<P> The ribosome is a large and complex molecular machine that catalyzes the synthesis of proteins, referred to as translation . The ribosome selects aminoacylated transfer RNAs (tRNAs) based on the sequence of a protein - encoding messenger RNA (mRNA) and covalently links the amino acids into a polypeptide chain . Ribosomes from all organisms share a highly conserved catalytic center . However, the ribosomes of eukaryotes (animals, plants, fungi, and many unicellular organisms with a nucleus) are much larger than prokaryotic (bacterial and archaeal) ribosomes and subject to more complex regulation and biogenesis pathways . Eukaryotic ribosomes are also known as 80S ribosomes, referring to their sedimentation coefficients in Svedberg units, because they sediment faster than the prokaryotic (70S) ribosomes . Eukaryotic ribosomes have two unequal subunits, designated small subunit (40S) and large subunit (60S) according to their sedimentation coefficients . Both subunits contain dozens of ribosomal proteins arranged on a scaffold composed of ribosomal RNA (rRNA). The small subunit monitors the complementarity between tRNA anticodon and mRNA, while the large subunit catalyzes peptide bond formation . </P> <P> Compared to their prokaryotic homologs, many of the eukaryotic ribosomal proteins are enlarged by insertions or extensions to the conserved core . Furthermore, several additional proteins are found in the small and large subunits of eukaryotic ribosomes, which do not have prokaryotic homologs . The 40S subunit contains a 18S ribosomal RNA (abbreviated 18S rRNA), which is homologous to the prokaryotic 16S rRNA . The 60S subunit contains a 28S rRNA that is homologous to the prokaryotic 23S ribosomal RNA . In addition, it contains a 5.8 S rRNA that corresponds to the 5' end of the 23S rRNA, and a short 5S rRNA . Both 18S and 28S have multiple insertions to the core rRNA fold of their prokaryotic counterparts, which are called expansion segments . For a detailed list of proteins, including archaeal and bacterial homologs please refer to the separate articles on the 40S and 60S subunits . Recent research suggests heterogeneity in the ribosomal composition, i.e., that the stoichiometry among core ribosomal proteins in wild - type yeast cells and embryonic stem cells depends both on the growth conditions and on the number of ribosomes bound per mRNA . </P> <Table> <Tr> <Th> </Th> <Th> </Th> <Th> Eukaryotic </Th> <Th> Bacterial </Th> </Tr> <Tr> <Th> Ribosome </Th> <Td> Sedimentation coefficient </Td> <Td> 80 S </Td> <Td> 70 S </Td> </Tr> <Tr> <Td> Molecular mass </Td> <Td> ~ 3.2 × 10 Da </Td> <Td> ~ 2.0 × 10 Da </Td> </Tr> <Tr> <Td> Diameter </Td> <Td> ~ 250 - 300 Å </Td> <Td> ~ 200 Å </Td> </Tr> <Tr> <Th> Large subunit </Th> <Td> Sedimentation coefficient </Td> <Td> 60 S </Td> <Td> 50 S </Td> </Tr> <Tr> <Td> Molecular mass </Td> <Td> ~ 2.0 × 10 Da </Td> <Td> ~ 1.3 × 10 Da </Td> </Tr> <Tr> <Td> Proteins </Td> <Td> 47 </Td> <Td> 33 </Td> </Tr> <Tr> <Td> rRNAs </Td> <Td> <Ul> <Li> 28 S rRNA (3354 nucleotides) </Li> <Li> 5 S rRNA (120 nucleotides) </Li> <Li> 5.8 S rRNA (154 nucleotides) </Li> </Ul> </Td> <Td> <Ul> <Li> 23S rRNA (2839 nucleotides) </Li> <Li> 5S rRNA (122 nucleotides) </Li> </Ul> </Td> </Tr> <Tr> <Th> Small subunit </Th> <Td> Sedimentation coefficient </Td> <Td> 40 S </Td> <Td> 30 S </Td> </Tr> <Tr> <Td> Molecular mass </Td> <Td> ~ 1.2 × 10 Da </Td> <Td> ~ 0.7 × 10 Da </Td> </Tr> <Tr> <Td> Proteins </Td> <Td> 32 </Td> <Td> 20 </Td> </Tr> <Tr> <Td> rRNAs </Td> <Td> <Ul> <Li> 18S rRNA (1753 nucleotides) </Li> </Ul> </Td> <Td> <Ul> <Li> 16S rRNA (1504 nucleotides) </Li> </Ul> </Td> </Tr> </Table>

Which of the following rrna types do you need to make up a eukaryotic ribosome