What types of ribosomes are found in eukaryotic cells?
Eukaryotic cells primarily contain 80S ribosomes, found in the cytoplasm and rough endoplasmic reticulum. However, in certain organelles like mitochondria and chloroplasts, they contain 70S ribosomes, which are similar to those in prokaryotic cells. The 'S' stands for Svedberg units, referring to sedimentation rate in centrifugation.
The Role of Ribosomes in Eukaryotic Cells
Structure of Ribosomes:
Eukaryotic cells contain ribosomes of varying sizes based on their location within the cell. Primarily, they contain 80S ribosomes in the cytoplasm and rough endoplasmic reticulum, composed of a 40S small subunit and a 60S large subunit. However, within certain organelles such as mitochondria and chloroplasts, eukaryotic cells contain 70S ribosomes, similar to prokaryotic cells.
Function of Ribosomes:
The ribosome, a complex macromolecule, contributes to protein synthesis, and its subunits—the large and the small—are responsible for binding the mRNA template and tRNAs, respectively. Ribosomes dissociate into these subunits when not synthesizing proteins and reassociate during the initiation of translation. The complete mRNA/poly-ribosome structure is termed a polysome.
Svedberg Units:
Regarding the 'S' in 70S and 80S, it stands for Svedberg units, a measure of the rate of sedimentation in centrifugation rather than size. This unit considers not only the mass but also the shape and surface qualities of the molecules, which is why these values are not additive.