Amino acids are the building blocks of proteins and have a common structure consisting of a central carbon atom (the alpha carbon) to which four groups are attached:
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Amino group (-NH2): This functional group is the same for all amino acids and contains a nitrogen atom bonded to two hydrogen atoms.
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Carboxyl group (-COOH): This group is also found in all amino acids and contains a carbon atom doubly bonded to an oxygen atom and singly bonded to a hydroxyl group (-OH).
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Hydrogen atom (H): This is a single hydrogen atom attached to the central carbon.
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R group or side chain (variable group): This is the group that differentiates one amino acid from another. The R group can vary in size, shape, charge, hydrophobicity, and reactivity. There are 20 standard amino acids, and the differences in their R groups lead to the diverse properties of amino acids.
The diversity of the R groups allows amino acids to exhibit a wide range of chemical behaviors, influencing protein structure, stability, and function. Based on the characteristics of the R groups, amino acids can be classified into categories such as nonpolar, polar, charged (acidic or basic), and aromatic, which also affects how they interact with each other and with other molecules.