**Question:** RNA primer in eukaryote is formed by -

A. DNA polymerase
B. Ribonucleotide
C. Ribosome
D. RNase

**Core Concept:** In eukaryotic cells, the process of DNA replication involves a specialized RNA molecule called the RNA primer. This primer helps initiate the synthesis of DNA by providing a starting point for DNA polymerase, the enzyme that synthesizes DNA.

**Why the Correct Answer is Right:** The RNA primer is formed by an enzyme called RNase H, which is part of DNA polymerase III holoenzyme. RNase H cleaves the RNA strand from the DNA-RNA hybrid and degrades the RNA strand, leaving a 3'-OH group for DNA polymerase to add nucleotides and synthesize the new DNA strand.

**Why Each Wrong Option is Incorrect:**

A. DNA polymerase is the enzyme responsible for DNA synthesis, not RNA primer formation. DNA polymerase reads the DNA template strand and synthesizes the new DNA strand, but it does not form the RNA primer.

B. Ribonucleotide refers to a nucleotide containing a ribonucleoside monophosphate (RNMP) sugar. While ribonucleotides are components of RNA, they are not involved in forming the RNA primer. RNase is the enzyme responsible for RNA primer formation.

C. Ribosomes are the sites of protein synthesis in cells. They are not involved in RNA primer formation during DNA replication.

D. RNase H is the enzyme responsible for cleaving the RNA strand from the DNA-RNA hybrid and degrading the RNA primer. It does not form the RNA primer itself.

**Clinical Pearl:** Understanding RNA primer formation is crucial for understanding DNA replication in eukaryotic cells, as it is a fundamental process for genetic information maintenance and inheritance.

**Correct Answer:** D. RNase H

**Explanation:** RNase H is the enzyme responsible for cleaving the RNA strand from the DNA-RNA hybrid and degrading the RNA primer. This allows DNA polymerase to synthesize the new DNA strand, incorporating nucleotides complementary to the template DNA strand. This process ensures accurate replication of the genetic material and prevents the incorporation of incorrect nucleotides.