are ribosomes membranous
Ribosomes are organelles composed of ribosomal proteins (riboproteins) and ribonucleic acids (ribonucleoproteins). The word ribosome is made from taking ‘ ribo ’ from ribonucleic acid and adding it to ‘ soma ’, the latin word for body. Ribosomes are bound by a membrane but they are not membranous. They are found distributed all over the cytoplasm. In a eukaryotic cell ribosomes occur freely in the cytoplasm, attached to the surface of branches of endoplasmic reticulum (RER), in the matrix of organelles like mitochondria and chloroplasts. It is also found attached to the nuclear membrane and inside the nucleolus. Membrane-bound ribosomes are attached to a structure known as rough endoplasmic reticulum. Free and membrane-bound ribosomes produce different proteins. Whereas membrane-bound ribosomes produce proteins that are exported from the cell to be used elsewhere, free ribosomes produce proteins used inside the cell itself. Ribosomes are found in two locations in the cell. Free ribosomes are present in the cytosol, the watery fluid inside the cell and are not attached to any other structure. Membrane-bound ribosomes are attached to a structure known as rough endoplasmic reticulum. They are found distributed all over the cytoplasm. In a eukaryotic cell ribosomes occur freely in the cytoplasm, attached to the surface of branches of endoplasmic reticulum (RER), in the matrix of organelles like mitochondria and chloroplasts. Ribosomes are found ‘free’ in the cytoplasm or bound to the endoplasmic reticulum (ER) to form rough ER. In a mammalian cell there can be as many as 10 million ribosomes. Several ribosomes can be attached to the same mRNA strand, this structure is called a polysome. Ribosomes have only a temporary existence. In a eukaryotic cell ribosomes occur freely in the cytoplasm, attached to the surface of branches of endoplasmic reticulum (RER), in the matrix of organelles like mitochondria and chloroplasts. It is also found attached to the nuclear membrane and inside the nucleolus. Ribosomes that are found in eukaryotic cells are tiny, round organelles that generate proteins from mRNA. Ribosomes are composed of protein and ribosomal RNA. The structure of the ribosome is composed of two subunits. One of the subunits is larger than the other. Free ribosomes are present in the cytosol, the watery fluid inside the cell and are not attached to any other structure. Membrane-bound ribosomes are attached to a structure known as rough endoplasmic reticulum. Free and membrane-bound ribosomes produce different proteins. Ribosomes are formed in the cytoplasm of prokaryotic cells. In eukaryotic cells, they are formed most often in the nucleolus. Another difference between ribosomes of prokaryotes and eukaryotes is the structure of the ribosomes. Prokaryotes have 70S ribosomes, each consisting of a small (30S) and a large (50S) subunit.
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