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Polypeptides are linear chains of amino acids linked by peptide bonds. A polypeptide becomes a protein when it folds into a specific three-dimensional structure that is biologically active, meaning it can perform its specific function in the cell. Proteins are functional biological molecules that often consist of one or more polypeptides that have folded into a unique, functional three-dimensional structure. Proteins can be made of a single polypeptide chain or multiple polypeptide subunits. The complexity, folding, and post-translational modifications of these chains contribute to the functional diversity of proteins. Therefore, while all proteins are essentially polypeptides because they are made from amino acid chains, not all polypeptides qualify as proteins. Some polypeptides might act as hormones, toxins, or signaling molecules without adopting the complex structures or functions typically associated with proteins. Problem: Which of the following statements is true regarding polypeptides and proteins? A) All polypeptides are proteins, but not all proteins are polypeptides. B) All proteins are polypeptides, but not all polypeptides are proteins. C) Proteins and polypeptides are exactly the same. D) Proteins are made of nucleotides, while polypeptides are made of amino acids.
