I. THE EUKARYOTIC CELL
A. COMPOSITION AND FUNCTIONS OF EUKARYOTIC CELLULAR STRUCTURES
5. Ribosomes
The overall purpose of this Learning Object is to learn the chemical makeup and the functions associated with the ribosomes in eukaryotic cells.
The cell is the basic unit of life. Based on the organization of their cellular structures, all living cells can be divided into two groups: prokaryotic and eukaryotic (also spelled procaryotic and eucaryotic). Animals, plants, fungi, protozoans, and algae all possess eukaryotic cell types. Only bacteria have prokaryotic cell types.
Eukaryotic cells are generally much larger and more complex than prokaryotic. Because of their larger size, they require a variety of specialized internal membrane-bound organelles to carry out metabolism, provide energy, and transport chemicals throughout the cell.
We will now look at the ribosomes of eukaryotic cells.
Ribosomes (def)
Ribosomes are composed of rRNA and protein and consist of 2 subunits. In eukaryotic cells, the subunits have densities of 60S and 40S ("S" refers to a unit of density called the Svedberg unit) and are composed of longer rRNA molecules and more proteins than the 50S and 30S subunits found in prokaryotic ribosomes. When the two ribosomal subunits join together during translation, they form a complete ribosome having a density of 80S.
The ribosomes are both attached to the endoplasmic reticulum and free in the cytoplasm. They serve as a workbench for protein synthesis, that is, they receive and translate genetic instructions for the formation of specific proteins or polypeptides.
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