# Cell Structure and Cell Organelles

## Ribosomes

Ribosomes usually consist of two subunits that form an interlocked structure. Each component is made of 1-2 very large RNA molecules (ribosomal RNA, rRNA) and several smaller protein units. Ribosomes are found in all cells, as well as in mitochondria and chloroplasts. They play an important role in the translation of DNA to RNA-transcribed messenger RNA (mRNA) and in the synthesis and secretion of proteins. Ribosomes may be bound to the endoplasmic reticulum or be free in the cytoplasm.

Fig.1
Ribosomes

The protein factories of the cell.

Ribosomes consist of a larger and a smaller subunit. Both parts contain rRNA and associated proteins.

Higher cells have between 105 and 107 ribosomes with a diameter of 25 $nm$.

Eukaryotes have free ribosomes in the cytoplasm in addition to membrane-bound ribosomes that are attached to the rough endoplasmic reticulum (ER).

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