This paper describes the significance and process of RNA transcriptional processing and modification

Hungry. Transcription of RNA is fine as long as it conforms to the central law.

1. Form a 5'-end hat structure;(Eukaryotes.)

The 5'-end of the mRNA precursor and the vast majority of mature mRNAs contain 7-methylguanosine as the end of the cap structure, which is made up of GTP and the 5'-end of the precursor mRNA triphosphate nucleotide.

The product of the condensation reaction. ）

2. The formation of 3'-end polynucleotides, that is, polya sequences, the general length of polya sequences varies depending on the type of mRNA, generally 40 200 nt

3. In addition to the addition of emulation and tailing, some mRNAs also have a small amount of nucleotides that are modified. Such as certain adenines.

C6 is methylated.

4. Gene splicing. That is, the introns are cut off and the exons are spliced.

Excerpted from).

Generally this question is for eukaryotes.

One. mrna

1) Beginning and end grooming.

The 5' end is modified with the M7GPPPN cap structure, which is completed within the nuclear stupidity.

The 3' end is modified with the addition of a polyaa tail and is completed in the nucleus.

2) Splicing of mRNA.

Introns are removed from the initial transcript transcribed from the DNA template strand.

And exons.

The process of joining together to form a continuous RNA molecule.

3）mrna。

RNA refers to altering genetic information at the mRNA level.

process. Specifically, it refers to the mRNA molecule produced by gene transcription.

due to nucleotides.

The deletion, insertion or substitution of the gene does not complement the coding sequence of the gene, so that the amino acid composition of the protein prepared by the translation is different from the coding information in the gene sequence.

Two. trna

1) The 5' end leader sequence is excised by RNasep.

2) The 3' end is made by the addition of CCA-OH by the tRNA nucleotidyl transferase as the end.

3) It also includes rare base generation, methylation, etc.

Three. rrna

1) Inside the nucleus of eukaryotes are the transcription products of 45s, which are the predecessors of the three RNAs.

2) Formation of small subunit 18s-RNA

3) Formation of large subunit 28s, rrna

Depending on the situation, the focus is on post-mRNA processing modifications. I don't know if that's what you're asking.

The transcription process of RNA can be divided into three stages, namely: initiation, extension, and termination.

1. Start. RNA polymerase.

Correctly identify the promoter on the DNA template strand.

A ternary initiation complex of enzymes, DNA, and nucleoside triphosphates (NTPs) is formed, from which transcription begins.

2. Extension. Subunit.

Detached from the enzyme molecule, the core enzyme is left with loose binding to the DNA, making it easier to move forward. Core enzymes have no template specificity and can transcribe any sequence on the template, including intermediaries to be excised during post-transcriptional processing.

Order. Subunits that are detached from the core enzyme can also bind to other core enzymes and participate in another transcription process.

3. Termination. Termination of transcription involves the cessation of elongation and release of RNA polymerase and synthesized RNA. in prokaryotes.

Genes or operons.

There is usually a termination sequence at the end of the terminator, the terminator; This is where RNA synthesis ends. Prokaryotic cells.

Transcriptional termination requires the help of a terminating factor (a protein made up of six subunits). (Eukaryotes.)

There may also be a signal of transcriptional termination on the DNA.

1. Transcription complex recognition and binding in the promoter region; Start 2: RNA polymerase catalyzes the addition of ribonucleotides to form mRNA; Extension 3, transcription cessation at the terminator site; Pull the plug.

4. Eukaryotes involve 5' capping and 3' tailing, as well as the splicing of introns.

RNA transcription is divided into four stages:

1.Identification of templates.

RNA polymerase recognizes and binds to the promoter under subunit guidance, and then the DNA duplex is locally unwound, forming a region called a transcription bubble. Melting occurs only at the site where it binds to RNA polymerase.

2.Initiation of transcription.

At the beginning of transcription, the enzyme continues to bind to the promoter, first synthesizing the RNA strand with the first 2 9 nucleotides. The subunit then detaches from the core enzyme, which leaves the promoter, and the initiation phase ends.

3.Extension of transcription.

In the elongation stage, as the enzyme moves forward along the DNA molecule, the thawing region also moves, and the nascent RNA strand grows continuously, and forms an RNA-DNA hybrid with the DNA template strand in the thawing region, after which the DNA restores the double helix structure and the RNA strand is replaced.

4.Termination of transcription.

Finally, RNA polymerase, with the help of the NUSA factor (subunit), recognizes the transcriptional termination signal, stops the growth of the RNA strand, the enzyme and RNA strand leave the template, and the DNA restores the double helix structure.

The meaning is many:

1. The transcribed RNA cannot be used directly to translate proteins, and introns (eukaryotic animals) must be removed to translate the correct proteins.

2. RNA is transcribed in the nucleus, but it needs to be translated into protein in the cytoplasm, and the processed RNA can enter the cytoplasm and will not be explained by the enzymes in the cytoplasm (RNA is a very unstable biological macromolecule, because RNA enzymes are widely available, both in vivo and in vitro).

3. Part of RNA must have a secondary structure, and post-transcription processing can make RNA form a correct secondary structure.

4. After the RNA is processed, it will be added with a cap and tail structure, which are actually the "tags" of ribosome recognition, which is easier to identify and translate. ,8,

2. Eukaryotes.

Ribosomal RNA: The number of copies of genes is high, ranging from tens to thousands. The genes are arranged in clusters and transcribed by RNA polymerase I to produce a longer precursor, which is 45 seconds in mammals.

The nucleolus is the site of RNA synthesis and ribosomal subunit biosynthesis. Endonucleases such as RNA enzyme III play an important role in processing. The 5SRNA genes are also arranged in clusters, transcribed by RNA polymerase III, and are processed to form large subunits.

Ribosomal RNA can be methylated, mainly in the nucleoside 2' hydroxyl group, which is more methylated than prokaryotes. Most ribosomal RNAs do not have introns, and some have introns but are not transcribed.

Second-transporter RNA: transcribed by RNA polymerase III, the processing is similar to that of the prokaryotes, but the CCA at the 3' end is added later, and there is also a 2'-O-methylribose.

Tri-messenger RNA: The genes of eukaryotes encoding proteins have a single gene as the unit of transcription, but have introns that need to be removed. The original transcription product of messenger RNA is a precursor with a large molecular weight, and when processed within the nucleus, it forms an intermediate of varying size, called intranuclear heterogeneous RNA (hnRNA).

The processing process includes:

1 5' end plus cap: formed early in transcription or before transcription termination. First, a phosphoric acid is removed from the 5' end, and then a 5',5' triphosphate bond is formed with GTP, and finally methylated with S-adenosylmethionine to form a cap structure.

There are many types of hat structures, which play a role in identification and stabilization.

2 3' end plus tail: done within the nucleus. It is first cut at the 3' end by RNase III and then tailed by polyadenylic acid polymerase. The tail is associated with passage through the nuclear envelope and also prevents degradation by exonucleases.

3 Internal methylation: mainly 6-methyladenine, which is already present in HNRNA. May play a role in the recognition of the processing of precursors.

3. RNA splicing.

A splicing of transport RNA: Catalyzed by enzymes, enzymes recognize common secondary structures rather than sequences. Usually the intron is inserted close to the anticodon and pairs with the anticodon, replacing the anticodon ring.

The first step is to excise the insertion sequence by the endonuclease, without ATP; The second step is ligated by RNA ligase, which requires ATP.

Splicing of ribosomal RNA of Tetrahymena: Some Tetrahymena 26S ribosomal RNA genes have an intron that can be spliced in the presence of monovalent and divalent cations and guanylate or guanosine. Its essence is the transfer reaction of phosphate esters, and guanylate acts as a cofactor, providing a free 3' hydroxyl group.

Tri-messenger RNA: The introns of the nuclear genes of eukaryotes encoding proteins belong to the second category of introns, with GT at the left end and AG at the right end. The left end is cut first, and the resulting 5' end forms a 5',2'-phosphodiester bond upstream of the 3' end, forming a lasso structure.

The right end of the intron is then cut and the two exons are connected. Different messenger RNAs can be formed through different splicing methods.

Answer]: The mRNA of eukaryotes is in 5'and 3'Both ends are to be modified, and the tassel is modified with the addition of "hat" and "tail"; The shearing of eukaryotic mRNA precursors includes the shearing of introns and the splicing of the remaining fragments into mature mRNA. All rRNA transcripts in eukaryotes need to be processed in a process similar to that of prokaryotes, i.e., splicing'Terminal and excision of unwanted annihilation regions in transcripts.

The tRNA of the eukaryotic sibling is also a large transcript (a precursor transcript of the tRNA) that may contain the order of one or more tRNAs. Mature tRNA is also cleaved after transcription.