ENZYMES

ENZYMES

1. ACTION

   • Metabolism - Anabolic and Catabolic reactions
   • Mechanism: Enzymes reduce activation energy needed for the reaction too happen
   • Lock and Key hypothesis: Active site, complimentary to substrate, substrate enzyme complex, enzyme product complex, products released and enzyme is unchanged
     • active site holds substrate in right place so atom groups are close enough to react, r group interactions, temporary bonds which also strain bonds within subtstrate
   • Induced fit: Interaction between enzyme and substrate is weak at first but these interactions induce changes in tertiary structure which strain the molecule which can weaken or strengthen bonds

2. TYPES

   • Intracellular
     • Synthesis of polymers (polysaccharides)
     • Catalase breaks down H2O2
   • Extracellular
     • Nutrients such as proteins and polysaccharides need to be catabolised before entering cells (digestion)
       • This process is carried out by both single celled and multicellular organisms
       • Digestion of starch
         • Initially broken down into maltose by amylase which is found in salivary glands and pancreas (released in small intestine)
           • Maltose is then broken down into glucose by maltase in the small intestine
       • Digestion of proteins
         • Proteins are broken down into peptides by trypsin a protease.
           • Trypsin is produced in the pancreas which is released into the small intestine. The amino acids produced get absorbed into the bloodstream

3. FACTORS AFFECTING ENZYMES

   • Temperature
     • Kinetic energy of molecules increases, increasing the amount of successful collisions
     • Q10(temp coefficient) is a measure of how much the rate of reaction increases with a 10 degree rise in temperature (with enzymes this should double)
     • An increase beyond optimum temperature can denature the enzymes
       • The bonds in the tertiary structure of the active site can break with too much kinetic energy
         • Active site no longer complimentary to substrate
     • Optimum temp: highest rate of activity and varies between enzymes, once denatured above optimum temp the decrease in rate of reaction is rapid
       • Q10 does not apply
     • Extremes
       • Different environments: deep oceans, high altitudes - enzymes in organisms are adapted to the cold with more flexible structures makes them less stable and small temp changes denatures
         • Thermophiles are organisms adapted to hot environments - due to increased bonds in enzymes they are more stable (like H bonds and disulphide bonds)
   • PH
     • H bonds, ionic between r groups holds active site in precise shape
       • Change in PH refers to a change in hydrogen ion concentration (more is low ph, less is high ph)
     • Optimum PH
     • Change in PH: The structure of the enzyme and active site is irreversibly altered - active site no longer complimentary, denatured
       • Hydrogen ions interact with polar and charged R groups, change in H ion concentration changes the degree of this interaction as well as R-R group interactions
       • More H ions (low PH)
         • Less R groups are able to interact, bonds are broken, enzyme changes shape
       • Less H ions (High PH)
         • More R groups interact, bonds are made, enzyme changes shape
   • Concentration
     • Increased substrate particles causes a higher collision rate with active sites + increased rate of reaction
       • Increased enzyme concentration increases active sites available over a particular volume, increasing rate of reaction
     • Vmax
       • All of the active sites are occupied by substrate particles and no more complexes can be formed until products are released
         • Only way to increase rate would be toad more enzyme or increase the temp
     • Limiting factors

4. INHIBITORS

   • Controlling enzyme activity during reaction pathway regulates the rate and quantity of product formation (do not want fast reactions and build up of waste products)
   • Competitive
     • Similar shape as substrate and can fit active site
       • Substate is blocked from entering the active site
         • Enzyme is inhibited
     • Number of substrate molecules binding is reduced
     • Most reversably bind
     • reduces rate of reaction, does not change the Vmax
     • Example: statins, inhibit enzyme of cholesterol synthesis and therefore reducing blood cholesterol concentration
       • Example: aspirin irreversibly inhibits the active site of COX enzymes preventing synthesis of chemical responsible for pain and fever
   • Non competitive
     • Binds to location other than the active site - ALLOSTERIC SITE
     • Tertiary structure of enzyme changes once bound to allosteric site and the active site is no longer complimentary - enzyme is inhibited
     • Increasing Enzyme/substrate conc does not overcome effect of non competitive inhibitor. Increasing conc of inhibitor decreases rate of reaction further
     • Example: Chemicals used in insecticides/herbicides irreversibly inhibit the enzyme needed for nerve impulse transmission which can lead to muscle cramps, paralysis, death
       • Proton pump inhibitors for indigestion irreversibly block the enzyme that secretes hydrogen ions in stomach, this reduces excess acid (which leads to stomach ulcers)
   • end product inhibition
     • when the product of a reaction inhibits the enzyme that produces it - negative feedback control mechanism
     • Excess products are not made and resources are not wasted
     • Non competitive reversable inhibition

5. Cofactors and Prosthetic Groups

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