This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anatomy
True statement about Ribozyme 
Select and explain. 
A. RNA molecular that acts catalytically to change itself or another RNA molecule, B. t-RNA, C. m-RNA, D. Ribosome
A: RNA molecular that acts catalytically to change itself or another RNA molecule
Answer: A: RNA molecular that acts catalytically to change itself or another RNA molecule 
Explanation: The substrate for ribozymes is often an RNA molecule, and it may even be pa of the ribozyme itself Ribozymes vary greatly in size. A self-splicing group I intron may have more than 400 nucleotides. The hammerhead ribozyme consists of two RNA strands with only 41 nucleotides in all. As with protein enzymes, the three-dimensional structure of ribozymes is impoant for function. Ribozymes are inactivated by heating above their melting temperature or by addition of denaturing agents or complementary oligonucleotides, which disrupt normal base-pairing patterns. Ribozymes can also be inactivated if essential nucleotides are changed. Example: Hammerhead ribozyme: These segments are called hammerhead ribozymes because their secondary structures are shaped like the head of a hammer. The hammerhead ribozyme is a metalloenzyme; Mg+2 ions are required for activity. The phosphodiester bond at the site of self-cleavage is indicated by an arrow In Tetrahymena, the pre-rRNA molecule contains an intron that is removed by self-splicing (in the presence of guanosine, GMP, GDP or GTP) without the need for involvement of any protein. This was the first ribozyme discovered but many have since been repoed.