Download Enzymes and How They Work

Enzymes and How They Work
A. Enzymes are​:
1) Proteins- long folded chain of amino acids
2) Catalysts- chemicals which speed up a reaction without being consumed
B. Properties of enzymes:
1) Speed up reactions
2) Can be used over and over, only needed in small amount
3) Decrease amount of energy needed to start a reaction (activation energy)
4) Specific to a substrate based on its shape – “Lock and Key”
5) Sensitive to temperature and pH
C. How do enzymes work?
For an enzyme to catalyze (speed up) a reaction:
1) The enzyme must form a temporary association with a substance which it will act on. This
substance is known as a substrate.
Substrate- the substance that is acted on by an enzyme
2) The enzyme must bind to the substrate at the enzyme’s “active site” to form one structure.
This is known as the enzyme-substrate complex.
Enzyme-substrate complex- temporary union of enzyme and substrate
Active site- where the substrate can attach to the enzyme
3) The enzyme-substrate complex must stay together as the enzyme reacts on the substrate.
4) The enzyme and products must separate and leave the enzyme unchanged.
S+E
→ ​ES complex
D. Models of Enzyme Action
→​
​
E+P
​1) Lock and Key Theory- enzymes are very specific so that only ONE substrate fits into the
active site of ONE enzyme
2) Induced Fit Model- enzymes are relaxed and change to fit the shape of the substrate to
catalyze the reaction
E. Factors affecting enzymes
1) ​pH
a) most enzymes work best at pH of 7
b) _acidic or basic_____ environments slow enzyme activity
c) some enzymes prefer a more acid or basic environment
1) pepsin (in the stomach) prefers a pH of 2
2) trypsin prefers a pH of 8
2) ​Temperature
a) most enzymes work best at _________37 C________
b) at very low temperatures, enzyme activity ____slows down_____
c) at very high temperatures, enzymes become DENATURED
DENATURED- enzyme unravels and the active site changes shape, becomes inactive
3) ​Concentration of substrate
a) The rate of reaction can be increased by adding substrate until it reaches its maximum
(enzymes are “full”)
F. ​Naming Enzymes
1) Enzymes are specific and named for their substrate
___protease__ → proteins
__amylase__ → amylose (starch)
__lipase__ →
lipids
__nuclease__ → nucleic acids
G) Competitive inhibition​ – the structure of an inhibitor resembles the structure of the
substrate which can block the active site.