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ribosome

Granular organelle

synonym Riboribosome Ribosome

ribosome Ribosome, formerly known as "ribosome" or "ribosome", is generally considered to be a kind of cell Organelle , except mammal ripe red blood cell , plants sieve tubes In addition, ribosomes exist in all cells. In general, Prokaryotic cell There is only one ribosome, and Eukaryotic cell There are two ribosomes (including mitochondrion Ribosomes in cytoplasm Ribosomes are different).

The ribosome structure and other organelles are significant difference : No membrane coating, composed of two Subunit Components can be attached to Endoplasmic reticulum Or dissociate from cytoplasm 。 Therefore, ribosomes are also considered as intracellular macromolecule It is not a kind of organelle.

“ Central rule ”Inside RNA The process of translating to protein occurs in the ribosome. When translating, Ribosome small subunit First and second nucleus Transcribed in Messenger RNA Combining, reading mRNA Information, Recombine Ribosome large subunit , forming a complete ribosome Transport RNA Delivered amino acid molecule Synthetic polypeptide 。 When the ribosome completes the After translation , large and small subunits will be separated again.

Chinese name: ribosome
Foreign name: Ribosome
Discipline: biology
Alias: Riboribosome

Discovery time: 1953
Discoverer: Ribinson and Broun
Composition: By RNA (rRNA) and protein
Abbreviations: RI

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definition

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Ribosome morphology^[1]

Ribosomes are intracellular Ribonucleoprotein granule (ribbon protein particle), mainly composed of RNA （ rRNA ）And protein, whose function is to Genetic code convert to amino acid Sequence and construction from amino acid monomer protein polymer 。 Ribosomes are also called intracellular protein synthesis Of Molecular machine 。

ribosome^[2]

form

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Ribosome structure^[3]

Ribosome is a highly complex cellular machine. It is mainly composed of Ribosomal RNA (rRNA) and dozens of different Ribosomal protein （r- protein ）Composition (the exact number of species varies slightly). Ribosomal protein And rRNA are arranged into two different sizes Ribosomal subunit , commonly referred to as the size subunit of ribosome. Ribosome large and small subunits cooperate with each other in protein synthesis Transforming mRNA into Polypeptide chain 。

prokaryote The diameter of ribosome is about 20 nm, which is composed of 65% rRNA and 35% ribosomal protein^[4] 。 Eukaryote The diameter of ribosomes is between 25 and 30 nm, and the ratio of rRNA to protein is close to 1^[5] 。 The ribosomal subunits of bacteria and eukaryotes are very similar^[6] 。

Ribosome under electron microscope^[7]

Used to describe ribosomes Subunit And rRNA fragments Unit of measurement It is a Svedberg unit, representing the sedimentation rate of subunit during centrifugation rather than its size. For example, bacteria 70S ribosome It is composed of 50S and 30S subunits.

function

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Translation of mRNA

The main function of ribosome is to convert genetic code into amino acid sequence and construct protein polymer from amino acid monomer. MRNA contains a series of Codon , decoded by ribosomes to produce proteins. The ribosome uses mRNA as a template. The ribosome passes through each codon (3 nucleotide ）, combine it with aminoacyl group- tRNA Appropriate amino acid pairing provided. Aminoacyl tRNA has codon complementary Anticodon The other end carries appropriate amino acids. Ribosomes use large conformational changes to quickly and accurately identify appropriate tRNAs^[8] 。 It is usually associated with the first amino acid methionine Aminoacyl tRNA binding Ribosome small subunit Combine with AUG codon and recruit Ribosome large subunit 。 The ribosome contains three RNAs binding site : A, P and E site 。 Site A Binding of aminoacyl tRNA or termination Release factor^[9] ； P-site binding Peptide group -TRNA (tRNA binding to tRNA) Polypeptide chain ； The E site (exit) binds free tRNA. Protein synthesis begins near the end of mRNA5 ' Initial codon AUG P site combination. Ribosome by using prokaryote The Shine Dalgarno sequence of mRNA in and the Kozak box in eukaryotes identify the starting codon.

Translation co folding

Ribose volume polar participation protein folding^[10] 。 In some cases, ribosomes are essential for obtaining functional proteins. For example, folding of deeply knotted proteins depends on the ribosome pushing the chain through the attached ring^[11] 。

Add translation independent amino acids

The existence of ribosome quality control protein Rqc2 is related to the extension of mRNA independent protein polypeptide chain^[12] 。 This extension is the result of ribosome adding CAT tail through tRNA brought by Rqc2.

Peptide transfer and peptide hydrolysis

Ribosomes in Peptide group Transfer and peptide hydrolysis are two extremely important biological processes Catalysis^[13] 。

classification

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bacterial ribosome

Ribosome of bacteria 70S ribosome By 30S Small subunit And 50S Large subunit form. 30S small subunit contains 16S RNA (1540 nucleotides) and 21 kinds Ribosomal protein ； The large subunit consists of 5S RNA (120 nucleotides), 23S RNA (2900 nucleotides) and 31 ribosomal proteins^[6] 。

Eukaryotic ribosome

The eukaryotic ribosome 80S ribosome is located in its Cytoplasm 。 Each ribosome consists of 40S small subunit and 60S large subunit. 40S subunit has 18S RNA (1900 nucleotides) and 33 proteins^[14-15] 。 The 60S large subunit consists of 5S RNA (120 nucleotides), 28S RNA (4700 nucleotides), 5.8S RNA (160 nucleotides) and 46 ribosomal proteins^[6]^[14-15] 。

Mitochondrial ribosomes and plastid ribosomes

Eukaryotes, located in mitochondrion The ribosome in is called Mitochondrial ribosome (mitoribosomes), located at Plastid The ribosomes of chloroplast In Chloroplast ribosome （chloroplastic ribosomes）。 They are also 70S ribosomes combined by large and small subunits and proteins, similar to bacteria^[6] 。 In both, chloroplast ribosomes are closer to bacteria than mitochondrial ribosomes. Many of the mitochondria Ribosomal RNA Is shortened, and its 5S rRNA is replaced by other structures in animals and fungi^[16] 。

Pharmaceutical chemists use the difference between bacteria and eukaryotic ribosomes to produce antibiotics such as Aminoglycoside antibiotics 、 Tetracycline antibiotics etc. Protein synthesis inhibitor Antibiotics like, Specificity To destroy bacterial infection. Because of their different structures, bacterial 70S ribosomes are vulnerable to these antibiotics, while eukaryotic 80S ribosomes are not^[17] 。 Although mitochondria have ribosomes similar to bacteria, they are not affected by these antibiotics, because they are surrounded by double membranes and are not easy to bring these antibiotics into Organelle^[18] 。 The same is true of chloroplasts^[19] 。

Free ribosome

Free ribosome It can move anywhere in the cytoplasm, but is excluded from nucleus And other organelles. Proteins generated from free ribosomes are released into the cytoplasm and used in cells. Because the cytoplasm contains high concentration of glutathione , it is a kind of Reducibility Therefore, the free ribosomes in the cytoplasm cannot produce Cysteine Residue Formed containing Disulfide bond Protein.

membrane-bound ribosomes

When ribosomes begin to synthesize proteins needed by certain organelles, ribosomes can bind to membranes. stay Eukaryotic cell The combination occurs in rough Endoplasmic reticulum (ER). The ribosome directly inserts the newly generated polypeptide chain into ER, and these polypeptide chains pass through Secretory pathway Is transferred to its destination. membrane-bound ribosomes The protein produced is usually plasma membrane Internal use, or through Exocytosis Excretion from cells^[20] 。

structure

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Although ribosomes vary greatly in size, their core structures are very similar. Most rRNAs are highly organized into various Tertiary structure Motif 。 Additional RNAs in larger ribosomes appear in the form of several long consecutive insertions, making them form rings in the core structure without being damaged or changed^[6] 。 All of the ribosomes catalytic activity All are carried out by RNA, and the protein on its surface can stabilize the rRNA structure^[6] 。

ultrastructural

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The average ribosome in the early 1970s molecular structure Gets parsed. At the beginning of the 21st century, the ribosome structure has achieved high resolution resolution, reaching an accuracy of about several nm.

In 2000, the paleontology Haloarcula marismortui^[21] And bacteria Deinococcus radiodurans^[22] 50S subunit and Thermophilus^[23] The atomic resolution ribosome structure of the 30S subunit was analyzed almost simultaneously. These studies were obtained in 2009 Nobel Prize in Chemistry 。

2005 Escherichia coli 70S ribosome based on X-ray crystal Empty ribosome structure with a resolution of 3.5 ∨^[24] , based on freezing electron microscope With a resolution of 11-15 ∨ Neosynthesis The ribosome structure is analyzed when the protein chain of^[25] 。

In 2006, the resolution was 2.8 ∨ and 3.7 ∨ tRNA and MRNA molecule Compound Ribose body atomic structure It is analyzed by X-ray crystal. These structures enable people to see the details of the interaction between the Thermophilus ribosome and mRNA and the tRNA binding to the classical ribosome site. Subsequently, the structure of the interaction between ribosome and long mRNA containing Shine Dalgarno sequence with a resolution of 4.5-5.5 ∨ was also analyzed^[26] 。

In 2011, from Saccharomyces cerevisiae (Saccharomyces cerevisiae) Crystallography get^[27] 。 This model reveals that eukaryotes Specificity The structure of the element and its relationship with the generally conservative core Interaction 。 Same year, thermophilic Tetrahymena (Tetrahymena thermophila) eukaryotic 40S^[15] And 60S^[28] The complete model of ribosome structure is analyzed. The structure of 40S subunit describes the structure of 40S subunit and the Translation Start Interaction with eIF1 in the process^[15] 。

biosynthesis

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Bacterial cells pass through multiple ribosomes Gene operon Transcription of cytoplasm Ribosomes are synthesized in the. stay Eukaryote The synthesis process occurs in the cytoplasm and nucleolus The assembly process involves four kinds of rRNA synthesis, processing and assembly Coordination role More than 200 kinds of proteins.

Origin of ribosome

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Ribosomes may have originated from RNA , looks like a Self replication The complex of amino acid Only after its appearance did it evolve to have Synthetic protein Ability. Transforming ribosome from an ancient self replicating machine to its current form of translation machine drive It may be that proteins are bound to the self replication mechanism of ribosomes Select pressure This change increases its ability to self replicate^[29] 。

Differentiated ribosome

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It is generally believed that the ribosome Prokaryote and Eukaryote There are two kinds of ribosomes. But ribosomes Heterogeneity Surprisingly, ribosomes have different compositions in different species. And main Model organism Compared with typical ribosomes in, heteroribosomes have different structures and therefore have different activities.

Heterogeneity of ribosome composition is involved in protein synthesis Translation control^[30] 。 Different Cell population Specific ribosomes can affect the way genes are translated^[31] 。 some Ribosomal protein Exchangeable with cytoplasmic replicates from the assembled complex^[32] It shows that the structure of ribosomes in vivo can be modified without synthesizing new ribosomes.

Ribosomal protein

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A group of highly acidic ribosomal proteins (RP), also known as P proteins, exist in 60S as multiple copies in the ribosomal stem Subunit P protein mediates selective translation^[33] 。 These P proteins can be found in yeast and Mammalian cell Found in. If there is no P protein in yeast, yeast is sensitive to cold. If Human cells Loss of P protein, induction Autophagy^[34] 。

Some ribosomal proteins are absolutely critical, while others Nucleoprotein Is not. For example, in mice, Rpl38 is necessary for the translation of Hox mRNA subgroups, and the mutation of Rpl38 results in Short tail Homology of Heteromorphic transformation^[35] 。

The modification of core ribosomal protein (RP) can also lead to the formation of heterogeneous ribosomes.

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