Chapter 20 - The Regulation of Gene Expression Chapter 20, Question 11 Mitotic c

Question

Chapter 20 - The Regulation of Gene Expression Chapter 20, Question 11 Mitotic cyclin is an example of a protein that is selectively degraded at a particular point in the cell cycle, namely the onset of anaphase. Suppose that you use recombinant DNA techniques to create a mutant form of mitotic cycin that is not degraded at the onset of anaphase Part A Sequence analysis of the mutant mitotic cyclin shows that it is missing a stretch of nine amino acids near one end of the molecule. Based on this information, discuss the possible explanations of why this form of mitotic cyclin is not degraded at the onset of anaphase. Select all that apply. The removal of a stretch of amino acids could change the conformation of ubiquitin so that it can no longer form the ubiquitylating enzyme complex The missing stretch of amino acids contains the lysine to which ubiquitin is normally attached when mitotic cyclin is being targeted for destruction. The missing stretch of amino acids contains the cysteine to which ubiquitin is normally attached when mitotic cyclin is being targeted for destruction The missing segment contains a proteasome whose detection by an appropriate recognition protein normally targets mitotic cyclin for ubiquitylation The missing segment contains a degron whose detection by an appropriate recognition protein normally targets mitotic cyclin for ubiquitylation The removal of a stretch of amino acids could change the conformation of mitotic cyclin so that it can no longer serve as a substrate for the ubiquitylating enzyme complex. Previous Answers Correct

Explanation / Answer

Here the first thing we can do for distinguish the first 2 possible explanations is to get the amino acid sequence of the ubiquitylation size of normal mitotic cyclin and put special attention in the part of the sequence corresponding to the missing stretch of nine amino acids of the mutant cyclin looking for the lysine that is attached to ubiquitin when mitotic cyclin is being targeted for destruction and also looking for a degron sequence whose recognition by a protein could targets mitotic cyclin for ubiquitylation (the first two possible explanations).

And for testing the third explanation we can use x-ray spectroscopy to determine the conformation of both normal and mutant cyclin and see if the removal of the stretch of nine amino acids changed the spatial conformation of the mutant cyclin in relation with the normal cyclin.

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