residues from the enzyme form interactions with the substrate to help weaken bonds and speed up the ROR
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2 models for enzymes
lock & key. Induced fit model
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which one happens in reality
induced fit
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enzymes are
stereospecific
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For a reaction to be favourable normally ....
the products need to be at a lower energy state/level
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Ea
activation energy - energy required to start the reaction
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Catalysts
lower the Ea
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Non covalent catalysis
Proximity effect- substrate conformational orientations, activation of bonds via space interactions
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covalent catalysis
proximity effect & covalent interactions - activation of bonds via ion/group transfer between substrate and enzyme
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types of catalysis (if no cofactor is present)
acid-base. nucleophilic , electrophillic
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Michaelis - Menton equation
V= Vmax[S]/Km+[S]
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each term in the MM
V = ROR , Vmax= the maximum rate , Km= half the Vmax , [S] = sub conc
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2 steps involved in enzyme reactions
1. binding of the enzyme and substrate 2. conversion of Ensyme sub complex -> product + enzyme
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Assumptions of the MM equation (2)
1. Substrate is always in xs 2. system is always in steady state
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steady state
ESC is being formed at the same rate it is being broken down
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Km
half the Vmax- the substrate conc req for enzyme to reach half the vmax
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In rate experiments when will we measure the rate
at the start- we measure initial velocity - since enzymes will become saturated eventually
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The Vmax
will never actually be reached - it is an assymptote - it is theoretical
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A Vmax for a give enzyme is
constant
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the smaller the KM
the better the enzyme
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Turn over number is a measure of
catalytic activtity - direct measure of product production under saturated sub conditions. it is the max no of sub molecules converted per enzyme in a given time
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Catalytic effiecienty
Kcat/Km
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reversible inhibition
non covalent interactions , ionic and h bonds
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irreversible inhibition
covalently binds to the enzyme
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Types of reversible inhibition
competitive, uncompetitive , mixed , non competitive
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competitive
sub and inhibitor cannot bind at the same time, Km increase , Vmax will same
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Uncompetitve
inhibitor binds to the ESC- Km will decrease, Vmax will decrease
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Mixed
inhibitor can bind at same time as substrate - Km will decrease as will Vmax
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