Which of the following statements most accurately describes the conclusions of the experiment with ribonuclease A? a. Denaturants, such as urea, are sufficient to completely denature ribonuclease. b. Enzyme activity is preserved even when the protein is denatured. c. Protein denaturation is rarely reversible. d. The primary amino acid sequence of ribonuclease is the primary determinant of its three-dimensional structure.
The Correct Answer and Explanation is:
Correct answer: d. The primary amino acid sequence of ribonuclease is the primary determinant of its three-dimensional structure.
The classic experiment involving ribonuclease A was conducted by Christian Anfinsen in the 1950s and 1960s. It demonstrated a fundamental principle of protein chemistry. Ribonuclease A is an enzyme that breaks down RNA. Anfinsen treated ribonuclease A with strong denaturants such as urea and β-mercaptoethanol. Urea disrupted the non-covalent interactions like hydrogen bonds and hydrophobic forces, while β-mercaptoethanol reduced disulfide bridges. As a result, the enzyme unfolded and lost its biological activity.
After the denaturants were removed, the protein spontaneously refolded into its native, active form. This finding revealed that the information required for a protein to fold into its correct three-dimensional structure is entirely contained within its primary amino acid sequence. No other cellular machinery was needed in this in vitro experiment to guide the folding, though in living cells, helper proteins called chaperones often assist.
This conclusion refuted the idea that folding required outside instructions and showed that, at least for some proteins, folding is a thermodynamically driven, self-guided process. It also highlighted the idea that protein structure and function are directly linked to the sequence of amino acids.
Let us evaluate the other choices. Choice a is true but not the most insightful conclusion. Choice b is incorrect because enzyme activity is typically lost when the protein is denatured. Choice c is incorrect because the experiment showed that denaturation can be reversible under the right conditions. Therefore, choice d is the most accurate and meaningful conclusion drawn from Anfinsen’s experiment.
