This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2018, Subject name: Biochemistry
Klenow fragment is formed by loss of fragment having which activity: 
Select and explain. 
A. 5'- 3' polymerase, B. 3'- 5' exonuclease, C. 5'- 3' exonuclease, D. 3'- 5' polymerase
C: 5'- 3' exonuclease
Answer: C: 5'- 3' exonuclease 
Explanation: Klenow fragment Large fragment produced by Subtilisin mediated proteolytic cleavage of E.Coli DNA polymerase I. Proteolysis removes the 5' -->3' exonuclease activity from N-terminal. Klenow fragment - Functions : Remove 3' overhang Fills 5' overhangs Synthesis of double-stranded DNA from single-stranded templates Preparation of radioactive DNA probes Was used in PCR