life11e_ch03

Environmental conditions affect protein structure

Because they are determined by weak forces, the three-dimensional structures of proteins are influenced by environmental conditions. Conditions that would not break covalent bonds can disrupt the weaker, noncovalent interactions that determine secondary, tertiary, and quaternary structure. Such alterations may affect a protein’s shape and thus its function. Various conditions can alter the weak, noncovalent interactions:

Increases in temperature cause more rapid molecular movements and thus can break hydrogen bonds and hydrophobic interactions.
Changes in pH can change the pattern of ionization of exposed carboxyl and amino groups in the R groups of amino acids, thus disrupting the pattern of ionic attractions and repulsions.
High concentrations of polar substances such as urea can disrupt the hydrogen bonding that is crucial to protein structure. Urea was used in the experiment on reversible protein denaturation shown in Figure 3.10.
Nonpolar substances may also disrupt normal protein structure in cases where hydrophobic interactions are essential to maintain the structure.