Enzymes
Metabolism and Enzymatic Reactions
Metabolism
• All living things need energy• This energy is used by organisms to develop,
grown and reproduce• Energy is used in chemical reactions to
perform this development, growth and reproduction.
• METABOLISM is the sum of all the biochemical reactions that occur in a cell.
• The energy-producing reactions within cells generally involve the breakdown of complex organic compounds to simpler compounds. These reactions release energy and are called catabolic reactions.
• Anabolic reactions are those that consume energy while synthesizing compounds.
• ATP produced by catabolic reactions provides the energy for anabolic reactions. Anabolic and catabolic reactions are therefore coupled (they work together) through the use of ATP.
ATP ADP + Pi
Energy
Energy
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An anabolic reaction
A catabolic reaction
Catabolic and Anabolic Reactions
• Metabolic reactions have – REACTANTS, which are the substances that participate in a reaction,
and – PRODUCTS, which are the resulting substances
A+B→C+D
• Within cells many reactions are often linked together to create the products a cell needs from the reactants it is able to acquire. These chains of reactions are called METABOLIC PATHWAYS.
A→B→C→D→E→F→G
• In this process the products from one reaction become the reactants for the next reaction.
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F
A B C D E
• Metabolic pathways can branch so that a product like D can become the reactant in two different types of reactions
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Enzymes
enzyme 1 enzyme 2 enzyme 3 enzyme 4
Fenzyme 5
A B C D E
• ENZYMES are protein molecules that help to sped up, or catalyze, a specific reaction.
• The enzyme causes the reactants in a reaction to associate with each other so that they will react to for the products.
Substrate
Enzyme
Active Site
Enzyme-Substrate ComplexProduct
Enzyme
1
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• Reactants in an enzymatic reaction are called SUBSTRATES.
• An enzyme brings substrates together to speed up their reaction.
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• Many enzymes require another non-protein piece to function properly
– APOENZYME: protein portion of the enzyme. It’s shape is what gives it the ability to only run a single type of reaction
– COENZYME/COFACTOR: non-protein portion. The portion that binds to the enzyme and then carries a chemical group or electron of one or both reactants.
• Apoprotein + Coenzyme(s) = Holoenzyme(Haloenzyme)
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Cofactors
• Many enzymes require a cofactor to assist in the reaction. These "assistants" are nonprotein and may be metal ions such as magnesium (Mg++), potassium (K+), and calcium (Ca++).
• The cofactors bind to the enzyme and participate in the reaction by removing electrons, protons , or chemical groups from the substrate.
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Coenzymes• Cofactors that are organic molecules are coenzymes.
• Coenzymes are usually vitamins.
Vitamin Coenzyme NameNiacin NAD+
B2 (riboflavin) FAD
B1 (thiamine) Thiamine pyrophosphate
Pantothenic acid Coenzyme A (CoA)B12 Cobamide coenzymes
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• Coenzymes are cofactors that are not protein. • They bind to the enzyme and also participate in the
reaction by carrying electrons or hydrogen atoms.
Enzyme Enzyme
Coenzyme
Activation Energy
• Many reactions won’t occur unless there is an input of energy added to start the reaction
• This ACTIVATION ENERGY causes the first reactant molecules to collide with enough force to react. They release energy which drives further reactions.
• In the lab this is often achieved by adding heat to increase the number of collisions that occur.
• Activation energy is often shown by the symbol (Ea).
• Enzymes catalyze (speed up) reactions by lowering the activation energy (Ea) required to get the reaction started.
• They do this by bringing the substrates closer together so they are able to react more easily.
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Enzymes Lower Activation EnergyE
nerg
y S
uppl
ied
Ene
rgy
Rel
ease
dActivation energy without enzyme
Activation energywith enzyme
Enzymes lower the amount of activation energy needed for a reaction.
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• Because enzymes are made up of proteins they require a specific substrate at a specific temperature and a specific pH to work properly.
• S.T.E.P.P– S= SUBSTRATE (what substrate does it work on?)– T= TEMPERATURE (at what temp does it work?)– E= ENZYME (what is the name of the enzyme?)– P=pH (at what pH does it work best?– P=PRODUCT (what new chemical products form?)