Cytosine (noun)

1. A nitrogenous base, one of the four that make up DNA and RNA, represented by the letter C.
2. A derivative of this base used in some chemical and biochemical processes.

Origin:

From the greek word kytos, meaning cell, and the suffix -ine, meaning belonging to or of the nature of.

Examples:

1. Cytosine is one of the building blocks of DNA and RNA.
2. The methylation of cytosine plays a crucial role in the regulation of gene expression.
3. Cytosine is paired with guanine in the DNA molecule.
4. The reaction between cytosine and uracil leads to the formation of a covalent bond.
5. Cytosine can be converted into another nitrogenous base, uracil, in a process known as deamination.