So I understand that tRNA bonds to a codon (with an anticodon) in the translation process. I read in my biology textbook that the ribosomes "read" the mRNA strand.

Why do the ribosomes need to read the mRNA strand? Are the ribosomes able to intepret the message and bring the correct anticodon to it? Or is the main function of the ribosomes just to join amino acids to make polypeptides? I'm just confused why the ribosomes read the mRNA strand when it seems like there is no need to.

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    $\begingroup$ Welcome to SE Biology. As your question appears to be just a misunderstanding of rather loose language I am giving a brief response in a comment and pointing you to an online source where you can find more detail. Yes, it is the anticodon of the tRNA that decodes the codons in the mRNA, so strictly speaking it is the tRNA that reads the mRNA (no need for the word "strand"). However the ribosome is required for this complex process, and it is where the tRNA, mRNA and other components bind, so the author is expressing this idea loosely $\endgroup$ – David Dec 4 '18 at 9:55
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    $\begingroup$ Since ribosomes act as a catalyst I would assume the reaction could happen without them but is would be many orders of magnitude slower, and likely to produce erroneous results of fail halfway. Its not a bad question but it could be worded clearer. "can it occur without ribosomes" would be a good foundation question. $\endgroup$ – John Dec 4 '18 at 16:35
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    $\begingroup$ @John — Protein synthesis is not a single reaction. Whereas peptide bond formation could occur at a slow rate without ribosomes, the other requirement to hydrogen bond to the mRNA at the same time makes that kinetically very difficult, and then you have to start at a particular place on the mRNA and continue. Yes it must have evolved from a simpler system, but no, it's very different from a simple catalyst. And don't encourage people to ask "could" questions — they generally yield subjective answers — we need "can" questions that are answerable. $\endgroup$ – David Dec 4 '18 at 23:01
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    $\begingroup$ @David Hence my statement that the question could be reworded as can the reaction occur without ribosomes. Which should be established before the above questions. Also I never implied ribosomes were not important, just that exploring how the system could function without them would be a better way to answer the OP's unfocused questions. For instance one thing we know for instance is that many mismatches in mRNA codon binding is because the RNA molecules are not rigid and can distort to form a wider range of binding, one function of ribosomes may be to limit such distortion. $\endgroup$ – John Dec 5 '18 at 5:43
  • $\begingroup$ @John — OK. But I think the poster can answer his question by reading a better account of ribosomal protein synthesis. I neglected to mention that your question is answered in a way by non-ribosomal synthesis of cyclic peptides by certain bacteria. Any new question would need checking that it hadn't been covered previously. $\endgroup$ – David Dec 5 '18 at 8:30

The first two sentences of the Wikipedia Ribosome article say:

The ribosome... serves as the site of biological protein synthesis (translation). Ribosomes link amino acids together in the order specified by messenger RNA (mRNA) molecules.

Slightly later, in the Overview section it says:

Ribosomes can bind to a messenger RNA chain and use its sequence for determining the correct sequence of amino acids for generating a given protein. Amino acids are selected, collected, and carried to the ribosome by transfer RNA (tRNA) molecules, which enter one part of the ribosome and bind to the messenger RNA chain. It is during this binding that the correct translation of nucleic acid sequence to amino acid sequence occurs.

And it then tells us "The attached amino acids are then linked together by another part of the ribosome."

So, the function of the ribosome is to make sure each codon of the mRNA is matched up with the correct tRNA, and then to catalyze the linkage of the associated amino acid to the growing chain of the protein being built.


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