Which of the following will NOT denature a protein?

• A. Heating to 100\degree C
• B. Adding urea
• C. Adding NaCl at physiological concentrations
• D. Changing pH to extreme acidic or basic values

Answer: (C)

Verified step by step guidance

1. Understand the concept of protein denaturation: Protein denaturation refers to the process where a protein loses its native structure due to external stress, such as heat, pH changes, or chemical agents. This disrupts the protein's secondary, tertiary, or quaternary structure, but not its primary structure (sequence of amino acids).
2. Analyze the effect of heating to 100°C: High temperatures can disrupt hydrogen bonds and non-covalent interactions within a protein, leading to denaturation. Proteins are sensitive to heat, and heating to 100°C is a common method to denature them.
3. Examine the role of urea: Urea is a chaotropic agent that disrupts hydrogen bonds and hydrophobic interactions within proteins. It is widely used in laboratory settings to denature proteins by breaking their tertiary and secondary structures.
4. Consider the impact of changing pH to extreme acidic or basic values: Extreme pH values can alter the ionization state of amino acid side chains, disrupting ionic bonds and hydrogen bonds within the protein structure. This can lead to denaturation.
5. Evaluate the effect of adding NaCl at physiological concentrations: Physiological concentrations of NaCl (around 0.9% or 150 mM) do not typically disrupt the native structure of proteins. This is because such concentrations mimic the natural ionic environment in the body, which proteins are adapted to function in. Therefore, adding NaCl at physiological concentrations will NOT denature a protein.