Final answer:
No new nucleotides can be added to the DNA being replicated in vitro if the DNA lacks a free 3' hydroxyl group, as DNA polymerase requires it for adding nucleotides, halting DNA synthesis.
Step-by-step explanation:
If a researcher is attempting to replicate DNA in vitro and uses DNA that does not have a free 3' hydroxyl (3'-OH) group, the result would be that no additional nucleotides can be added to the replicating DNA strand.
This is because DNA polymerase requires a free 3'-OH group on the existing nucleotide to form a phosphodiester bond with the incoming deoxynucleotide triphosphate. Thus, in the absence of a free 3'-OH group, the chain elongation process will not occur, and DNA replication will be effectively blocked.
This principle is exploited in methods such as Sanger sequencing, where dideoxynucleotide triphosphates (ddNTPs) that lack the 3'-OH group are intentionally added to terminate DNA synthesis at specific points, allowing for the determination of the DNA sequence.