**Question:** What are the components of a nucleoside?

**Core Concept:** Nucleosides are the building blocks of nucleic acids, particularly DNA and RNA. They are composed of three essential parts: a sugar, a phosphate group, and a nitrogenous base.

**Why the Correct Answer is Right:** A nucleoside consists of three components:
1. **Pyrimidine**: This is a type of nitrogenous base found in nucleosides, nucleotides, and nucleic acids. In DNA and RNA, pyrimidines are represented by cytosine, thymine, and uracil.
2. **Sugar**: Nucleosides contain a sugar molecule (deoxyribose in DNA and ribose in RNA). The sugar molecule is essential for the formation of nucleotides and, subsequently, nucleic acids.
3. **Purine**: Purines are another type of nitrogenous bases found in nucleosides, nucleotides, and nucleic acids. In DNA and RNA, purines are represented by adenine and guanine.

**Why Each Wrong Option is Incorrect:**

A. **Histone**: Histones are proteins that help to package and organize DNA into chromatin. They are not part of nucleosides.

B. **Purine**: While purines are part of nucleosides, this option is incorrect because it refers to the larger group of nitrogenous bases (adenine and guanine) and not the specific sugar component of nucleosides.

C. **Deoxyribose**: This option is incorrect because it refers to the sugar molecule in DNA, not nucleosides. Nucleosides contain both a sugar and a nitrogenous base.

D. **Phosphate**: Nucleosides contain a phosphate group as part of the nucleotide, not nucleoside itself.

**Correct Answer:** A nucleoside is made up of Pyrimidine (nitrogenous base), Sugar (deoxyribose in DNA or ribose in RNA), and Purine (nitrogenous base).