BRAINCAKERibosomes
Ribosomes are the sites of protein synthesis. They are very small (about 20 to 25 nm across), so they can only be seen with an electron microscope, where they appear as tiny dark dots. They are not surrounded by a membrane.
Structure
Each ribosome is made of ribosomal RNA (rRNA) and protein, arranged in two subunits: a large subunit and a small subunit. In eukaryotic cells, the subunits are made in the nucleolus and leave the nucleus through the nuclear pores.
80S and 70S ribosomes
Ribosomes are classified by how fast they settle when spun in a centrifuge, measured in Svedberg units (S). Larger ribosomes have a larger S value.
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Key terms in this lesson
- translation
- The synthesis of a polypeptide at a ribosome, in which the sequence of codons on mRNA sets the order in which amino acids are joined.
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