Enzymes and heart attacks 2009-2010 Enzymes: “Helper” Protein molecules.
Enzymes: “Helper” Protein molecules Enzymes Catalysts for biological reactions Most are...
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Transcript of Enzymes: “Helper” Protein molecules Enzymes Catalysts for biological reactions Most are...
Enzymes Catalysts for biological reactions Most are proteins Lower the activation energy Increase the rate of reaction Activity lost if denatured May be simple proteins May contain cofactors such as metal ions
or organic (vitamins)
Chemical reactions of life Processes of life
building molecules synthesis
breaking down molecules digestion
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Nothing works without enzymes! How important are enzymes?
all chemical reactions in living organisms require enzymes to work building molecules
synthesis enzymes
breaking down molecules digestive enzymes
enzymes speed up reactions “catalysts”
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enzyme
enzymeWe can’t live
without enzymes!
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CATALYST CATALYST – – A SUBSTANCE THAT CAUSES A A SUBSTANCE THAT CAUSES A
CHEMICAL REACTION TO HAPPEN MORE QUICKLY.CHEMICAL REACTION TO HAPPEN MORE QUICKLY.
Enzymes work by weakening bonds weakening bonds which which lowers lowers activation energyactivation energy
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EnzymesEnzymes
FreeEnergy
Progress of the reaction
Reactants
Products
Free energy of activationFree energy of activation
Without Enzyme
With Enzyme
Enzymes are proteins Each enzyme is the specific helper to
a specific reaction each enzyme needs to be the right shape
for the job enzymes are named for the reaction
they help sucrase breaks down sucrose proteases breakdown proteins lipases breakdown lipids DNA polymerase builds DNA
Enzymes aren’t used up Enzymes are not changed by the reaction
used only temporarily re-used again for the same reaction with
other molecules very little enzyme needed to help in many
reactions
enzyme
substrate product
active site
Enzyme vocabulary Enzyme
helper protein molecule; catalyst Substrate
molecule that enzymes work on Products
what the enzyme helps produce from the reaction
Active site part of enzyme
that substrate molecule fits into
It’s shape that matters! Lock & Key model
shape of protein allows enzyme & substrate to fit
specific enzyme for each specific reaction
Enzyme Action: Induced Fit Model
Enzyme structure flexible, not rigid Enzyme and active site adjust shape to
bind substrate Increases range of substrate specificity Shape changes also improve catalysis
during reaction
Factors Affecting Enzyme Action: Temperature
Little activity at low temperature Rate increases with temperature Most active at optimum temperatures
(usually 37°C in humans) Activity lost with denaturation at high
temperatures
What affects enzyme action Correct protein structure
correct order of amino acids why? enzyme has to be right shape
Temperature why? enzyme has to be right shape
pH (acids & bases) why? enzyme has to be right shape
Order of amino acids Wrong order = wrong shape = can’t do its job!
DNA
DNA
chain ofamino acids
chain ofamino acids
foldedprotein
foldedprotein
right shape!
wrong shape!
Factors Affecting Enzyme Action: Substrate Concentration
Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant)
Maximum activity reached when all of enzyme combines with substrate
Temperature Effect on rates of enzyme activity
Optimum temperature greatest number of collisions between
enzyme & substrate human enzymes
35°- 40°C (body temp = 37°C) Raise temperature (boiling)
denature protein = unfold = lose shape Lower temperature T°
molecules move slower fewer collisions between enzyme &
substrate
pH Effect on rates of enzyme activity
changes in pH changes protein shape most human enzymes = pH 6-8
depends on where in body pepsin (stomach) = pH 3 trypsin (small intestines) = pH 8
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pH
pH
reac
tio
n r
ate
20 1 3 4 5 6 8 9 10
stomachpepsin
intestinestrypsin
What’s happening here?!
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Enzyme Inhibition
Inhibitors cause a loss of catalytic activity Change the protein structure of an enzyme May be competitive or noncompetitive Some effects are irreversible
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Competitive Inhibition
A competitive inhibitor Has a structure similar to
substrate Occupies active site Competes with substrate for
active site Has effect reversed by increasing
substrate concentration
Noncompetitive Inhibition
A noncompetitive inhibitor Does not have a structure like substrate Binds to the enzyme but not active site Changes the shape of enzyme and active
site Substrate cannot fit altered active site No reaction occurs Effect is not reversed by adding substrate
Allosteric Site – undergoing a change in the shape and activity of a protein (as an enzyme) that results from the combination with another substance at a point other than the chemically active site.