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Regents Biology
2.4 – Chemical Reactions and Enzymes
Regents Biology
Chemical reactions of life § Processes of life involve
- building molecules (forming bonds)
- breaking down molecules (breaking bonds)
+
+
Regents Biology
Dehydration vs. Hydrolysis § dehydration synthesis (synthesis)
§ hydrolysis (digestion)
Regents Biology
Chemical Reactions and Energy § Chemical reactions that release energy often occur
spontaneously.
Regents Biology
Chemical Reactions and Energy § Chemical reactions that absorb energy will NOT occur
without a source of energy.
§ Activation energy – energy needed to get reactants to become unstable enough to react with each other (for both types of reactions)
Regents Biology
Activation energy § is energy that moves the reaction over an “energy
hill” § How is this energy supplied? § Heat
glucose
Not a match! That’s too much energy to expose living cells to!
Regents Biology
Reducing Activation energy § But applying heat to the whole system might be bad. § How else to supply this energy? § Catalysts (enzymes) reduce the amount of energy to
start a reaction.
reactant
product
uncatalyzed reaction
catalyzed reaction
NEW activation energy
Pheeew… that takes a lot
less energy!
Regents Biology
What’s going here?
Regents Biology
How important are enzymes? § ALL chemical reactions in living organisms require
energy to work.
§ Enzymes reduce activation
energy, thus speed up reactions Ex: catalase helps break down hydrogen peroxide fast
Regents Biology
Enzymes in detergents
Regents Biology
What else about enzymes? § Enzymes are mostly proteins. § Each enzyme helps a specific reaction. § Each enzyme needs to be the right
SHAPE for the job. § Enzymes are named for the reaction
they help. Ex:
§ sucrase breaks down sucrose § proteases breakdown proteins § lipases breakdown lipids § DNA polymerase builds DNA
Oh, I get it! They end in -ase
Regents Biology
Sucrase
§ Enzymes are NOT changed or used up by the reaction.
Regents Biology
It’s SHAPE again! § Lock and Key Model - shape of protein allows the
substrate to fit into the enzyme so that a chemical reaction can occur.
Regents Biology
Wrong shape? § insecticide Malathion § Penicillin
Regents Biology
What affects enzyme action § Correct order of amino acids - why? - enzyme has to be right
shape § Temperature - why? - enzyme has to be right
shape § pH - why? - enzyme has to be right
shape
Regents Biology
Order of amino acids § Wrong order = wrong shape = can’t do its job!
chain of amino acids
chain of amino acids
folded protein
folded protein
right shape!
wrong shape!
Regents Biology
Effect of Temperature on Enzyme Activity - ideal (optimum) temperatures allow for greatest number
of collisions between enzyme and substrate - too high or too low temperatures cause proteins to lose
their shape (denaturation)
37° temperature
reac
tion
rate
Regents Biology 7
Effect of pH on Enzyme Activity
pH
reac
tion
rate
2 0 1 3 4 5 6 8 9 10
stomach pepsin
intestines trypsin
11 12 13 14
- optimum pH for most human enzymes is around 6-8 - too high or too low pHs cause proteins to lose their
shape (denaturation) although…
Regents Biology
Enzymes
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