1. Enzymes

2. Characteristics All Enzymes are Proteins
Catalysts – i.e. control the rate of a chemical reaction

3. How Enzymes work
Enzymes bind and hold substrates (aka reactants) in a certain orientation to speed the chemical reaction along
Enzymes change shape as they bind the substrates

4. the binding
substrates +
enzyme-substrate complex
active site

5. the reaction, the release
enzyme-substrate complex
product

6. What about the other way?
substrate
enzyme-substrate complex
enzyme
product

7. Lactase
1926 aa’s long
cell membranes - small intestines
Lactase

8. Beano - alpha galactosidase
breaks down trisaccharides
raffinose – in beans, cabbage
enzyme
not in humans
in bacteria in large intestines
Raffinose is a trisaccharide composed of galactose, fructose, and glucose. It can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Raffinose can be hydrolyzed to D-galactose and sucrose by the enzyme α-galactosidase (α-GAL), an enzyme not found in the human digestive tract.
Humans and other monogastric animals (pigs and poultry) do not possess the α-GAL enzyme to break down RFOs and these oligosaccharides pass undigested through the stomach and upper intestine. In the lower intestine, they are fermented by gas-producing bacteria which do possess the α-GAL enzyme and make carbon dioxide, methane, and/or hydrogen—leading to the flatulence commonly associated with eating beans and other vegetables. α-GAL is present in digestive aids such as the product Beano.
Beano is a product containing the enzyme alpha galactosidase, which is derived from the fungus Aspergillus niger. +

9. another example – glyceraldehyde-3-dehydrogenase

10. re-introducing activation energy
activation energy is the energy required to get a reaction going
activation energy
net energy change

11. How do Enzymes work?
They lower the “activation energy” of the reaction
activation energy is the energy required to get a reaction going
activation energy
net energy change

12. How do they do it? They lower the “activation energy” of the reaction
net energy change

13. Enzyme performance is affected by:
amount of substrate present
temperature pH
Inhibitors
Poisons

14. Enzymes and Amount of Reactants
[ reactants ]  reaction rate because
increased chance of finding molecules
[reactants]  reaction rate because
decreased chance of finding molecules
1. Measure [S] or [P]
2. Combine and Plot
Experiment with amount and rate

15. Enzymes and Temperature
temperature  reaction rate because
increased kinetic energy breaks H-bonds
temperature  reaction rate because
decreased kinetic energy does not break
H-bonds

16. pH Acids – excess Hydrogen ions Bases – excess hydroxyl ions
Neutral – equal numbers of H+ and OH-

17. Enzymes and pH pH changes reaction rate because H-bonds are altered
Experiment with pH and rate

18. Enzymes and pH
each enzyme has an optimal pH; some work best in acidic conditions (<4) (pepsin) while others work best closer to a neutral pH (7)
pH for Optimum Activity Enzyme pH Optimum
Lipase (pancreas) 8.0
Lipase (stomach)
Lipase (castor oil) 4.7
Pepsin
Trypsin
Urease 7.0
Invertase 4.5
Maltase
Amylase (pancreas)
Amylase (malt)
Catalase 7.0

19. Enzymes and Inhibitors

20. Enzymes and Inhibitors
bind to specific enzymes and decrease the reaction rate
Normal substrate
enzyme binding
Competitive inhibitor
binds to the active
site
Noncompetitive inhibitor
binds to the enzyme and
changes its shape

21. Competitive Inhibitors

22. Noncompetitive Inhibitors
A noncompetitive inhibitor is a substance that interacts with the enyzme, but usually not at the active site. The noncompetitive inhibitor reacts either remote from or very close to the active site. The net effect of a non competitive inhibitor is to change the shape of the enzyme and thus the active site, so that the substrate can no longer interact with the enzyme to give a reaction. Non competitive inhibitors are usually reversible, but are not influenced by concentrations of the substrate as is the case for a reversible competive inhibitor. See the graphic on the left.
Irreversible Inhibitors form strong covalent bonds with an enzyme. These inhibitors may act at, near, or remote from the active site. Consequently, they may not be displaced by the addition of excess substrate. In any case, the basic structure of the enzyme is modified to the degree that it ceases to work.
Since many enzymes contain sulfhydral (-SH), alcohol, or acid groups as part of their active sites, any chemical which can react with them acts as an irreversible inhibitor. Heavy metals such as Ag+, Hg2+, Pb2+ have strong affinities for -SH groups.
Nerve gases such as diisopropylfluorophosphate (DFP) inhibit the active site of acetylcholine esterase by reacting with the hydroxyl group of serine to make an ester.
Oxalic and citric acid inhibit blood clotting by forming complexes with calcium ions necessary for the enzyme metal ion activator.

23. Poisons - KCN Specific Irreversible Inhibitor of Cytochrome C Oxidase,
ATP cannot be made
Anaerobic respiration only
Fatal build up - Lactic Acid

24. Poisons - Arsenic
Nonspecific Inhibitor of cellular respiration enzymes
Inhibits glucose break down
Cell death results