Final answer:
Commonly observed in beta sheets is the extended polypeptide backbone, which allows for parallel or antiparallel alignments of polypeptide chains, connected by hydrogen bonds.
Step-by-step explanation:
A feature commonly observed in beta sheets is the extended polypeptide backbone. Beta sheets consist of two or more polypeptide chains that are aligned side by side, connected by hydrogen bonding. These polypeptide chains in their extended formation can run in parallel or antiparallel directions. The parallel alignment means that the N-terminals of adjacent chains face the same direction, whereas in antiparallel arrangements, they face opposite directions. Beta sheets play a crucial role in structural proteins and are found in portions of many enzymes.
Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides which have a molecular mass of 10,000 Da or more are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.