Question

If a junior scientist is setting up a DNA synthesis reaction in the lab and the deoxynucleotides are all gone, and he decides to use all the ribonucleotides, what will happen? Why?

1) The DNA synthesis reaction will proceed normally because ribonucleotides can substitute for deoxynucleotides.
2) The DNA synthesis reaction will not occur because ribonucleotides cannot substitute for deoxynucleotides.
3) The DNA synthesis reaction will proceed, but the resulting DNA will be different due to the presence of ribonucleotides.
4) The DNA synthesis reaction will not occur because ribonucleotides will inhibit the synthesis process.

Answer 1

The DNA synthesis reaction will not proceed because ribonucleotides contain a 2' OH group that is not compatible with DNA polymerases and thus cannot substitute for deoxynucleotides.

Step-by-step explanation:

If a junior scientist attempts to use ribonucleotides in a DNA synthesis reaction instead of deoxynucleotides, the reaction will not proceed as expected. This is because DNA polymerases, the enzymes responsible for DNA synthesis, require a free 3' hydroxyl group (OH) on the deoxynucleotide to form a phosphodiester bond with the incoming nucleotide.

Ribonucleotides contain a 2' OH in addition to the 3' OH, and this 2' OH group is not compatible with the enzymes that synthesize DNA. As a result, ribonucleotides cannot be used to substitute for deoxynucleotides, and the synthesis of DNA will not occur. In practical terms, using ribonucleotides where deoxynucleotides are required would result in an aborted DNA synthesis due to the structural differences between these molecules.