enzymes

enzymes

1. BIOLOGICAL CATALYSTS THAT LOWER ACTIVATION ENERGY ( the minimum amount of energy needed to activate reaction)

   • allow reactions to take place at lower temperature than normal

2. structure

   • globular 3D protein
   • active site = specific functional region
   • molecule enzyme acts on = substrate
   • substrate fits neatly into active site = enzyme-substrate complex

3. induced fit model

   • active site forms as enzyme and substrate interact.
     • enzyme is flexible and moulds itself around the shape of substrate
       • enzyme has general shape, but alters in presence of substrate
       • as it changes shape, it put strain on substrate
         • strain distorts particular bonds, lowers activation energy needed to break bond
   • any change in enzymes environement = likely to chnage its shape
     • COLLIDING with substrate = change in environement so its shape changed - induced fit

4. lock and key model

   • substrate will only fit in the active site of a particular enzyme
     • specific shape, fits exactly into active site

5. factors affecting enzyme action

   • to work enzymes must 1) come into physical contact with substrate 2) have active site that fits substrate
     • factors that influence rate enzyme works will affect one or both of above
       • as reaction goes on theres less substrate and more product. becomes more difficult for substrate molecules 2 come into contact with enzyme. begins to takes longer for substrate to be broken, and formation of product slows - graphs tail off. graphs flatterns coz all substrate is used up.
   • measuring rate
     • formation of products ie volume produced
     • disappearance of substrate ie reduction in conc of starch
     • change in rate of reaction. gradient y/x. draw triangle
   • TEMPERATURE
     • INCREASE kinetic energy
       • molecules more more quickly, collide more frequent
         • more sucessful enzyme + substrate collisons
           • more enzyme substrate complexes formed
             • rate of reaction increases
     • higher temp than optimum = break H bonds/ other bonds
       • changes shape of active site = enzyme less likely to fit
         • even higher temp, enzyme so disrupted, stops working altogether - DENATURED.
           • falling curve on graph
   • pH
     • change in pH alters charges on amino acids that make up active site
       • substrate cant attach (by bonds) to active site
         • no enzyme substrate complex formed
           • if pH altered a lot, changes tertiary structure ( breaks bonds ) - therefore changes shape of active site
             • H bonds and ionic bond between NH2 and COOH
               • change in H+ ions (pH) affects these bonds
   • enzyme concentration
     • increasing enzyme conc- some of EXCESS substrate can be acted upon.
       • increases rate of reaction
     • if there is no EXCESS substrate (empty active sites), then increasing the enzyme conc will have no impact
   • SUBSTRATE CONCENTRATION
     • if substrate conc is increased, active site gradually become more filled. more molecules to collide with
       • until all of them are working as fast as they can
         • rate of reaction is at its maximum - (V max)
           • addition of more substrate after this = no effect. excess substrate = graph levels off

6. enzyme inhibitors

   • substance that indirectly or directly interferes with functioning of active site of an enzyme - reduce its activity
   • competitive inhibitors
     • molecular shape similar to substrates
       • allows them to occupy active site and compete with substrate for available active sites
         • if substrate conc is increased .. effect of inhibitor reduced
           • eventually all substrate molecules will occupy active sites, higher conc of inhibitor will make this take longer
   • non- competitor inhibitors
     • attach to enzyme at binding site that isnt active site
       • alters shape of enzyme and therefore active site
         • substrate molecules can no longer occupy active site - enzyme cant function
           • substrate and inhibitor not competing for active site- an increase in substrate doesnt reduce effect of inhibitor
     • end product inhibition - keeps a steady conc of a partiular chemical in cell. same chemical often acts as inhibitor of an enzyme at the start of the reaction
       • metabollic pathways - series of reactions, each step is catalysed by an enzyme

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