What would you expect to happen if the anaphase-promoting complex/cyclosome (APC/C) failed to ubiquitinate securin?

Question

A.  The cohesin complex will be destroyed, and the cell will remain in metaphase.
B.  The cohesin complex will persist, preventing the cell from entering anaphase.
C.  Separase will be marked for degradation by securin, preventing the cell from entering anaphase.
D.  Securin will remain intact and therefore will degrade cohesin, allowing the cell to enter anaphase.

Clarify Question
  · What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

  Gather Content
  · What do you know about securin? How does it relate to the question?

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?

  Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

  Reflect on Process
  · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  The cohesin complex will persist, preventing the cell from entering anaphase.

Clarify Question
  · What is the key concept addressed by the question?
        o The question asks about the role of securing in the cell cycle.
· What type of thinking is required?
        o You are being asked to analyze several statements predicting what would happen in a cell if APC/C failed to ubiquitinate securin.
· What key words does the question contain and what do they mean?
        o Ubiquitinate securin – when ubiquitin is added to a protein, that protein is targeted for degradation.  

  Gather Content
  · What do you know about securin? How does it relate to the question?
        o Securin is an inhibitor of the enzyme separase.  Separase will cleave the cohesin complex that holds sister chromatids together.  Once cleaved, the sister chromatids can separate in anaphase.
        o APC/C ubiquitinates proteins and targets them for destruction.  If it cannot ubiquitinate securin, then securin will remain active.

  Consider Possibilities  
  · What other information is related to the question? Which information is most useful?
        o Securin is an inhibitor, not an enzyme so it cannot degrade separase or cohesin.
        o The cohesin complex needs to be destroyed for the cell to enter anaphase, so its destruction would not cause the cell to remain in metaphase.

  Choose Answer
  · Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Securin is an inhibitor of the enzyme separase.  Separase will cleave the cohesin complex that holds sister chromatids together.  Once cleaved, the sister chromatids can separate in anaphase.

  Reflect on Process
  · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question asked you to analyze several statements to choose which best explains what would happen if securin remained active in a cell. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you understand that ubiquitination of securin would lead to its destruction?  Did you recall that securin is an inhibitor of separase, and if securin was not degraded separase would remain inactive?  Did you predict that if separase remained inactive, cohesin would not be degraded and the sister chromatids could not separate allowing to cell to enter anaphase?