Ribosomal RNA (rRNA)
A class of RNA found in the ribosomes of cells.
2. The RNA molecules that are the structural components of the ribosomal subunits. In prokaryotes, the rRNA molecules are 23S, 16S, and 5S; in eukaryotes they are 28S, 18S, 5.8S, and 5S.
3. The kind of RNA that constitutes the ribosomes and provides the site for translation.
4. Ribosomal RNA; the RNA subunits that, together, compose a ribosome

Ribosomes
Small cellular components composed of specialized ribosomal RNA and protein; site of protein synthesis.
2. A cytoplasmic organelle composed of RNA and protein that is the site of protein synthesis
3. The site of protein synthesis (or translation) in the cell, mainly consisting of ribosomal RNA

Ring Species
A situation in which two reproductively isolated populations (see reproductive isolation) living in the same region are connected by a geographic ring of populations that can interbreed.

RNA (Ribonucleic acid)
A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell. The structure of RNA is similar to that of DNA. There are several classes of RNA molecules, including messenger RNA, transfer RNA, ribosomal RNA' and other small RNAs, each serving a different purpose.
2. A nucleic acid formed upon a DNA template using ribose instead of deoxyribose.
3. Nucleic acid characterized by the presence of the base uracil instead of thymine, and by the sugar ribose instead of deoxyribose. RNA is usually single-stranded, and is genera by transcription from DNA. There are several types: messenger RNA, ribosomal RNA, and transfer RNA.
4. Ribonucleic acid. Messenger RNA, ribosomal RNA, and transfer RNA are its three main forms. These act as the intermediaries by which the hereditary code of DNA is converted into Proteins. In some viruses, RNA is itself the hereditary molecule.
5. Ribonucleic acid; any of a family of polynucleotides characterized by their component sugar ribose and one of their pyrimidines; ingle-stranded and have lower molecular weight than DNA.