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 radioisotope labeled molecule is used to find out rate of DNA synthesis? 
Select and explain. 
A. Thymidine, B. Thymidine, C. Adenine, D. Adenine
A: Thymidine
Answer: A: Thymidine 
Explanation: Ans. is 'a' i.e., Thymidine One application of isotope labeling would be in measuring DNA synthesis, that is cell proliferation in vitro. uses - thymidine labeling to compare pattern of synthesis (or sequence) in cells.