temperature would be so high that the cell would die before the activation energy
threshold could be reached.
Enzymes are needed for metabolism to occur in a timely fashion. The activ-
ity of enzymes depends upon how closely their functional sites fit with their
substrates. The shape of the enzyme’s functional site is called its active site. This
site fits in regard to the shape of the substrate. The active site of the enzyme
compliments the shape of its substrate. A perfect fit does notoccur until the
substrate and enzyme bind together to form an enzyme-substrate complex.
PH
The chemical denaturing of enzymes is caused by very high or very low pH.
H+ions that are released from acids and accepted by bases interfere with hydro-
gen bonding. If we change the pH of the environment of unwanted microorgan-
isms, we can control their growth by denaturing their proteins. An example is
vinegar, which is acetic acid; it has a pH of 3.0. Vinegar acts as a preservative
in “ pickling” vegetables. Ammonia has a pH of 11. Ammonia is a base, and for
this reason we use ammonia as a cleaner and disinfectant.
ENZYME SUBSTRATE CONCENTRATION
As substrate concentrations increase, enzyme activity also increases. When all
enzyme binding sites have bound to a substrate, the enzymes have reached their
saturation point. If more substrate is added, the rate of enzyme activity will not
increase. One way organisms regulate their metabolism is by controlling the
quantity and timing of enzyme synthesis.
The Right Influences: Factors Affecting Enzymes
The ability of an enzyme to lower the activation required for metabolism is
influenced by three factors. These are pH, temperature, and the concentration of
enzyme, substrate, and product.
Temperature
Changes in temperature change the shape of the active site, and therefore, influ-
ence the fit between the active site and the substrate. Enzymes in humans work
best at about 37 degrees Celsius. This is the same temperature at which en-
zymes work best for some pathogenic microorganisms, too. Once the tempera-
CHAPTER 5 The Chemical Metabolism^91