Transcript • What is an enzyme? • Enzyme actions • ‘Lock and key’ hypothesis • Effect of temperature on enzyme action • Effect of pH.

• 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
What is an enzyme?
• a catalyst: speeds up chemical
reactions in the body
• protein
reused
no change
again
Protein
catalyst
• no change after a reaction
 can be reused
• a little amount is enough
• specific
• works within a narrow range of pH and
temperature
Enzyme action: catabolic action
active site
enzyme-substrate
complex
products
substrate
Enzyme
Enzyme
enzyme can be reused again
Enzyme
Enzyme action: anabolic action
substrates
active site
Enzyme
enzyme-substrate
complex
product
Enzyme
enzyme can be reused again
Enzyme
‘Lock and key’ hypothesis
• Explains the specificity 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
lock = substrate
key = enzyme
lock is open
lock and key =
enzyme-substrate complex key has no
change
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)
Effect of temperature on enzyme action
Rate of
enzyme
action
(arbitrary
unit)
Enzyme
activity
Ituntil
thenit decreases
reaches
aincreases
with
maximum
atemperature
further
The optimum
with
riseis
temperature
increase
inin
temperature.
(theaoptimum
temperature).
about
40 oC for most
enzymes in human body.
Temperature (oC)
Effect of pH on enzyme action
Rate of
enzyme
action
(arbitrary
unit)
Enzyme
Different
activity
enzymes
increases
havewith pH
untiltheir
a maximum
own optimum
(the optimum
pH.
pH),
then decreases as pH increases.
pH
Uses of enzymes in daily life
• washing powder
• cleaning solution of contact lens
• meat tenderizers
Summary
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