prokaryote There are three types of rRNAs for RNA: 5SrRNA, 16SrRNA and 23SrRNA. Eukaryote There are four types of rRNAs in the gene expression system: 5SrRNA, 5.8SrRNA, 18SrRNA and 28SrRNA. S is Macromolecular substances A physical unit in ultracentrifugation sedimentation, which can indirectly reflect the size of molecular weight. prokaryote And eukaryotic ribosomes are both large and small Subunit form. 
RRNA structure [2]
Ribosomal RNA Ribosomal RNA has its own characteristics in various organisms, so it can be concluded from the comparison of rRNAs in different organisms that Biological evolution Conclusion of the course. RRNA is Peptidyltransferase (peptidyl transfer) Peptide bond No extra energy is required for formation. In the past, it was believed that proteins with large subunits had enzymatic activity, which promoted the formation of peptide bonds, so they were called transpeptidases. In the early 1990s, H.F. Noller and others proved that Escherichia coli 23SrRNA can catalyze the formation of peptide bonds, which proves that ribosome is a ribozyme Thus fundamentally changing the traditional view. Ribosomes catalyze peptide bond synthesis of rRNA, while proteins only maintain rRNA conformation and play an auxiliary role. RRNA generally Ribosomal protein Combine to form ribosome If the rRNA is removed from the ribosome, the ribosome structure will collapse. prokaryote There are 5S, 16S and 23S rRNAs in the ribosomes of. S is Settlement coefficient (segmentation coefficient), when used Ultracentrifugation When measuring the precipitation speed of a particle, this speed is proportional to the size and diameter of the particle. 5S contains 120 nucleotide 16S contains 1540 nucleotides, and 23S contains 2900 nucleotides. Eukaryotes have four kinds of rRNAs, with molecular sizes of 5S, 5.8S, 18S and 28S, and about 120, 160, 1900 and 4700 nucleotides, respectively. RRNA is a single strand, which contains unequal amounts of A and U, G and C, but has a wide range of Double chain Area. In the double stranded region, alkali gene hydrogen bond Connected, expressed as a hairpin spiral. RRNA in protein synthesis The functions in are not fully understood. However, there is a section at rRNA3 'end of 16S nucleotide sequence MRNA Preamble sequence They are complementary, which may help the combination of mRNA and ribosome. 
Figure 1 Ribosomal RNA It is generally believed that the basic function of ribosome depends on its rRNA, and ribosomal proteins play a role in strengthening the function of rRNA. Ribosomes were originally constructed from rRNA, and some proteins were added to them during evolution. Experiments in vivo and in vitro have proved that ribose lacking certain proteins still exists biological activity ； In addition, rRNA gene (rDNA) mutation and methylation can cause antibiotics (such as erythromycin chloramphenicol ）Resistance. In ribosomes, rRNA is the main structural component, the core of structure and function, and its main functions are:
(1) It has peptidyltransferase activity.
(2) It provides a binding site for tRNA.
(3) It provides binding sites for a variety of protein synthesis factors.
(4) At the beginning of protein synthesis, it participates in selective binding with mRNA and binding with mRNA in the extension of peptide chain.
(5) In addition, the binding of ribosome size subunits, correction reading, correction of nonsense chain or frame drift, and the role of antibiotics are all related to rRNA.
