ENZYMES
Enzymes - are proteins made of amino acids
- have active sites = places where substrate (food & waste) molecules attach
Draw the enzyme with an active site + a substrate:
- are catalysts b/c they speed up chemical reactions & lower the activation energy
- are reusable b/c they remain unchanged after the reaction
- are specific b/c there is a perfect enzyme for a certain substrate
- have a 3D shape which can be destroyed/denatured w/extreme changes in pH & temperature
Ex)
Catalase  breaks down hydrogen peroxide (waste produced in cells) into
2H2O2 ----> 2H2O + O2
Lactase  breaks down lactose in milk
Protease  breaks down proteins
Lipase  breaks down lipids
Amylase in saliva at pH 7, Pepsin in the stomach at pH 2-3, & Trypsin in the intestines at pH 9
How Enzymes Work?
 Active sites on enzymes = places to which a specific substrate binds
 Enzyme-substrate complexes form (when substrates attach to active sites on the enzymes) to break apart or
put together substances at a fast rate
E
+
S

ES

E
+
P
There are two models of enzyme action
1. lock & key model  substrate & the enzyme fit together perfectly
2. induced-fit model enzymes change shape slightly to accommodate the substrate
Draw figure 4-15
Factors affecting enzyme action
1. Temperature – enzymes work best at certain temperatures, – 37oC is best for human enzymes in the body
2. pH – enzymes work best at certain pH; basic, neutral, and/or acidic environments
3. Substrate & enzyme concentrations – how fast reactions take place depends on how much of the substrate &
enzyme is available.
4. Coenzymes – helpers such as vitamins & minerals