Answer both parts of #1 Most globular proteins denature and lose their activity when briefly heated to 65 °C. However, globular proteins that containmultiple disulfide bonds often require longer heat exposure at higher temperatures to denature them. One such protein is bovinepancreatic trypsin inhibitor (BPTI). BPTI has 58 amino acid residues in a single peptide chain and contains three disulfidebonds. After cooling a solution of heat denatured BPTI, the protein regains its activity.What is the molecular basis for this property of BPTI?Disulfide bonds make BPTI more rigid at high temperatures than low temperatures.Disulfide bonds protect BPTI from peptide bond hydrolysis during heating.Disulfide bonds lower the optimal temperature of the reaction BPTI participates in.Disulfide bonds prevent the complete unfolding of BPTI at high temperatures. Question 1 of 10 >O Macmillan LearningSome proteins are rich in disulfide bonds, and their mechanical properties such as tensile strength, viscosity, hardness, etc.,correlate with the degree of disulfide bonding.Glutenin, a wheat protein rich in disulfide bonds, imparts the cohesive and elastic character of dough made from wheat flour.Similarly, the hard, tough nature of tortoise shell results from the extensive disulfide bonding in its a-keratin.What is the molecular basis for the correlation between disulfide-bond content and mechanical properties of the protein?Proteins containing disulfide bonds have a longer half-life in the cytosol.Disulfide bonds give rigidity to a protein and prevent any conformational changes.Proteins containing disulfide bonds participate in more protein-protein interactions.Disulfide bonds act as intramolecular cross-links that stabilize proteins.

The coupling of 2 thiol (-SH) groups results in the formation of a disulfide bond, which is a covalent bond between two sulfur atoms (-S-S-). One of the twenty protein amino acids, cystine, has a -SH group in its side chain and dimerizes to cystine very quickly in aqueous solution by generating a disulfide bond. Disulfide bonding between cysteine residues are necessary for protein folding in many protein molecules.The Correct option is : Disulfide bonds prevent the complete unfolding of the BPTI at high temperatures. The disulphide bonds in the 58 amino acids that make up the bovine pancreatic trypsin inhibitor, which are disrupted with heating, render the inhibitor ineffective. However, it returns to its native conformation after cooling because the interior structure begins forming hydrogen and disulfide bonds. As a result, the BPTI's activity restarts. It is hypothesized that structural characteristic helps make intracellular proteins more soluble. On the other hand, extracellular proteins must be strong to move around in the extracellular environment. By reducing the chain entropy of the unfolded state, disulphide bonds significantly aid in the stabilization of proteins. When intrachain disulphide bonds are intact, the refolding of small globular proteins occurs almost spontaneously, but refolding from reduced and denatured states necessitates the right redox conditions. In order to prevent irreversible denaturation under heating conditions, it is essential to preserve wild-type disulphide linkages. Thus, Cystine residues in disulfide bonds prevent the complete unfolding of the protein. Other options are incorrect: Disulfide bonds make BPTI more rigid at high temperatures than low temper : This option is incorrect because at high temperature in which the breaking down of hydrogen, disulphide bonds occurs leads to denaturation of proteins. Disulfide bonds protect BPTI from peptide bond hydrolysis during heating: This option is incorrect because disulfide bonds at high temperature do not protect BPTI from peptide bond hydrolysis. Disulfide bonds lower the optimal temperature of the reaction BPTI participates in: This option is incorrect because disulfide bonds lower the optimal temperature of the reaction it increases the thermal stability of protein.Conclusion: Disulfide bonds prevent the complete unfolding of the BPTI at high temperatures, which is a molecular basis of BPTI for restoring its activity.