This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which one of the following sequence is not expressed in a mature messenger RNA of a segment of a eukaryote gene? 
Select and explain. 
A. Intron, B. Exon, C. Plasmid, D. TATA box
A: Intron
Answer: A: Intron 
Explanation: In eukaryote organisms, a structural gene usually consists of several coding regions which are known as exons that are separated by non-coding regions which are introns / intervening sequences. They do not express. Ref: Human Molecular Biology: An Introduction to the Molecular Basis of Health and Disease, 2003, Page 41