CELL ORGANELLES: free ribosomes and polysomes (polyribosomes)

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ALL CELLS / Animal Cell : nucleus / nucleolus / nuclear envelope / nuclear pore / centrioles / cell membrane / microtubule / smooth endoplasmic reticulum / rough endoplasmic reticulum / ribosomes / polysomes / lysosome / peroxisome / mitochondrion / Golgi /

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ORGANELLE DIAGRAM: POLYSOMES or POLYRIBOSOMES: In this picture, ribosomes are seen floating free in the cytoplasm. Messenger RNA is threading into to some ribosomes at upper left and the two necklace-like arrangements represent polysomes (polyribosomes). Polysomes are variable in length and are strings of ribosomes joined by messenger RNA. As the mRNA feeds through these ribosomes, so proteins are synthesised. The proteins synthesised by these free ribosomes pass into the cytoplasm. (Proteins that are destined for the interior of the rough endoplasmic reticulum have a lead sequence that binds to the roughER. This links their associated ribosomes to the surface of the rER. Please see bound ribosomes.)

SUMMARY

• name(s): free ribosomes
• name(s): polysomes, polyribosomes
• location: free in cytoplasm
• appearance: approximately spherical bodies often arranged in strings or spirals (because they are strung together by messenger RNA).
• size: ribosomes are about 25nm in diameter
• function: synthesis of proteins

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