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?)