Correct option is B
Statement A: "Alkaline phosphatases remove 3’ phosphates from DNA and RNA." (Incorrect)
- Alkaline phosphatases (e.g., calf intestinal phosphatase, CIP) remove 5' phosphates, not 3' phosphates, from DNA and RNA.
- This enzymatic activity is used to prevent self-ligation of DNA fragments during cloning procedures.
- Since the statement specifies 3’ phosphates, it is incorrect.
Statement B: "S1 nuclease removes single-stranded regions from partially double-stranded DNA." (Correct)
- S1 nuclease is a single-strand-specific endonuclease that cleaves single-stranded DNA (ssDNA) and RNA.
- It is commonly used in molecular biology to digest ssDNA overhangs in partially double-stranded DNA molecules.
- It also plays a role in the processing of DNA and RNA hybrids.
- Since this enzyme removes single-stranded regions in partially double-stranded DNA, this statement is correct.
Statement C: "5’ end-labeling of DNA molecules can be done by using polynucleotide kinase which transfers a ³²P-labeled phosphate group to the 5’ end of dephosphorylated DNA." (Correct)
- Polynucleotide kinase (PNK) catalyzes the transfer of a phosphate group from ATP to the 5' hydroxyl (OH) group of DNA or RNA.
- This process is used for radioactively labeling DNA or RNA fragments at their 5’ ends (³²P-labeling is a classic method).
- Since this is an accurate description of the function of PNK, the statement is correct.
Statement D: "3’-5’ exonuclease activity of Taq polymerase releases the reporter from the 3’ end of TaqMan probes in qPCR." (Incorrect)
- Taq polymerase lacks 3’-5’ exonuclease activity; instead, it has 5’-3’ exonuclease activity.
- In TaqMan qPCR, Taq polymerase degrades the TaqMan probe during extension, releasing the fluorescent reporter. However, this is due to its 5'-3' exonuclease activity, not 3’-5’.
- Since the statement incorrectly describes the activity of Taq polymerase, it is incorrect.
