Editing Ribosome (section)

==Overview==
The sequence of [[DNA]] that encodes the sequence of the [[amino acids]] in a protein is transcribed into a [[messenger RNA]] (mRNA) chain. Ribosomes bind to the messenger RNA molecules and use the RNA's sequence of [[nucleotide|nucleotides]] to determine the sequence of amino acids needed to generate a protein. Amino acids are selected and carried to the ribosome by [[transfer RNA]] (tRNA) molecules, which enter the ribosome and bind to the messenger RNA chain via an [[anticodon]] stem loop. For each coding triplet ([[codon]]) in the messenger RNA, there is a unique transfer RNA that must have the exact anti-codon match, and carries the correct amino acid for incorporating into a growing [[polypeptide]] chain. Once the protein is produced, it can then [[protein folding|fold]] to produce a functional three-dimensional structure.

A ribosome is made from [[biomolecular complex|complexes]] of RNAs and proteins and is therefore a [[Ribonucleoprotein particle|ribonucleoprotein complex]]. In prokaryotes each ribosome is composed of small (30[[Svedberg|S]]) and large (50[[Svedberg|S]]) components, called subunits, which are bound to each other:

# (30S) has mainly a decoding function and is also bound to the mRNA 
# (50S) has mainly a catalytic function and is also bound to the aminoacylated tRNAs.

The synthesis of proteins from their building blocks takes place in four phases: initiation, elongation, termination, and recycling. The start codon in all mRNA molecules has the sequence AUG. The stop codon is one of UAA, UAG, or UGA; since there are no tRNA molecules that recognize these codons, the ribosome recognizes that translation is complete.<ref>{{cite web|url=https://nature.com/scitable/definition/translation-rna-translation-173|title=Scitable by nature translation / RNA translation}}</ref> When a ribosome finishes reading an mRNA molecule, the two subunits separate and are usually broken up but can be reused. Ribosomes are a kind of [[enzyme]], called [[ribozyme]]s because the [[Catalysis|catalytic]] [[peptidyl transferase]] activity that links amino acids together is performed by the ribosomal RNA.<ref name="Tirumalai-2021a">{{cite journal | vauthors = Tirumalai MR, Rivas M, Tran Q, Fox GE | title = The Peptidyl Transferase Center: a Window to the Past | journal = Microbiol Mol Biol Rev | volume = 85 | issue = 4 | pages = e0010421 | date = November 2021 | pmid = 34756086 | pmc = 8579967 | doi = 10.1128/MMBR.00104-21}}</ref>

In [[eukaryote|eukaryotic cells]], ribosomes are often associated with the intracellular membranes that make up the [[endoplasmic reticulum#Rough endoplasmic reticulum|rough endoplasmic reticulum]].

Ribosomes from [[bacteria]], [[archaea]], and [[eukaryote]]s (in the [[three-domain system]]) resemble each other to a remarkable degree, evidence of a common origin. They differ in their size, sequence, structure, and the ratio of protein to RNA. The differences in structure allow some [[antibiotic]]s to kill bacteria by inhibiting their ribosomes while leaving human ribosomes unaffected. In all species, more than one ribosome may move along a single mRNA chain at one time (as a [[polysome]]), each "reading" a specific sequence and producing a corresponding protein molecule.

The [[mitochondrial ribosome]]s of eukaryotic cells are distinct from their other ribosomes. They functionally resemble those in bacteria, reflecting the evolutionary origin of mitochondria as [[endosymbiotic]] bacteria.<ref>{{cite journal | vauthors = Benne R, Sloof P | title = Evolution of the mitochondrial protein synthetic machinery | journal = Bio Systems | volume = 21 | issue = 1 | pages = 51–68 | year = 1987 | pmid = 2446672 | doi = 10.1016/0303-2647(87)90006-2 | bibcode = 1987BiSys..21...51B }}</ref><ref>{{cite web|url=http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Ribosomes/Ribosome.HTML|title=Ribosomes|access-date=2011-04-28|url-status=dead|archive-url=https://web.archive.org/web/20090320163538/http://www.cs.stedwards.edu/chem/Chemistry/CHEM43/CHEM43/Ribosomes/Ribosome.HTML|archive-date=2009-03-20}}</ref>