system
Given the following post, respond as if you're commenting on Reddit:
human
What does RNA primer have that DNA Polymerase-III doesn't that allows it to start complementary nucleotide base-pairing with the template strand of DNA?

What the textbooks say is that DNA Polymerase-III, by itself, can't begin arranging the complementary base pairs in a replicating DNA strand. What is needed first is an RNA primer, that acts to place a few nucleotides to the strand being synthesized, and THEN DNA pol-III will begin adding nucleotides to the 3' end of this newly created primer.

But, how is it that RNA primer **can** add nucleotides "from scratch" and DNA pol-III can't?

edit: Wow, many thanks for all the helpful replies. Sorry for the confusion - I DID mean RNA primase, instead of primer!
gpt
Cells make many copies of RNA, so it doesn't need to be extremely accurate. On the other hand, mistakes in DNA are long-term, so DNA polymerase needs to have a high degree of accuracy (referred to as fidelity). When adding a base to a strand, the new base pairs with its complementary base before the polymerase catalyzes the addition (this ensures the high fidelity). The key, though, is that pairing between bases is stabilized by the pairing of the neighboring bases.

The first few bases of the primer are often not added correctly, which is why the cell uses RNA primers--if it were a DNA primer, there would be no way of determining which bases to excise, other than through the normal proofreading techniques.

(I am a PhD student in medicinal chemistry, and have taken classes on nucleic acids as well as biology and biochemistry)