Enzymes Within the Cell

What are enzymes?

An enzyme is a protein molecule that is a biological catalyst. An enzyme has three traits:

• Enzymes increase the speed of a reaction, 
• Enzymes react with only one reactant (a substrate) to produce the final product,
• And enzymes are regulated from low activity to high. 

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Enzymes increase the reaction rate without changing the chemical makeup of a reaction. Most information about enzymes has been discovered due to the extraction and isolation of enzymes from cells and are put to work in test tubes. There are around 3,000 enzymes within each individual cell. If one enzyme were to be defective or missing, it can be disastrous. 

Parts of an Enzyme

• Apoenzymes are the protein parts of an enzyme. Apoenzymes in its inactive form is called a proenzyme and contains amino acids to complete the final tertiary structure to be formed. 
  
• Cofactors are a non organic protein substance. They are to either activate the protein or to be involved in the reaction.

The bond between aponenzymes and cofactors in some cases may be loose and connected only during a reaction while in other cases, they may be held together by covalent bonds

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Enzyme Nomenclature

Enzymes are generally named in correlation to the substrate molecule it is reacting with. They end in -ases to the root name of the molecule. A few enzymes such as pepsin, trypsin, and chymotrypsin, which catalyze the hydrolysis or proteins, were named before the naming system was created. 

Type of Enzyme

Oxidases/Dehydrogenases
Transferases
Hydrolases
Lyases
Isomerases
Ligases/Synthetases

Reaction

Oxidation-reduction
Functional group transfer
Hydrolysis 
Addition to double bonds (or reverse)
Isomerization
Formation of bonds with ATP cleavage 

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How Enzymes Work

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Enzymes bind to their substrate with an active site. An active site is a cleft or groove on the surface of an enzyme made up of amino acids. Inside the active site is where the enzymatic catalysts occurs. The substrate binds to the active site in a variation of bonds, such as hydrogen bonds, ionic bonds or hydrophobic interactions.  Each enzyme-substrate interactions are different and specific to the pair. Therefore, only the correct substrate can bind to with the enzyme.
Once the substrate has bonded to the enzyme, the reaction takes place. The reaction may be determined by the nature of the enzyme. An enzyme may "couple two different reactions". This means that with an endothermic one, it can allow the enzyme to drive the endothermic reaction by using the energy given off by the exothermic reaction. In this process, ATP is the fuel that powers the required energy in living organisms. 
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