Final answer:
The secondary structure of proteins includes the alpha-helix and beta-pleated sheet, which are stabilized by hydrogen bonds. Examples include keratin in hair, which comprises alpha-helices. This structure is essential for the function and shape of proteins.
Step-by-step explanation:
The main answer to the question 'Which of these illustrates the secondary structure of a protein?' is that the secondary structure refers to the local folding of the polypeptide backbone of a protein into organized structures, mainly the alpha-helix and beta-pleated sheet. An alpha-helix is formed by hydrogen bonds between every fourth amino acid which makes the polypeptide chain coil into a spiral. A beta-pleated sheet is comprised of amino acids arranged side-by-side in a sheet-like formation, again stabilized by hydrogen bonds. For example, keratin, found in hair and nails, primarily consists of alpha-helices.In more than 100 words, the explanation of the secondary structure includes the importance of hydrogen bonds in maintaining the shape of these structural motifs. The oxygen atom of the carbonyl group in one amino acid forms hydrogen bonds with an amino acid that is four residues away for the alpha-helix, whereas in beta-pleated sheets, hydrogen bonds are formed between amino acids on adjacent strands of the sheet. This level of structure is critical to the overall three-dimensional shape of the protein which, in turn, determines its function.In conclusion, understanding the secondary structure of proteins is vital for grasping how proteins fold and function. It provides insights into their durability and role in various biological processes and is essential knowledge for students studying biology and biochemistry.