localization of this protein is that the 30 AA's that were skipped in translation contained a signal sequence.  Without this sequence the protein never hooks up with the ER and just hangs out in the cytoplasm forever.