This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
All of the following require 5' capping except? 
Select and explain. 
A. mRNA for Histone, B. siRNA, C. tRNA of Alanine, D. U6 snRNA
C: tRNA of Alanine
Answer: C: tRNA of Alanine 
Explanation: tRNA of Alanine does not require 5' capping. Capping process protects the 5' end of mRNA from the action of exonucleases and polyadenylation protects the 3' end of the mRNA. All mRNA, snRNA, and siRNA undergo this process, but tRNA are comparatively stable and do not require a capping at the 5' end. Reference: Harpers illustrated biochemistry 30th edition