| Journey into the Cell: Ribosomes | |||||
What are ribosomes? Ribosomes are responsible for assembling the proteins of the cell. Ribosomal subunits are synthesized by the nucleolus. Depending on the protein production level of a particular cell, ribosomes may number in the millions. 
Ribosome attached to endoplasmic reticulum, Image courtesy of The Virtual Cell. What are their distinguishing characteristics? Ribosomes are typically composed of two subunits: a large subunit and a small subunit. These two units join together when the ribosome attaches to messenger RNA to produce a protein in the cytoplasm (cyto-). 
Small and large ribosome subunits, Image courtesy of The Virtual Cell. There are two places that ribosomes usually exist in the cell: suspended in the cytosol and bound to the endoplasmic reticulum. These ribosomes are called free ribosomes and bound ribosomes respectively. In both cases, the ribosomes usually form aggregates called polysomes (poly-) (also known as polyribosomes). 
Liver cell ribosomes and polyribosomes, Copyright Dennis Kunkel. Free ribosomes usually make proteins that will function in the cytosol, while bound ribosomes usually make proteins that are exported or included in the cell's membranes. Interestingly enough, free ribosomes and bound ribosomes are interchangeable and the cell can change their numbers according to metabolic needs. Share Your Opinions What do you think about the cell's ribosomes? What are the advantages to having ribosomal protein production? Are there any disadvantages? Come on over to the Biology Forum and share your thoughts, opinions and feelings. Until next time... | |||||
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