Enzymes Flashcards
what is an enzyme ?
a biological catalyst which increase the rate of a chemical reaction by lowering the activation energy of the reactions they catalyse
structure of an enzyme
globular protein it has a tertiary structure
- helix folds back on itself, giving the molecule a unique 3D shape - hydrogen, disulphide + ionic bonds
- active site is formed
what are the two types of reactions when they catalyse ?
anabolic reaction
catabolic reaction
anabolic reaction
larger molecules are built from smaller molecules
catabolic reaction
larger molecules are broken down
what is the active site ?
the area of the enzyme where the substrate binds
as the enzyme and substrate binds what forms ?
an unstable enzyme - substrate complex, which breaks down to form products
Induced fit model
- enzyme actually changes shape as the substrate binds to its active site
- active site does not correspond exactly to the shape of the substrate
- the active site has a more flexible shape + able to mould around the shape of the substrate
activation energy
the amount of energy needed to raise the substrate molecules to their transition state
state the 4 factors which affect the rate of enzyme-controlled reactions
- temperature
- pH
- substrate concentration
- enzyme concentration
Temperature
- low temp = low rate
- enzyme have too little kinetic energy and move slowly
- few successful collisions between enzyme and substrate leads to low rate of reaction - optimum temp = high rate
- enzymes have a lot of kinetic energy and move quickly
- lots of successful collisions between enzyme and substrate leads to high rate of reaction - high temp = denatured = low rate
- heat breaks the bonds maintaining the tertiary structure of the enzyme
- the active site becomes denatured and substrate no longer fits
- no successful collisions leads to a low rate of reaction
pH
- low optimum = low rate
- pH has this effect because the structure of the protein is maintained by bonds in the tertiary structure
- a change in pH alters the bonding and the shape of active site changes thus the substrate can no longer bond - optimum pH = high rate
- active site has the appropriate shape to bind with the substrate so the reaction is catalysed the fastest - pH above optimum = low rate
Substrate concentration
- low substrate concentration = low rate
- few substrate molecules limits chance of successful collisions between enzyme + substrate - high substrate concentration = high rate
- more substrate molecules increase the chance of successful collisions between enzyme + substrate
what are the two phases of substrate concentration ?
- lower substrate concentration = rate increases in proportion to the increase in substrate concentration
- higher substrate concentration = rate of reaction becomes constant, the rate will not increase even though the substrate concentration is still increasing
Substrate concentration - low
there is an excess of enzyme molecules, lots of free enzyme molecules
substrate concentration = limiting factor
Substrate concentration - high
there becomes a point where the concentration of substrate is higher than the concentration of enzyme molecules - no longer free enzymes molecules that can react
enzyme concentration = limiting factor
what do the substrate molecules have to do to react? - substrate conc high
queue up
what happens when adding more substrate molecules? - substrate conc high
only increases the number that are waiting - DOES NOT INCREASE RATE
Enzyme concentration
- low enzyme concentration = low rate
- few enzyme molecules limits the chance of successful collisions between enzyme and substrate
- excess of substrate with no free enzymes - high enzyme concentration = high rate
- more substrate molecules increase the chance successful collisions between enzyme and substrate
inhibitors
substances which stop the enzyme from binding to its substrate, therefore controlling the progress of a reaction
what are two types of inhibition ?
- competitive
- non-competitive
Competitive inhibition
an inhibitor molecules compete with the substrate for binding to the active site of the enzyme, therefore preventing the substrate from binding
- can be reversed by increasing the substrate concentration
Non-competitive inhibition
an inhibitor doesn’t bind to the active site but binds to a different part of the enzyme and changes the shape of the enzyme
- decreases the reaction as the active site does not fit the substrate and the substrate cannot bind to the enzyme
- cannot be reversed by increasing substrate concentration
what happens if the concentration of substrate molecules is high enough ? - competitive inhibitor
it will displace the inhibitor from the active site - less likely the inhibitor will bind
when adding more substrate it does not dislodge why? - non competitive inhibitor
they are not competition for the enzymes active site - permanent
what is end product inhibition ?
the final product often acts as a regulator of the pathway in a process
process of end-product inhibition
- when the amount of end product is high, it binds non competitively to an enzyme in the pathway, blocking further production itself
- regulation of a metabolic pathway by negative feedback
- when the amount of end product falls, inhibition ends and the pathway restarts
