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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. They are tiny round particles.

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-).

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).

free ribosomes usually make proteins that will function in the cytosol while bound ribosomes usually make proteins that are exported or included in the cells membranes. Interestingly enough, free ribosomes and bound ribosomes are interchangeable and the cell can change their numbers according to metabolic needs.

ribosomes - protein CONSTRUCTION TEAMS cells need to make proteins. Those proteins might be used as enzymes or as support for other cell functions. When you need to make proteins, you look for ribosomes. Ribosomes are the protein builders or the protein synthesizers of the cell. They are like construction guys who take one amino acid at a time and build long protein chains.

ribosomes could be in many places around the cell. You might find them floating in the cytoplasm. Those floating ribosomes make proteins that will be used inside of the cell. Other ribosomes are found on the endoplasmic reticulum. Endoplasmic reticulum with ribosomes attached is called rough. It looks bumpy under a microscope. Those attached ribosomes make proteins that will be used inside the cell and proteins made for export (outside the cell).

A ribosome is not just one piece. There are two pieces or subunits. Scientists named them 60-S and 30-S. When the cell needs to make protein, mrna is created in the nucleus. The mrna is then sent into the cell to the ribosomes. When it is time to make the protein, the two subunits come together and combine with the mrna. The two pieces lock onto the mrna and start the protein synthesis.

The process of making proteins is quite simple. We just explained that mrna is made in the nucleus and sent into the cell. The mrna combines with the ribosome subunits. Another nucleic acid lives in the cell - trna, which stands for transfer rna, and it is bonded to amino acids. With the mrna offering instructions, the ribosome connects to a trna and pulls off the amino acids. Slowly the ribosome makes a long amino acid chain that becomes a protein.