2007-03-11 23:06:54 · 3 answers · asked by teck kim 2 in Science & Mathematics ➔ Biology
DNA polymerase cannot start working from scratch. It needs a primer with a 3'OH group onto which it can attach a dNTP. DNA polymerase is what is called a holoenzyme which is a group of several different protein subunits. This molecule also makes sure that the right base is inserted.
Primase is the enzyme that attaches a small RNA primer to the single-stranded DNA to act as a substitute 3'OH to allow DNA polymerase to begin. This RNA primer is eventually removed by RNase.
2007-03-12 02:03:50 · answer #1 · answered by ATP-Man 7 · 0⤊ 0⤋
Because the DNA polymerase can only add to an existing 3'OH group, and initially there is no such group available. By contrast, RNA polymerase can insert a base even though there is noting to attach to. So, the primer is RNA, which leaves a free 3'OH group, thus allowing DNA polymerase to start adding bases.
2007-03-12 07:33:41 · answer #2 · answered by Pierian 4 · 1⤊ 0⤋
How would the enzyme know where to start. DNA polymerase can only add nucleotides to an existing strand. That means they can't just go anywhere and start dropping nucleotides.
2007-03-12 06:17:26 · answer #3 · answered by Anonymous · 1⤊ 0⤋