Mar 31, 2015
• What is an enzyme?
• Enzyme actions
• ‘Lock and key’ hypothesis
• Effect of temperature on enzyme action
• Effect of pH on enzyme action
• Uses of enzymes in daily life
• protein
Protein
• a catalyst: speeds up chemical reactions in the body
• no change after a reaction
• a little amount is enough• specific
• works within a narrow range of pH and temperature
no changereused again
catalyst
What is an enzyme?
can be reused
Enzyme action: catabolic action
Enzym e Enzym e
enzyme-substrate complex
products
enzyme can be reused again
Enzym e
active site
substrate
Enzyme action: anabolic action
enzyme can be reused again
active site
substratesproductenzyme-substrate
complex
Enzym e Enzym e Enzym e
‘Lock and key’ hypothesis• Explains the specificityspecificity of enzyme actions
• Each key opens only one lock
• Each enzyme acts on one or a few substrates that fits into its active site
‘Lock and key’ hypothesis
key = enzyme
lock = substrate
lock and key =enzyme-substrate complex key has no
change
lock is open
Effect of temperature on enzyme action
• Works slowly at low temperature (inactive)
• Does not work at high temperature (denatured)
• Works best at a narrow range of temperature (optimum temperature)
Enzyme activity increases with a rise in temperatureIt then decreases with a further increase in temperature.
Effect of temperature on enzyme action
Temperature (oC)
Rate of enzyme action(arbitrary unit)
The optimum temperature is about 40 oC for most enzymes in human body.
until it reaches a maximum (the optimum temperature).
Enzyme activity increases with pH until a maximum (the optimum pH), then decreases as pH increases.
pH
Rate of enzyme action(arbitrary unit)
Different enzymes have their own optimum pH.
Effect of pH on enzyme action
• washing powder
• cleaning solution of contact lens
• meat tenderizers
Uses of enzymes in daily life
Enzymes• are special proteins that speed up chemical
reactions inside organisms (a biological catalyst)• take part in both catabolic and anabolic reactions• are specific• whose specificity explained by ‘lock and key’
hypothesis• whose activity changes with temperature and pH
Summary