The stability of a protein is not simply the sum of the free energies of formation of the many weak interactions within it. In general, the protein conformation with the lowest free energy (that is, the most stable conformation) is the one with the maximum number of weak interactions. Yet, because they are so numerous( reason), the weak interactions predominate as a stabilizing force in protein structure. Individual covalent bonds, such as disulfide bonds linking separate parts of a single polypeptide chain, are clearly much stronger than individual weak interactions.The association of multiple polypeptides to form quaternary structures also relies on these weak interactions For all proteins of all organisms, weak interactions are especially important in the folding of polypeptide chains into their secondary and tertiary structures.Outside the cell, the environment is often more oxidizing, and disulfide formation is more likely to occur. (Answer)The environment within most cells is highly reducing due to high concentrations of reductants such as glutathione, and most sulfhydryls will thus remain in the reduced state. Many proteins do not have disulfide bonds.The chemical interactions that counteract these effects and stabilize the native conformation include disulfide (covalent) bonds and the weak (noncovalent) interactions and forces : hydrogen bonds, the hydrophobic effect, and ionic interactions. This entropy, along with the hydrogen-bonding interactions of many groups in the polypeptide chain with the solvent (water), tends to maintain the unfolded state.In the context of protein structure, the term stability can be defined as the tendency to maintain a native conformation.Proteins in any of their functional, folded conformations are called native proteins.The spatial arrangement of atoms in a protein or any part of a protein is called its conformation.A Protein’s Conformation Is Stabilized Largely by Weak Interactions
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