enzymes

• what is an enzyme: they are biological catalyst, they speed up the rate of chemical reaction that occur in the organisms
• anabolic reactions: making large molecules from small ones
• catabolic reactions : breaking down large molecules
• what are all the reactions that occur in an organism called: metabolic reactions
• intracellular enzymes: enzymes catalysing metabolic reaction within cells- in normally in their organelles
• extracellular enzymes:

  • released by a cell into its surroundings
  • eg digestive enzymes
• what is the structure of enzymes:

  • made from globular proteins
  • these are folded so that their tertiary structures form an active site which is complementary to the shape of a specific chemical (substrate)
  • combine to form a enzyme -substrate complex
• what are the 2 hypothesis:

  • lock and key
  • induced fit
• lock and key hypothesis:

  • substate fits into specific active site with  complex shape
  • enzyme-substarte formed
  • reaction occurs
  • product leaves active site
• induced fit hypothesis:

  • different form lock and key hypothesis as it suggets that it is rigid and its fixed
  • but when substrate enters the active site it is induced, changes shape
• what are the factors that effect enzyme activity:

  • temperature
  • pH
  • concentration effects of changing substate []
• temperatures:

  • all molecules have kinetic energy which allows them to move randomly and collide with each other from time to time
  • increasing temp increaes kinetic energy , therefore increases the chance of collision occuring
• enzymes and temp:

  • increases the number of successful collisions between substrate and active site
• too hot:

  • as temp increases above the optimum the molecule making up the energy gain kinetic energy and begin to vibrate more
  • vibrations cause ionic and hydrogen bonds to break irreversibly changing the 3D shape of AS so substate can no longer fit
  • enzyme has denatured
• pH:

  • Ph indicates the number of H ions present
  • high H+ = low pH acidic
• enzyme structure and pH:

  • H bonds and ionic forces hold the teritary structure together , determines the shape of the active site
  • increaseing or decreasing the number of H + present can interfere with these bonds and cause active site to change shape
  • small changes in the pH can cause temporary change in the H bonds and therefore shape denatures but can be reversed by returning to the optimum pH
• summary : temp:

  • increasing temp, increases kinetic energy, increases vibrations - H bonds break and enzyme is denatured
• summary changing pH:

  • hydrogen bonds break, enzyme denatured maybe renatured
• effects of changing enzyme []:

  • increasing enzyme [] increases the nummber of AS present therefore more successful collisionsbetween AS and susbstrate molecules will occur
  • more AS - sub complexes will form and therefore the rate of reaction will increase
• what are the limiting factors for the effects of changing enzyme []:

  • substrate [] and temp
• enzyme inhibitors:

  • inhibitors are substances which slow down enzyme  activity
• what are the 2 types of inhibitors:

  • competitive and non-competitive
• competitive inhibitors:

  • chemicals that have a shape that is similar to that of the substate, means it will fit into the AS of enzyme and block it
• what do competitive inhibitors reduce:

  • reduce the number of free active site and therefore fewer E-S complexes form and rate of reaction decreases
• the effect of most competitive inhibitors are reversible how?:

  • can be reduced by increasing substrate []
• inhibitors that bind irreversibly are called:

  • inactivators
• non-competitive inhibitors:

  • these are chemicals that bind to regions of the enzyme known as the allosteric site
  • this binding cause the shape of the AS to chnage so it no longer is complememtary to it susbstrate
• increasing the sub /enzyme [] has no effect on/.... :

  • non-competitive inhibitors
• end product inhibition:

  • this occurs when end product acts as an inhibitor and stays bound to the allosteric site of the enzyme that produces it
  • this is an example of negative feedback and prevents too much of a product being produced
• co-factors:

  • are non-protein substances that are needed for an enzyme to function correctly
  • ions that are not permantly bound to the enzyme eg Cl- is a cofactor of amylase helping to form its active site 
  • can alter the charge of molecules to ensure the ES complex forms correctly
• co-enzyme:

  • they are organic , that bind together with the active site to ensure substrates fits and binds correctly
  • have to be recycled
• prosthetic group:

  • they are part of the structure of an enzyme they are known as prosthetic group
  • iron or zinc 
  • eg zinc is permanently bound to the enzyme carbonic anhydrase found in red blood calls and is essential for the carriage of CO2 in mammals
• enzyme inhibitions

  • cyanide is highly toxic because it inhibits aerobic respiration
• temperature coefficient

  Q10 = rate of reaction (T.c + 10 )/ rate of reaction T .c
• snake venom

  • venom of a green mamba snake contains a chemical that inhibits the enzyme ACh , important of the neuromuscular synapses to break down acetylcholine, if this enzyme is inhibited it is attached to the receptors on the muscle membrane and keeps the muscle contracted = causes paralyses