ENZYMES pt2

ENZYMES pt2

1. COFACTORS

   • Prosthetic groups
     • A cofactor that is PERMANENTLY bound, by covalent bonds, to an enzyme molecule
       • v [E.G] v
         • The enzyme Carbonic Anhydrase contains zinc ion permanently bound to its ACTIVE SITE => this enzyme is found in red blood cells & catalyses the interconversion of CO2 & H2O to carbonic acid
   • Other (TEMPORARY) cofactors
     • some enzymes work better in the presence of ions that aren't permanently bound to them ->these ions are also cofactors
       • Enzyme & substrate molecules TEMPORARILY bind together to form an enzyme- substrate complex. ->presence of certain ions that temporarily bind to either the substrate (co-substrate) or enzyme (co-enzyme) may ease the formation of ES complexes & therefore increase the rate of enzyme-catalysed reactions
         • Coenzymes
           • ~coenzymes are small organic non- protein moles that bind temporarily to the active site or enzyme molecule ->either just before/ at same time the substrate binds ->coenzymes are chemically changed during the reaction, & they need to be recycled to their original state (sometimes by diff enzyme)
           • Some vitamins are sources of coenzymes
             • ~many coenzymes are derived from water- soluble vitamins ->if these vitamins are deficient in the diet of humans, then certain diseases may result.
         • Cosubstrates
           • *some cofactors act as co-substates ->they & the substrate join together to form the correct shape to bind to the active site of the enzyme
             • *some cofactors change the charge distribution on the surface of the substrate molecule or on the surface of the enzyme's active site, & make the temporary bonds in the enzyme- substrate complex easier to form
               • > [E.G] >
                 • ~the enzyme amylase digests starch to maltose, & will only function if chloride ions are present

2. INHIBITORS

   • They are substances that reduce the activity of an enzyme by combining with the enzyme molecule to alter how the substrate binds
     • Inhibitors are reversible or irreversible , covalent bonds mean it is irreversible and weak hydrogen bonds mean its reversible
   • COMPETITIVE
     • Competitive inhibitors have a similar shape to the substrate
       • This means they can occupy the active site to form enzyme inhibitor complexes, essentially blocking the active site off for the substrate
         • substrate molecule cannot enter so the rate of reaction slows down; The inhibitor + substrate are COMPETING for an enzymes AS -> level of inhibition is dependent on the CONCENTRATION OF SUBSTRATE & INHIBITOR MOLECULES
   • NON-COMPETITIVE
     • Do not compete with substrates, instead binds to the enzymes ALLOSTERIC SITE
       • This disrupts the enzyme's tertiary structure which changes the active sites shape, meaning the substrate can no longer bind
         • ES complexes are prevented and so the rate of reaction is decreased. Since they do not compete w/ substrates, they are not affected by SUBSTRATE CONCENTRATION
   • OTHER INHIBITION METHODS
     • METABOLIC PATHWAY CONTROL
       • [!] The product of one enzyme-catalysed reaction becomes the substrate for the next enzyme in the metabolic pathway
         • The final product in the MP becomes the NON-COMP inhibitor for an earlier enzyme in the MP, binding to its allosteric site to REGULATE THE MP
           • Organelles have this take place in an enclosed area = decreases diffusion distance for products to move onto next enzyme = decreases overall time taken
       • < [E.G] <
     • END PRODUCT INHIBITION
       • After the ES reaction's completion, the PRODUCT MOLECULE stays tightly bound to the enzyme due to the NEGATIVE FEEDBACK
         • the enzyme now CANNOT form more product than the cell needs
   • POISONS & DRUGS
     • [DRUG] They work by inhibiting enzymes too; (e.g) ACE (angiotensin - converting enzymes) works in the MPW and it increases blood pressure. To lower it, an ACE inhibitor drug must be used
       • ACE inhibitor uses -> lowers blood pressure -> treats heart failure & reduces heart attack + strokes risks. ASPIRIN reduces blood clot risks by competitive inhibition
     • [POISON] CYANIDE inhibits aerobic respiration, it is hydrolysed to produce HYDROGEN CYANIDE; toxic gas which splits into H+ & CN- ions.
       • CN- ions bind IRREVERSIBLY to an enzyme in mitochodira, which inhibits the final stage of aerobic respiration
         • blood flow to tissues increases because of lack of oxygen

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