A Level Biology Practice Exam

What is the tertiary structure of a protein characterized by?

1. the sequence of amino acids that make up the protein

2. the complete arrangement of all polypeptide chains

3. interactions between R-groups forming hydrogen bonds and disulfide bridges

4. the simple folding of the polypeptide chain into alpha-helices and beta-sheets

The correct answer is: interactions between R-groups forming hydrogen bonds and disulfide bridges

The tertiary structure of a protein is characterized by the overall three-dimensional shape that arises from the interactions between the side chains or R-groups of the amino acids in the polypeptide chain. These interactions can include hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges, which collectively influence how the protein folds and stabilizes its structure. This level of structure is crucial because it determines the protein's functionality and interactions with other molecules. The precise folding and arrangement driven by these interactions lead to the unique characteristics of each protein, allowing it to perform its specific biological role within the organism. Other aspects of a protein's structure are related to different levels of organization. The sequence of amino acids pertains to the primary structure, while the complete arrangement of all polypeptide chains refers more to quaternary structures, which involve multiple polypeptide units. The simple folding into alpha-helices and beta-sheets describes the secondary structure, which is just one component contributing to the final tertiary form.