Proteins and Enzymes

ID #1026

I know that proteins are put together by condensation reactions, however, I am confused about the N --> C direction complex. When an N terminus and C terminus are combined, which way are more added on? I heard in class that you only add the incoming amino to carboxyl-terminus. So would the addition be: C<--N-C


I understand your confusion, and you are correct in your description of the addition of the "next" amino acid. The frame of reference we use when describing the directionality of protein synthesis is from the perspective of a growing protein. As we'll see in more detail soon enough, a ribosome always adds the incoming amino acid to the C terminus of the existing protein. So a ribosome never adds a new amino acid to the N-terminus of the protein, and therefore we can say the protein is growing only at its C-terminus. That's why we say protein synthesis occurs from the N-terminus to the C-terminus, or the N --> C direction.

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