topic 1.5 - enzymes Flashcards
what are enzymes
- globular proteins
- act as catalysts to speed up rate of reaction hence reducing activation energy
lock and key model
- active site of an enzyme precisely fits a specific substrate
- it will not bind to any other substrate
induced fit model
- this is when the shape of the enzymes active site and substrate are not exactly complementary
- when the substrate enters the active site a change of shape occurs
stages of induced fit model
- substrate enters active site, forming enzyme-substrate complex
- enzyme changes shape which converts substrate into product/s, forming an enzyme-product complex
- product released from the enzymes active site
effect of temperature on enzyme activity
- if temperature increases too high, enzyme will denature and stop working
- too low temps slow the reaction down
- this is why enzymes have an optimum temp at which they function best
effect of pH on enzyme activity
- each enzyme has optimum pH range
- changing this pH will cause enzyme reactivity to slow down
- if pH decreases too much (becomes too acidic) enzyme denatures
effect of enzyme concentration on enzyme activity
- increasing concentration will speed up the reaction as there is a substrate to bind to
- once all the substrate is bound, the reaction will not speed up
effect of substrate concentration on enzyme activity
- increasing substrate concentration also increases the rate of reaction to a certain point
- once all of the enzymes have bound, any substrate increase will have no effect on the rate of reaction
- available enzymes will be saturated and working at their maximum rate
how is the initial rate of enzyme activity measured
why is measuring initial rate of enzyme activity important
reversible inhibition
when an inhibitor affects an enzyme in a way that does not permanently damage it
competitive inhibition
- competitive inhibitors compete with the substrate for the active site
- inhibitor molecule has a similar shape to the substrate molecule
- when the inhibitor binds it occupies the active site without causing a reaction
how do competitive inhibitors work
- they are similar in shape to the substrate so compete to bind to the active site
- prevents substrate from binding and slows down the rate of reaction for that enzyme
what happens to competitive inhibition when substrate concentration is increased
- increasing substrate concentration can reduce inhibition
- if there is a greater concentration of substrate, the substrate will outcompete the inhibitor for the active site
- so increasing the substrate concentration will increase the rate of reaction (up to a certain point, after which the inhibitor is outnumbered and has a negligible effect)
non- competitive inhibition
- non competitive inhibitors do not bind at the active site
- bind to a different site on the enzyme
what do non-competitive inhibitors do to the shape of the active site
- they change the shape of the active site
- due to this the enzyme can no longer bind to its substrate
what happens to non-competitive inhibition when concentration is increased
- there is no effect
- the inhibitor is binding at a different site so adding more substrate is useless
end product inhibition
- when a final product inhibits an enzyme involved in the initial reactions
how does end product inhibition work
- at the end of a metabolic pathway the final product may inhibit the enzyme responsible for catalysing the initial reaction
- causes the whole metabolic pathway to stop
intracellular reactions
occur inside the cell
extracellular reaction
occur outside the cell
example of intracellular reactions
photosynthesis and respiration
catalase
- intracellular enzyme
- helps break down hydrogen peroxide
examples of extracellular enzymes
digestive enzymes
amylase
- extracellular
- present in saliva
- catalyses breakdown of starch into maltose
trypsin
- extracellular
- present in small intestine
- continues the breakdown of peptide bonds in large protein molecules - starts in the stomach
