This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Which of the following enzymes in DNA dependent RNA polymerase? 
Select and explain. 
A. DNA ligase, B. Primase, C. DNA polymerase III, D. RNA transcriptase
B: Primase
Answer: B: Primase 
Explanation: DNA primase is an enzyme involved in the replication of DNA and is a type of RNA polymerase. Primase catalyzes the synthesis of a sho RNA (or DNA in some organisms ) segment called a primer complementary to a ssDNA template. Primase is of key impoance in DNA replication because no known replicative DNA polymerases can initiate the synthesis of a DNA strand without an initial RNA or DNA primer (for temporary DNA elongation). After this elongation, the RNA piece is removed by a 5&; to 3&; exonuclease and refilled with DNA.