Nucleases are enzymes that degrade mRNA. In order for nuclease to overcome the inherent protections in mRNA that prevent its degradation, nucleases must use (Select all that apply.)A) 5' decapping enzymes.B) A and U sites that promote removal of the poly A tails.C) C and G recognition sites that activate removal of poly A tails.D) 3' end recognition sites that initiate quick degradation.E) 3' cap and poly A tail sites that activate degradation.

Question

What will be an ideal response?

Answer 1

A, B, D

Clarify Question
• What is the key concept addressed by the question? 
        o The question asks about degradation of mRNA. 
• What type of thinking is required? 
        o You are being asked to apply your knowledge of degradation of mRNA. 

Gather Content
• What do you know about degradation of mRNA? What other information is related to the question? 
        o Some mRNA contain specific sequences near their 3? ends that make them targets for enzymes that degrade mRNA. A sequence of A and U nucleotides near the 3? poly-A tail of a transcript promotes removal of the tail, which destabilizes the mRNA. Loss of the poly-A tail leads to rapid degradation by 3?-to-5? RNA exonucleases. Another consequence of this loss is the stimulation of decapping enzymes that remove the 5? cap, leading to degradation by 5?-to-3? RNA exonucleases. Other mRNA transcripts contain sequences near their 3? ends that are recognition sites for endonucleases, which cause these transcripts to be digested quickly. The short half-lives of the mRNA transcripts of many regulatory genes are critical to the function of those genes, because they enable the levels of regulatory proteins in the cell to be altered rapidly. 

Choose Answer
• Given what you now know, what information is most likely to produce the correct answer?  
        o mRNA 5' degradation can be stimulated by decapping enzymes, A and U sites that promote removal of the poly A tail and sequences near the 3' ends.  There is not a 3' cap on the mRNA. 

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 apply your understanding of degradation of mRNA. If you got the correct answer, great job! If you got an incorrect answer, where did the process break down? Did you recall that mRNA has a 5' cap and poly A tail?  Did you understand that some mRNA has a sequence that increases degradation?