Question

protein denaturation – what is it, how does it happen (various answers here), chemical reason it occurs (if applicable) (again, multiple answers here)

Answer 1

• Hydrogen bonds - weak bonds between slightly positively charged hydrogen and slightly negatively charged atoms (such as oxygen).
• Electrostatic interactions - weak attractive forces between charged regions of the protein, including only small charges resulting from polar bonds.
• Disulphide bridges
• Hydrophobic interactions

• Hydrogen bonds and electrostatic interactions are dependent on interactions between charges. pH is a measure of the concentration of hydrogen ions, which are positively charged. If there were more hydrogen ions in the solution than the protein was designed for, these ions would compete for the interactions holding the protein together, as well as protonating groups that need to be deprotonated to form important intramolecular interactions (eg nitrogen). Equally, if there were too few hydrogen ions in the solution, the same interactions would disrupted by the relatively high concentration of hydroxide (OH) ions, and important protonated groups may become deprotonated.
• Increasing the temperature increases the energy of the bonds and atoms in the protein, to the point at which there is enough energy to overcome the force of the intramolecular reactions, resulting in them breaking.
• Disruption of the interactions in any case will lead to some of the protein losing its ability to be held in a certain shape, which then reduces it's catalytic activity (as catalytic activity relies on the shape). The loss of activity will be proportional to the extent of the disruptions, which will in turn be proportional to the extent of the change in pH or temperature.
• Disulphide bonds would also be reduced (broken) at very low pH, and broken at extremely high temperatures (though other interactions will have already broken and destroyed activity before this temperature/pH is reached).