In the polypeptide Tyr-Gly-His-Phe-Val, identify the N-terminal and the C-terminal residues.

At the heart of understanding polypeptide chains is grasping the importance of the N-terminal residue, the very first building block in this complex structure. Like the opening chapter of a book, the N-terminal provides the initial context for what's to come. It is the amino acid with a free amino group (-NH2) that isn't involved in a peptide bond with another amino acid. This characteristic free group is what defines the starting point of the polypeptide.

Reflecting on the Tyr-Gly-His-Phe-Val peptide from our exercise, by examining the chain, we identify tyrosine (Tyr) as the N-terminal residue. It's helpful to remember that during synthesis in living organisms, polypeptides are assembled starting from the N-terminal. This order is crucial in protein biosynthesis and dictates the final three-dimensional structure of the protein.

In contrast to the N-terminal, the C-terminal residue is at the opposite end of the polypeptide chain. It is marked by a free carboxyl group (-COOH) that is not involved in a peptide bond. The C-terminal is the final amino acid added to the growing polypeptide during protein synthesis and acts like a period at the end of a sentence.

For the polypeptide presented, valine (Val) serves as the C-terminal residue. Knowing the C-terminal end can be critical, as certain modifications after protein synthesis occur at this site, which can influence the protein's stability and function. Such awareness is vital for understanding the lifecycle of proteins within biological systems.

A peptide bond is a covalent chemical bond that connects two amino acid residues. This bond is formed when the carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water - a process known as dehydration synthesis.

The robustness of peptide bonds makes polypeptides stable structures, ensuring that proteins can perform their functions effectively. Each bond exists between the carbon atom of one amino acid and the nitrogen atom of the next. These bonds are the backbone of the polypeptide chain, and understanding their chemistry is critical for comprehending protein function and structure.

The orientation of amino acids in a polypeptide chain is unidirectional and precise, playing a pivotal role in the protein's characteristics. It is essential to understand that each amino acid is distinct, with a specific side-chain that imparts unique chemical properties.

In our polypeptide example, Tyr-Gly-His-Phe-Val, the amino acids are oriented from the N-terminal Tyr to the C-terminal Val. The precise order and orientation of these amino acids are paramount, as they determine the function and three-dimensional conformation of the resultant protein. It's this sequential arrangement that establishes the primary structure of proteins and dictates their ultimate roles within biological systems.