Which of the following best describes polypeptides?

Polypeptides are best described as chains of amino acids linked together. This definition captures the fundamental structure of polypeptides, which are formed through the process of polymerization of amino acids. During protein synthesis, amino acids are connected by peptide bonds, forming a linear chain, which is what a polypeptide is.

As these chains grow, they can then fold into specific three-dimensional shapes, ultimately becoming functional proteins. However, at the stage of simply being a chain of amino acids, the structure has not yet fully formed into the complex configurations that characterize mature proteins. The other options refer to different biological molecules and processes: carbohydrates refer to sugars and starches, nucleotides relate to the building blocks of nucleic acids like DNA and RNA, and fully folded proteins represent a later stage of the polypeptide's life cycle. Thus, the correct choice accurately encapsulates the essence of what polypeptides are.