Question

Question 9

Analysis of the cellular structure of Chewbacca (a Wookie) showed that most of the basic cellular and molecular processes are the same between Wookies and humans, much as they are the same between humans and other closely related organisms. Many proteins are highly conserved and basic cellular metabolism is maintained. Interestingly, one new organelle is present, which researchers named the Wookiesome. Many of the proteins found within the Wookiesome have the eight amino acid sequence “HARRIEST”. You make a hypothesis that this region is important for organelle import.

(A) Design an experiment to indicate if “HARRIEST” is necessary for organelle import.

(B) Design an experiment to indicate if “HARRIEST” is sufficient for organelle import.

(C) Explain how it is possible that the sequence could be necessary but not sufficient.

4. Explain how it is possible that the sequence could be sufficient but not necessary

Answer 1

(A)

To determine if HARRIEST is necessary for organelle import, Wookie cells can be transformed with a mutant protein that is normally found inside the Wookiesome, with the HARRIEST peptide sequence deleted. If the HARRIEST sequence is necessary for transport into the Wookiesome, then such a mutant protein will not be transported into the Wookiesome and would be found in ectopic locations within the cell.

(B)

To determine if the HARRIEST sequence is sufficient for import into the Wookiesome, a protein not normally imported into the Wookiesome would be tagged with the HARRIEST peptide sequence. If HARRIEST is sufficient for import into the Wookiesome, then this protein, normally not found in the Wookiesome, would be imported into the Wookiesome.

(C)

A signal peptide could be necessary but not sufficient for import into the organelle if multiple signalling sequences are required for the protein to reach the subcellular localization, of which this is one. The lack of this signalling sequence would prevent the protein from reaching its destination subcellular localization.

(D)

A signal peptide could be sufficient but not necessary for import into an organelle if multiple pathways exist to import the protein into the organelle. In such a scenario, the protein is targetted to the organelle due to various different signalling pathways, and anyone of them can result in the correct targetting.