Cellular Biology

What are Ribosomes



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Ribosomes are a cellular component, that are not considered to be a true organelle because they lack a membrane, but are often referred to as a non-membranous organelle. They are found in the cytoplasm and are made of ribosomal RNA protein. Ribosomes, which are only around 20nm across, are vital in the production of new proteins, the fundamental building blocks used by cells throughout the body and across a wide variety of organisms for a wide variety of functions.




Ribosomes are made from two subunits with prokaryotic cells (such as bacteria) and eukaryotic cells (such as human cells) having ribosomes of differing size and mass. Although in each case there is a large subunit and a small subunit present. The two subunits of the ribosome fit together in a way that allows them to work together to translate a polypeptide chain from the messenger RNA in a process called protein synthesis.




However, despite the significant differences in size and mass, the actual core structure and functioning of the ribosome is largely the same in prokaryotic cells and eukaryotic cells. Having said this, what differences there are can be harnessed by chemists in their efforts to create antibiotics that are capable of destroying bacterial cells whilst not harming the cells of the patient.




The function of the ribosomes is in the translation of messenger RNA (mRNA) code which causes polypeptide synthesis as the process occurs. This is achieved by taking amino acids and catalyzing their assembly in a polypeptide chain. The binding together of amino acid sequences requires transfer RNA molecules which read the message on the messenger RNA. When several ribosomes are attached to a single mRNA this is called a polyribosome.




Ribosomes are found in several places in the cell. They are found in the cytosol, for example, which is the semi-fluid part of the cell's cytoplasm. These so-called free ribosomes can move around throughout the cytosol and the proteins that they produce can be used by the cell for a wide variety of activities.




They can also be found attached to the membrane of the rough endoplasmic reticulum, for example. Indeed it is the presence of the ribosomes that give the rough endoplasmic reticulum its rough appearance. Ribosomes are also found bound to other membranes such as to the nuclear envelope. Membrane-bound ribosomes typically deliver proteins that are either aimed at use in the cell membrane that they are attached to itself or else are going to be removed from the cell altogether by exocytosis.

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