BY1: Enzymes

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Enzyme Structure

-Globular proteins that act as biological catalysts.
-They speed up the rate of metabollic reactions.
-Tertiary proteins where the protein chain is folded, with hydrophillic R groups.
-Only a small functional active site.

-These react with the substrate to form an enzyme-substrate complex.
-Only a few amino acids make up the active sites. 

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Properties

-Each enzyme is specific to one substrate molecule, active site only allows one.
-Very fast acting with high turnover rate.
-Enzymes lower activation energy.

-These have to collide with sufficient energy to react.
-"lock and key" analogy, and induced fit model.
-Meaning that the enzyme has a general shape that slightly alters to allow substrate to enter.

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Course Of Enzyme-Controlled Reaction

Shape of the graph:
-When enzyme and substrate are first mixed together, large number of substrate. 
-Both types of molecules are in constant motion. 
-Substrate molecules come into contact with empty active sites.
-All active sites become filled with substrate molecules.
-These convert into product.
-As it progresses, decreases amounts of substrates.
-Graph flattens out, substrate has all been used up. 

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Rate Of Reaction: Temperature

-Graph increases in gradient as there is more kinetic energy, increase in rate.
-Reaction in general doubles in rate every 10 degrees.
-After reaching a temperature of 40 degrees the H bonds break and the active site becomes denatured, thus not being able to react.
-However at low temperatures the reaction stops, but CAN be activated again.

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Rate Of Reaction: pH

-Enzymes have an optimum pH at which they work best at.
-Extremes in pH can denature an enzyme.
-The charges on amino acid chains of the enzyme's active site are affected by H+ and -OH ions, proucing a change in charge.
-Thus the substrate is repelled by the enzyme. 

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Rate Of Reaction: pH

-Enzymes have an optimum pH at which they work best at.
-Extremes in pH can denature an enzyme.
-The charges on amino acid chains of the enzyme's active site are affected by H+ and -OH ions, proucing a change in charge.
-Thus the substrate is repelled by the enzyme.
-At extremes of pH the H bonds are altered.
 

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Rate Of Reaction: Substrate Concentration

-Reaction increase up the point where all active sites are filled, they reach a maximum rate of reaction.

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Rate Of Reaction: Enzyme Concentration

-As long as all other factors are at optimums, the increasing amount of enzyme will increase rate of reaction.

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Inhibition: Competitive

 (E.g. Malonic Acid)

-These have a similar shape to the substrate, and can fit in the active sites.
-This slows the rate of reaction.
-The effects can be reduced with increased substrate concentration. 

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Inhibition: Non-Competitive

 (E.g Cyanide)
-Bind to a different site and alters the overall shape of the protein.
-The active site changes and substrate cannot fit anymore.
-These don't compete for the active sites, but slow rate of reation. 

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Inhibition: Summary


-Competetive inhibitors reach the same point, but more slowly.
-Non-competetive inhibitors have the same rate, but reduced yield.

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Immobilised Enzymes

-Fixed, bound or trapped enzymes in a matrix, such as a gel capsule.
-These can be packed into columns, and substrate passed through them.
-As it is fixed they stay in place and are useful in fermentation as they can be resused.

-They can be used at higher temperatures than normal.
-They can tolerate a wider range of conditions.
-Several enzymes can be used together.
-Can be added or removed, giving better control. 
 

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Biosensors

-An example of immobolised enzymes.
-Great potential in medal diagnostics (e.g. diabetics).
-The electrode probe, with specific enzymes, if enzyme-substrate complexes are formed then a small current is produced; picked up by a transducer.

Steps:
-Blood contains many molecules.
-Enzyme electrode is placed in the sample.
-Glucose diffuses into immobilsed enzyme layer.
-Oxygen is taken up.
-Rate of uptake is proportional to glucose concentration.
-Shows on display the concentration.

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