ID #2030

I was hoping you could explain why the correct answer is what it is for the following question:Q- During translation termination: A-Correct: a release factor recognizes and binds a stop codon at the A site. I have a feeling I am not reading this the right way, but to me this answer is saying that the release factor physically binds a stop codon at the A-site, rather than the codon just being the nucleotide triplet in the mRNA sequence which the release factor recognizes, and then "sits" in the A site.

One of the difficulties in truly learning to think about biology is getting past the 2-dimensional nature of drawings and "letters." In biology, everything has a three dimensional shape, and there are always consequences and significance to that shape. When we talk about a protein interacting with a nucleic acid, for example, just what does that really mean? It means the tertiary structure of the protein is folded such that a 3-D shape has been formed which "fits" with some other object. You can't put a baseball glove on your foot, because it doesn't fit, right? But you put it on your hand, and it just slips right in. In this case, the shape of the protein "fits" with the shape of the nucleic acid in that particular spot. Don't think of adenine or cytosine as A or C, think of them as three dimensional molecules with a unique landscape. Put a uracil next to a guanine, and you've got a different shape. Put a uracil next to a guanine next to an adenine, and the shape is different yet again. And mabye the shape we created in our last example is a landscape that fits the tertiary structure of a region of a release factor. We see UGA and think "stop codon," but a release factor sees a uracil next to a guanine next to an adenine and "sees" something it can bind to because they fit together.

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