gly-arg-ala-ser-phe-gly-asn-lys-trp-glu-val

The amino acid sequence is the linear arrangement of amino acids in a protein or polypeptide chain, defined by the specific genetic code of an organism. The sequence in which these amino acids are connected dictates the three-dimensional structure and eventual function of the protein formed. Understanding the amino acid sequence of a protein is akin to reading the letters that make up a sentence; each amino acid can be seen as an individual 'word' that, when placed in the correct order, conveys a specific meaning or function.

Consider the given polypeptide sequence: gly-arg-ala-ser-phe-gly-asn-lys-trp-glu-val. Each abbreviation represents an amino acid building block, and their order is crucial. For example, switching 'ser' (Serine) with 'trp' (Tryptophan) would result in a distinct polypeptide with potentially different characteristics. Hence, the 'grammar' of the polypeptide chain – its amino acid sequence – is essential for ensuring that the protein can carry out its biological roles effectively.

Peptide bonds are the chemical backbone that links amino acids together within a polypeptide chain. These bonds form in a dehydration synthesis reaction: a carboxyl group of one amino acid reacts with the amino group of another, releasing a molecule of water and creating the peptide bond in the process. The repeating chain of peptide bonds gives rise to the primary structure of a protein.

Understanding peptide bonds helps us grasp how proteins are constructed. These bonds are strong, providing the durability needed to maintain protein structure under a variety of physiological conditions. However, they are also susceptible to enzymatic cleavage, which means that proteins can be broken down when they're no longer needed or when cells want to regulate biological processes.

Protein structure is the intricate architecture formed by the polypeptide chain, determining the function of the protein. The overall shape of the protein is built upon four levels of structure – primary, secondary, tertiary, and quaternary. The primary structure is simply the sequence of amino acids. The secondary structure refers to regular, recurring arrangements in certain segments of the amino acid chain, such as alpha helices and beta sheets, which are stabilized by hydrogen bonds.

The tertiary structure is the full three-dimensional folding of the polypeptide chain, influenced by interactions like hydrophobic interactions, ionic bonds, disulfide bridges, and van der Waals forces. In some proteins, multiple polypeptide chains, or subunits, combine to form the quaternary structure. Each level of protein structure is crucial, as it affects accessibility of functional sites and thus the biological activity of the protein. Disruption at any structural level can lead to loss of function and potentially, disease.