Protein, asam amino, dan peptida
Proteins consist of chains of 20 different kinds of amino acids connected by covalent linkages called peptide bonds. All amino acids have the same generalized structure as shown in Figure 2-3. An a-carbon is at the center of each amino acid. To its left (as conventionally written) is a basic (when ionized) amino group (NH3 +). To the right of the a-carbon is an acidic (when ionized) carboxyl group (COO−). Ahydrogen atom forms a third bond to the a-carbon, and the fourth bond connects to a side-chain group (R). Amino acids are classified according to the nature of the R group. The 20 different amino acids used in the synthesis of proteins are symbolized by either three letter or single letter abbreviations as listed in Table.
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