1.3 biochemical reactions · cofactors/coenzymes cofactors: nonprotein inorganic substances zn2+,...
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Enzymes (p.36-40)
1.3 Biochemical Reactions
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Chemical reaction
Activation energy:
certain amount of energy required to begin any
chemical reaction
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Enzyme
name usually ends in –ase (eg. Amylase)
protein catalyst
speeds up a chemical reaction without being
consumed
reduces the activation energy
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Activation Energy is reduced by:
Bring two substrates together in correct position
stretch/bend bonds
Transfer electrons
Add/remove hydrogen ion
destabilize
substrate
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Enzyme Structure
very specific
Specific 3-D shape allows binding to one specific substrate
Specific function for specific biochemical reaction
Enzyme + Substrate Enzyme-substrate complex
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Induced-Fit Model
1. substrate binds to the active siteof enzyme
2. functional groups come close
3. enzyme protein change its shape better grip
4. Forms enzyme-substrate complex
5. reaction occurs
6. products less affinity for enzyme released
7. enzyme returns to original shape recycled
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Factors affecting Enzyme activity
1. Temperature
2. pH
3. Enzyme concentration
4. Substrate concentration
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1. Temperature
Too low: bonds not flexible enough for substrate to
fit properly
Too high: enzyme denatures
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2. pH
Bonds sensitive to H+ concentration
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3. Enzyme concentration
More enzymes
more likely to
collide with substrates
increased rate of
reaction
Can saturate
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4. Substrate Concentration
More substrates
increased rate of
reaction
Until Point of saturation
(all enzymes of occupied)
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Enzyme - Regulation Mechanisms
Cofactors/Coenzymes
Competitive inhibitors
Non-Competitive
inhibitors
Allosteric Changes
Feedback Inhibition
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Cofactors/Coenzymes
Cofactors:
nonprotein
inorganic substances
Zn2+, Mn2+
Coenzyme:
organic substances
NAD+
derivative of Vitamin B3
electron carrier in cellular respiration
NADP+
electron carrier in photosynthesis
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Cofactors/Coenzymes
placed within the
active site of the
enzyme
helps to draw
electrons from the
substrate molecules.
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Competitive Inhibitors
similar to substrate
block active site
reversible
overcome by
increasing [substrate]
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Noncompetitive Inhibitors
not compete for active site
bind to another site on enzyme (allosteric site)
change shape
prevents substrate from binding
DDT, poison, inhibits enzymes of nervous system
Video: Competitive and non-competitive inhibition.mp4.mp4
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Allosteric Changes
Allosteric site:
receptor site some distance away from the active site
Allosteric activator:
stabilizes active form of enzyme
Allosteric inhibitor:
stabilizes inactive form of enzyme
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Feedback Inhibition
for a series of sequential reactions
each step has specific enzymes
a product in later steps inhibits enzyme for earlier step
binds to allosteric site of enzyme using weak bonds
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Feedback Inhibition
Cells use this process to
prevent overproduction
of a certain product