Yes, it's true.
Proteins are essentially made up of amino acids. These amino acids form proteins by linking together through peptide bonds. They arrange themselves in a straight chain and then fold into a complex globular structure.
There are 20 different amino acids that play a role in protein synthesis, these are known as proteinogenic amino acids. On the other hand, certain amino acids like ornithine are classified as non-proteinogenic amino acids as they do not participate in the formation of proteins.
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