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How are protein enzymes built from amino acids?

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A multi-panel diagram illustrates how a substrate binds to an enzyme's active site through induced fit, leading to product formation, and shows how non-substrates and allosteric regulators can alter enzyme activity by binding to different sites on the enzyme. — Enzyme In the induced-fit theory of enzyme-substrate binding, a substrate approaches the surface of an enzyme (step 1 in box A, B, C) and causes a change in the enzyme shape that results in the correct alignment of the catalytic groups (triangles A and B; circles C and D represent substrate-binding groups on the enzyme that are essential for catalytic activity). The catalytic groups react with the substrate to form products (step 2). The products then separate from the enzyme, freeing it to repeat the sequence (step 3). Boxes D and E represent examples of molecules that are too large or too small for proper catalytic alignment. Boxes F and G demonstrate binding of an inhibitor molecule (I and I′) to an allosteric site, thereby preventing interaction of the enzyme with the substrate. Box H illustrates binding of an allosteric activator (X), a nonsubstrate molecule capable of reacting with the enzyme.

Protein enzymes are complex molecules primarily composed of one or more polypeptide chains, which are long sequences of amino acids linked together. The construction of these chains occurs through a highly regulated biological process known as translation.123

The Assembly Process

The synthesis of a protein chain follows these key steps:

Genetic Instruction: The sequence of amino acids is determined by the genetic code, where triplets of bases in messenger RNA (mRNA) specify the order of amino acids to be added.3
Activation and Linking: Amino acids are activated and attached to specific transfer RNA (tRNA) molecules. These tRNAs bring the amino acids to the ribosome, where they are joined to the growing chain by peptide bonds.32
Folding: Once the polypeptide chain is formed, its characteristic shape is determined by the specific sequence of amino acids. This folding is driven by interactions such as hydrogen bonds and the attraction or repulsion between the side chains (R groups) of the amino acids.145

The resulting three-dimensional structure is essential for the enzyme's specific catalytic function.14