This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
RNA primer in eukaryote is formed by ? 
Select and explain. 
A. Ligase, B. RNA polymerase, C. Topoisomerase, D. Helicase
B: RNA polymerase
Answer: B: RNA polymerase 
Explanation: DNA synthesis cannot commence with deoxyribonucleotides because DNA polymerase cannot add a mononucleotide to another mononucleotide.Thus, DNA polymerase cannot initiate synthesis of complementary DNA synthesis strand of DNA on a totally single stranded template.For this, they require RNA primer, which is a sho piece of RNA formed by enzyme primase (RNA polymerase) using DNA as a template.RNA primer is then extended by addition of deoxyribonucleotides.Later on, the ribonucleotides of the primer are replaced by deoxyribonucleotides. Primase is actually a DNA primase which has RNA polymerase activity. This DNA primase is also called DNA polymerase.