Enzymes 3.1.4.2

• What is an enzyme?

  Enzymes are biological catalysts that lower activation energy but is not used up/changed during a reaction. Protein
• lock and key model


  The model of the enzyme that shows the substrate fitting perfectly into the active site

  
• Why will each enzyme only catalyse one specific reaction?

  Because each enzyme has a specific 3D tertiary structure, resulting in its active site having a specific shape, so only complementary substrates can bind to it, forming an enzyme-substrate complex
• The induced fit model


  1) before reaction, active site is not complementary2)as substrate binds, active site changes shape to form an enzyme-substrate complex3)this stresses and distorts the bonds in the substrate, causing the reaction to occur and the products to be released
• What does an enzyme require to catalyse a reaction?

  -come into contact with a substrate -substrate must be completely complementary to active site -must collide with efficient energy-must collide at correct orientation
• exergonic and endergonic reactions

  
• Factors which affect the rate of enzyme controlled reactions

  -temperature-ph-enzyme concentration -substrate concentration
• Temperature (exam mark scheme)

  1) as temperature increases, rate of reaction increases 2)due to increased kinetic energy of enzyme and substrate molecules3)above optimal temperature, rate of reaction decreases4)because enzyme denatures due to increased kinetic energy5)breaks hydrogen/ionic bonds between amino acids6)changes shape of active site so less E-S complexes formed
• PH


  Different enzymes have different optimal PHs-above or below optimal PH, the enzyme denatures as it causes the bonds to be broken, the shape of the active site changes due to change in the 3D tertiary structure and can no longer form enzyme substrate complexes as no longer complementary
• What is an enzyme inhibitor?

  Reduce binding of enzyme or substrate to prevent formation of enzyme substrate complexes
• Competitive inhibition


  1)inhibitor is similar to substrate 2)so the inhibitor fits/binds to active site3)this prevents/reduces E-S complex forming4)can be overcome by increasing substrate concentration
• non-competitive inhibition


  1)inhibitor attaches to enzyme at the allosteric site2)this changes the shape of the active site3)so active site and substrate are no longer complementary so no E-S complexes formed4)cannot be overcome
• Rate of reaction with inhibitors

  
• purpose of inhibitors


  Helps regulate production of certain products (cells don't want to make more product than required, so negative feedback is used to speed up/slow down /stop enzymes to control the metabolic pathway based on cell demands)
• Feedback inhibition with metabolic pathways

  Sequence of chemical reactions which occur in a specific order as the product of one reaction is the substrate for another and often the end product is used as an inhibitor for the original reaction
• Describing a product time graph