Enzymes

what do enzymes do ?

catalyse reactions by lowering the activation energy required for a reaction to occur by providing an alternative reaction pathway.

what kind of protein is an enzyme ?

globular

why is the tertiary structure of an enzyme important ?

• the tertiary structure must be maintained so the substrate can fit into the active site

• mutations in primary structure can affect the tertiary structure

what happens when an enzyme meets a substrate ?

the substrate fits into the active site to form a enzyme-substrate complex

what kind of reactions do enzymes catalyse?

metabolic

what kind of metabolic reactions are there?

catabolic (breaking substrates down into smaller molecules) and anabolic (building up smaller molecules into a larger molecule)

what is an intracellular enzyme ?

remains active within the cell

what is an extracellular enzyme ?

secreted from a cell to be active

what is the lock & key model ?

• when substrate is complementary to the active site

• so temporary bonds form between active site and substrate (lowering the activation energy)

• when it fits, the products are formed and they are released

what is the induced fit model ?

• substrate is not complementary to the active site

• so the active site moulds itself around the substrate

• temporary bonds form between active site and substrate (which are weakened, lowering the activation energy)

• once products are formed, the active site returns to it’s original shape

what factors affect enzyme activity ?

pH, temperature, enzyme concentration, substrate concentration

how does pH affect enzyme activity?

• as pH becomes more alkaline, more OH- ions are present which react with positive R groups in the enzyme.

  • this alters the ionic bonds in the tertiary structure, altering shape of the active site and denaturing the enzyme !

  • (same goes for acidic pH as H+ ions react with negative R groups)

how does temperature affect enzyme activity?

• as temperature increases, rate of reaction increases

  • as molecules gain kinetic energy so more successful collisions occur

  • however, after a certain point, bonds in the tertiary structure break due to the temperature - denaturing the enzyme.

how does substrate concentration affect enzyme activity?

• as substrate concentration increases, rate of reaction increases

  • increased rate of successful collisions between active site + substrates

  • forming enzyme-substrate complexes and more products formed within a given time

• however, it plateaus at a certain point as the concentration of enzymes become a limiting factor (not enough enzymes to react with substrates) → this is it’s V-MAX

how does enzyme concentration affect enzyme activity?

• as enzyme concentration increases, rate of reaction increases

  • increased rate of successful collisions between active site + substrates

  • forming enzyme-substrate complexes and more products formed within a given time

• however, it plateaus at a certain point as the concentration of substrates become a limiting factor (not enough substrates to react with enzymes)