Download Enzymes and Activation Energy

Enzymes and Activation Energy
• The diagram, to the right, shows hypothetical
relationships between temperature and enzyme
activity for a human and for a thermophilic (heat
loving) bacteria.
• Notice the optimum (best) activity level for each enzyme matches the
environment that the enzyme has to work in.
• Human enzymes generally work best at our temperature (37°C) while
the thermophilic bacteria's enzyme works best at a higher temperature.
• Indeed some of these thermophilic organisms live quite nicely at the
boiling point of water.
• Enzymes and activation energy
• All chemical reactions require some amount of energy to get them started.
• This energy is called activation energy.
• The way enzymes operate is by effectively lowering the amount of activation
energy required for a chemical reaction to start.
• Sometimes this happens because enzymes might weaken a covalent bond
within a substrate molecule.
• In other cases this lowering of activation energy seems to happen because the
enzyme holds the substrate molecules in a particular position that increases
the likely that the molecules are going to react.
• Energy hill diagrams are a good way to
visualize the effect of enzymes on
activation energy.
• The diagram shows time on the horizontal
(side-to-side) axis and the amount of
energy in the chemicals involved in a
chemical reaction on the vertical (up-and-down) axis.
• The point if this diagram again is that without the enzyme, much more
activation energy is required to get a chemical reaction to take place.
kMc/ym 07 http://staff.jccc.net/pdecell/metabolism/enzymes/enzymes.html