Final answer:
Polypeptides possess a free amino group at the N-terminal end and a free carboxyl group at the C-terminal end, resulting from peptide bonds formed between amino acids during protein synthesis.
Step-by-step explanation:
Polypeptides have polarity, which means one end of the chain has a distinct chemical structure compared to the other end. This is due to the sequential nature of the peptide bonds that join amino acids together. At one end of the polypeptide, there exists a free amino group (–NH₂), which is referred to as the N-terminal. At the other end, there is a free carboxyl group (–COOH), known as the C-terminal. During the process of protein synthesis, amino acids are linked by dehydration synthesis reactions, forming peptide bonds where the carboxyl group of one amino acid and the amino group of the next combine, releasing a molecule of water.
It's important to note that additional amino acids are always added to the C-terminal end as the polypeptide chain grows. The polypeptide backbone is consistent across all proteins, with differing R groups (side chains) that confer uniqueness to each polypeptide. Polypeptides differ from fully functional proteins in that proteins may be composed of one or more polypeptide chains and often require post-translational modifications to become functional.