enzymes

• lock and key model

  -each enzyme is specific to particular substrates

  -active site- complementary to shape of substrate

  -substrate binds to active site to form an enzyme- substrate complex

  -products are released- no longer fits active site
• induced fit model


  -shape of active site doesn't fit shape of substrate exactly

  -active site moulds itself around the substrate

  -close fit needed before reaction can take place

  -enzyme- substrate complex forms

  -products are released- no longer fits active site

  -enzyme reverts back to original shape
• temperature and enzyme activity

  -as temperature increases, rate of reaction increases as there is more kinetic energy- more frequent collisions with more force between the substrate and the enzyme's active site

  -this means more enzyme- substrate complexes form
• extreme temperatures on enzyme activity

  -all enzymes have an optimum depending on their conditions

  -enzymes denature- active site changes shape so it is no longer complementary to the substrate

  -no enzymes- substrate complexes formed

  -kinetic energy breaks the hydrogen bonds in the enzymes tertiary structure- enzymes loses its active site shape
• cold temperatures on enzyme activity

  -enzymes don't denature

  -they become inactive- low kinetic energy so little collisions

  -will work again if heated without denaturing
• temperature coefficient or Q10


  -how much rate of reaction changes when the temperature increases by 10

  -enzyme catalysed reaction where 0-40 has a Q10 value of 2

  -for every 10 increase, rate of reaction doubles

  -when the enzyme denatures, Q10 value drops
• pH on enzyme activity

  -extreme pH denatures an enzyme

  -H-bonds and ionic bonds are broken in the enzymes tertiary structure- broken by H+ and OH- ions

  -attraction to the H+ and OH- ions rather than those involved in the bonds
• substrate concentration


  -more frequent collisions

  -levels off- plateaus

  -all enzymes active site being used- reached vmax

  -no additional effects- ESC forms as fast as possible
• enzyme concentration


  -as soon as substrate leaves. enzymes free to continue catalysing

  -as long as pH and temperature are suitable, rate of reaction is directly proportional to enzyme concentration

  -an enzymes turnover number is the number of substrate molecules that an enzyme can turn into products in one minute

  -turnover number varies considerably between enzymes
• temperature increase- denaturing enzymes


  -ionic and hydrogen bonds holding the enzymes tertiary structure in place are broken

  -peptide bonds remain unaffected

  -active site loses its specificity and can no longer bind to the substrate to catalyse the reaction- no enzyme- substrate complexes form

  -enzyme is irreversibly denatured
• pH on enzyme activity

  -pH is a measure of concentration of H+ ions in a substance

  -H+ ions are attracted to negatively charged ions and molecules

  -interfere with hydrogen and ionic bonds holding the enzyme's tertiary structure by affecting the charges of the amino acid side chains

  -each enzyme has an optimum pH

  -only extremes in pH cause the enzyme to denature
• cofactors


  -any non-protein molecule that must be present that present to ensure that enzyme controlled reactions take place. some enzymes will only work if a cofactor is present
• inorganic cofactors


  -inorganic molecules or ions

  -help form a better fit at the active site for the substrate

  -not changed or used up

  -temporary attachment to the enzyme

  -they don't participate in reaction
• organic cofactors or coenzymes

  -often act as carriers

  -continually recycled

  -many coenzymes synthesised from vitamins

  -participate in reaction- temporarily changed
• prosthetic groups


  -non-protein molecules permanently bonded to the enzyme
• inhibitor


  -enzyme inhibitor is any substance or molecule that slows down the rate of an enzyme- controlled reaction or can stop an enzyme form functioning

  -competitive inhibitors

  -non- competitive inhibitors

  -inhibition can be reversible or non-reversible
• competitive inhibitors


  -competitive inhibitor molecules have a complementary shape to the enzyme's active site

  -bind to active site instead of enzymes normal substrate

  -an enzyme- inhibitor complex is formed but no products are released

  -similar shape to substrate but not the same
• non-competitive inhibitor


  -bind to an area that isnt the active site

  -allosteric area

  -changes shape of active site by interfering with the enzyme's tertiary structure

  -prevents substrate from binding so reaction isn't completed