MRNA
Also known as messenger RNA. The function of mRNA is to accurately transcribe genetic information from DNA, and then determine the amino acid sequence of proteins based on the base sequence of mRNA, completing the process of genetic information transmission in the gene table. In Eukaryote, the precursor RNA of transcription contains a large number of non coding sequences, and only about 25% of the sequences are processed into mRNA and finally translated into proteins. Because this unprocessed precursor mRNA (pre mRNA) varies greatly in molecular size, it is commonly referred to as heterogeneous nuclear RNA (hnRNA).

TRNA
Also known as transport RNA. If mRNA is the blueprint for protein synthesis, Ribosome is the factory for protein synthesis. However, the raw materials for synthesizing proteins -20 amino acids - lack special affinity with the bases of mRNA. Therefore, it is necessary to use a special RNA transfer RNA (tRNA) to transport amino acids to Ribosome, and tRNA can accurately link the amino acids it carries to form polypeptide chains according to the Genetic code of mRNA. Each amino acid can bind to 1-4 tRNAs, with over 40 known types of tRNAs. TRNA is the smallest RNA with an average molecular weight of approximately 27000 (25000 30000) and consists of 70 to 90 nucleotides. Moreover, it has the characteristics of rare bases. In addition to Pseudouridine and Hypoxanthine nucleosides, rare bases are mainly methylated purine and pyrimidine. This type of rare base is usually formed by special modifications after transcription.

RRNA
Also known as Ribosome RNA (rRNA), rRNA is the main component of Ribosome. Ribosome is the factory for protein synthesis. In Escherichia coli, rRNA accounts for 75% -85% of the total cell RNA, while tRNA accounts for 15% and mRNA only accounts for 3-5%.
Generally, rRNA combines with Ribosomal protein to form Ribosome. If rRNA is removed from Ribosome, the structure of Ribosome will collapse. The Ribosome of Prokaryote contains 5S, 16S and 23S rRNAs.
S is the Sedimentation coefficient. When the sedimentation velocity of a particle is measured by ultracentrifugation, the velocity is proportional to the particle size and diameter. 5S contains 120 nucleotides, 16S contains 1540 nucleotides, and 23S contains 2900 nucleotides. There are four kinds of rRNAs in Eukaryote. Their molecular sizes are 5S, 5.8S, 18S and 28S respectively, and they have about 120, 160, 1900 and 4700 nucleotides respectively. RRNA is a single stranded molecule that contains unequal amounts of A and U, G and C, but has a wide range of double stranded regions. In the double stranded region, alkali genes are connected by hydrogen bonds, exhibiting a hairpin helix.
The function of rRNA in protein synthesis is not yet fully understood. However, there is a segment of nucleotide sequence at the rRNA3 'end of 16S that is complementary to the leading sequence of mRNA, which may contribute to the combination of mRNA and Ribosome.

MiRNA
MicroRNAs (miRNAs) are a class of endogenous non coding RNAs with regulatory function found in Eukaryote, which are about 20-25 nucleotides long. Mature miRNAs are produced by a series of Nuclease shearing processes of longer primary transcripts, and then assembled into RNA induced silencing complexes. They recognize target mRNA by base complementary pairing, and guide the silencing complexes to degrade target mRNA or inhibit target mRNA translation according to the degree of complementarity. Recent studies have shown that miRNAs are involved in various regulatory pathways, including development, viral defense, hematopoietic processes, organ formation, cell proliferation and apoptosis, fat metabolism, and more.

Small molecule RNA
It exists in the nucleus and cytoplasm of Eukaryote, with a length of 100 to 300 bases (the longest of about 1000 bases in yeast). More cells can contain 105~106 such RNA molecules, while less cells can not be detected directly. They are synthesized by RNA polymerase II or RNA polymerase III, and some of them can be capped like mRNA.
There are mainly two types of small molecule RNAs: one is snRNA (small nuclear RNA), which exists in the nucleus; The other type is scRNA (small cytoplasmic RNA), which exists in the cytoplasm.
Small molecule RNA usually forms complexes with proteins and plays an important role in the life activities of cells,.

Antisense RNA
The various RNA molecules mentioned above are transcriptional products, and mRNA is ultimately translated into proteins, while rRNA, tRNA, and snRNA do not carry the information of translation into proteins, and their final product is RNA.

ribozyme
In addition, there is a special type of RNA (its classification is not related to the aforementioned RNA classification) - ribozyme
The term ribozyme is used to describe RNA with catalytic activity, which is essentially ribonucleic acid (RNA) but has the catalytic function of an enzyme. The substrates of ribozymes can be different molecules, some of which are specific parts of the same RNA molecule. Ribozymes have many functions. Some can cut RNA, some can cut DNA, and some also have RNA Ligase, phosphatase and other activities. Compared with protein enzymes, ribozymes have lower catalytic efficiency and are a relatively primitive catalytic enzyme.
Most ribozymes participate in RNA self shearing and processing by catalyzing the hydrolysis of transphosphates and Phosphodiester bond, which also have specificity, even Km value.
The discovery is that after removing the portion of the Escherichia coli RNaseP protein, the RNA portion (MIRNA) left behind has enzymatic activity under high concentrations of magnesium ions in vitro.

Non coding RNA
The new type of dark matter in life is non coding RNA (ribonucleic acid), known as the "dark matter" in living organisms. Recently, Professor Shan Ge's laboratory at the University of Science and Technology of China found a new class of cyclic non coding RNA, and revealed the function and functional mechanism of such non coding RNA. The results were published in the internationally renowned journal Nature Structural and Molecular Biology. Non coding RNA is a large class of RNA molecules that do not encode proteins but play a regulatory role in cells.
Just as there are many invisible "dark matter" and "Dark energy" in the universe, there is also such mysterious "dark matter" - non coding RNA in the "small universe" of life.
More and more evidence suggests that the occurrence and development of a series of major diseases are related to the imbalance of non coding RNA regulation.
Circular RNA molecules have only recently attracted the attention of researchers, while previous research has mainly focused on linear RNA molecules. The new circular non coding RNA discovered in Professor Shan Ge's laboratory is named Exon Intron circular RNA. In the paper, they also studied why these novel circular non coding RNAs became circular rather than linear molecules, and found that complementary repetitive sequences often exist at both ends of the circular sequence.