Mr. Safford’s Biological Sciences
ENZYMES
WHAT ARE ENZYMES?
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All enzymes are globular
proteins thus spherical in
shape
Control biochemical
reactions in cells
They have the suffix "-ase"
WHAT ARE ENZYMES?
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Intracellular enzymes are found inside the cell
Extracellular enzymes act outside the cell (e.g. digestive
enzymes)
Enzymes are catalysts → speed up chemical reactions
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Reduce activation energy required to start a reaction
between molecules
Substrate molecules (reactants) are converted into products
Reaction may not take place in absence of enzymes (each
enzyme has a specific catalytic action)
Enzymes catalyze a reaction at max. rate at an optimum
state
HOW DO THEY WORK?
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Lock and key theory
 Only
one substrate (key) can fit into the enzyme's
active site (lock)
 Both structures have a unique shape
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Enzyme is not used (reusable) up in the
reaction (unlike substrates)
HOW DO THEY WORK?
HOW DO THEY WORK?
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Let’s See it in Action!
3 THINGS THAT AFFECT ENZYME EFFECTIVENESS
1.
Changes in pH
Affect attraction between substrate and enzyme
 Ionic bonds can break and change shape → enzyme is
denatured
 Charges on amino acids can change → Enzyme
Substrate complex cannot form
 Optimum pH (enzymes work best)
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 pH
7 for intracellular enzymes
 Acidic range (pH 1-6) in the stomach for digestive enzymes
(pepsin)
 Alkaline range (pH 8-14) in oral cavity (amylase)
2.
Temperature
Increased Temperature
 Increases speed of molecular movement → increased
chances of molecular collisions → more ES complexes
 Enzymes have optimum temp. for their action (usually 37°C
in humans)
 Just above ≈42°C, enzyme is denatured due to the breaking
Hydrogen bonds and higher temps. break covalent bonds
 Denaturation -the loss of appropriate structure rendering
the enzyme inactive.
 Shape is changed → active site can't be used, ever again
DENATURED
Decreased Temperature
Enzymes become less and less active, due to
reductions in speed of molecular movement
 Below freezing point
 Inactivated, not denatured
 Regain their function when returning to normal
temperature
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A typical graph of rate against temperature might
look like this:
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3.
Concentrations of Substrate and Enzyme
4.
The presence of inhibitors
 Enzyme
inhibitors are substances which alter the
catalytic action of the enzyme and consequently
slow down, or in some cases, stop catalysis.
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three common types of enzyme inhibition –
Competitive-compete for active site
 Non-competitive- bind to enzyme somewhere other than the
active site and change the active site
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