The ribosome cycle during protein synthesis process

The process of protein synthesis.

To put it simply, it is to change the order of bases in an mRNA molecule to the order of amino acids in a protein or polypeptide chain.

Specifically: Initiation stage: After the mRNA is synthesized in the nucleus, it enters the cytoplasmic matrix through the nuclear pore, binds to the ribosome, carries the tRNA of methionine, and enters site 1 through complementary pairing with the base AUG.

Carrying: According to the codon guidance on site 2, the tRNA of the corresponding amino acid enters site 2, which is called carrying.

Shift: The ribosome moves back the position of three bases, the original site 2 becomes site 1, and the new site 2 is vacant, continue to carry out the carry transpeptide and shift, not only repeat these three steps, each cycle, there is one more amino acid on the polypeptide chain, and the polypeptide chain is extended a little.

Until the codon at site 2 is UAA, UAG, or UGA, the polypeptide chain is extended to this point because there is no corresponding tRNA and amino acid binding to the stop codon.

The generalized nucleoprosomal cycle refers to the process of condensation on the nucleoprotein body to form a polypeptide chain after the activation of amino acids, which includes the initiation of peptide chain synthesis, the extension of peptide chain, the termination and release of peptide chain synthesis, and the narrow nucleoproteome cycle refers to the peptide chain extension stage in the process of polypeptide chain synthesis, which is carried out by three steps of carrying, peptide formation and translocation until the termination stage.

The three stages of the protein synthesis process are as follows:1. The initiation of peptide chain synthesis: firstly, IF1 and IF3 are combined with the 30S subunit to prevent the binding of the large subunit; Subsequently, IF2 and GTP bind to the small subunit to facilitate subsequent binding of the initiating tRNA; The formed small subunit complex is attached to the mRNA through ribosomal binding sites, and the initiation tRNA pairs with the AUG initiation codon and releases IF3, and a 30S initiation complex is formed.

2. Extension of peptide chain: first, the complex formed by loaded tRNA with EF-TU and GTP is transported to the ribosome, GTP is hydrolyzed, EF-TUDGDP is released, and under the action of EF-TS and GTP, EF-TUDGDP can be reused; The peptidyl transferase then attaches the two adjacent amino acids; Finally, the shift releases the unloaded tRNA and transports the nascent peptide strand to the p-site.

3. Peptide chain termination and release: The release factor recognizes the stop codon and promotes the peptidyl transferase allosterism under the action of RP3. The ester bond between the polypeptide chain and the tRNA carried by the tRNA is hydrolyzed and severed, the polypeptide chain is released from the nucleosome and tRNA, and finally the proteosome is separated from the mRNA.

Synthesized on sessile ribosomes;

The structure of ribosomes is significantly different from that of other organelles: they are not membrane-coated, they are composed of two subunits, and they can attach to the endoplasmic reticulum or be free of the cytoplasm because of their functional needs. Thus, ribosomes are also considered intracellular macromolecules rather than a class of organelles.

The central law states that the process of translating RNA into proteins occurs in ribosomes. During translation, the small subunit of the ribosomal first binds to the messenger RNA transcribed from the nucleus, reads the mRNA information, and then combines with the large subunit of the ribosomal to form a complete ribosome, which synthesizes the amino acid molecules transported by the transport RNA into polypeptides. When the ribosome completes the translation of a single strand of mRNA, the large and small subunits are separated again.

Free ribosomes.

Free ribosomes can move anywhere in the cytoplasm but are excluded from the nucleus and other organelles. Proteins produced by free ribosomes are released into the cytoplasm and used within the cell. Since the cytoplasm contains a high concentration of glutathione, it is a reducing environment, therefore, the free ribosomes in the cytoplasm cannot produce proteins containing disulfide bonds formed from oxidized cysteine residues.

Membrane-bound ribosomes.

When ribosomes start synthesizing proteins that are required for certain organelles, ribosomes can bind to membranes. In eukaryotic cells, this binding occurs on the rough endoplasmic reticulum (ER). Ribosomes insert newly generated polypeptide chains directly into the ER, which are then transported to their destination via the secretory pathway.

Proteins produced by membrane-bound ribosomes are usually used within the plasma membrane or excreted from the cell by exocytosis.

Ribose deficiency body protein is not only involved in protein biosynthesis. () Oak Honor.

a.That's right. b.Mistake.

Correct Answer:

Answer]: The nucleoprotein body circulation is divided into three stages: initiation, peptide chain lengthening and termination.

During starting, a start-up complex is formed. mRNA binds to small subunits and is assisted by IF1 and IF-3; At the same time, fmet-tRNA recognizes and binds to the start codon AUG of mRNA, where IF-3 is shed, and IF-2 and GTP participate in the reaction. The large subunit of 50s binds to the small subunit, and the initiating factors IF-1 and IF-2 are shed. The first methionine carried by the fmet-tRNA is located at the nucleosome of the donor site.

In the peptide chain elongation phase, each additional amino acid is repeated in four steps: carrying, transpeptidization, shedding, and displacement. A brief description of each step is given.

In the termination phase, the factor RF is terminated, and RF causes the donor transpeptidase to become hydrolyzed, and the synthesized peptide chain is hydrolyzed and released from the nucleosome. Protein synthesis is an energy-required reaction, and for each peptide bond generated, a total of 4 high-energy phosphate bonds need to be consumed. The nucleoprotein body detached from the mRNA is broken down into two subunits, large and small, and factor 3 (1f-3) is required for the depolymerization process of the nucleoproteosome.

Nucleosomes can then participate in new synthesis processes.