[1.7-9] enzymes Flashcards
what is the difference between an anabolic and catabolic reaction?
- anabolic - a reaction which builds things up
- catabolic - a reaction which breaks things down
what are enzymes?
- a globular protein which acts as a biological catalyst
- they lower the activation energy required for a reaction, thereby increasing the rate of reaction, whilst remaining unchanged in the process
why are enzymes important?
- nearly all metabolic reactions in organisms are catalysed by enzymes
- without them, life could not exist
why are enzymes specific?
- each enzyme has a specific amino acid sequence
- which has a particular tertiary structure giving an active site with a unique structure
- shape of active site is complementary to one substrate
how do enzymes lower the activation energy in anabolic reactions?
(if building larger molecules)
- the active site holds monomers closer together and reduces repulsion between them
- this allows them to join/bind together more easily
how do enzymes lower the activation energy in catabolic reactions?
(if breaking larger molecules)
- enzymes bind to substrate in an induced fit, so shape of active site changes
- bond is strained so a lower Ea is needed to break the bonds
what is the lock and key model? (old)
- enzymes have a rigid and set active site shape complementary to the substrate
- substrate = key, enzyme
- substrate will only fit into a rigid active site
what is the induced fit model? (new)
- initially, the enzyme active site and substrate are not complementary in shape
- shape of active site changes as substrate binds / as ESC forms
- shape change stresses the bonds in the substrate causing a reaction
what 5 factors affect enzymes?
- temperature
- pH
- substrate concentration
- enzyme concentration
- non / competitive inhibitors
how do low temperatures affect enzymes?
- lower kinetic energy
- fewer enzyme-substrate collisions
- fewer enzyme-substrate complexes formed
how do high temperatures affect enzymes?
- bonds holding tertiary structure are broken
- active site loses shape and is no longer complementary to substrate
- fewer enzyme-substrate complexes are formed
how does a high or low pH affect enzymes?
- OH- or H+ ions disrupt the ionic and hydrogen bonds holding the tertiary structure together (electrostatic forces of attraction are affected)
- enzyme’s active site loses shape / denatures and is not completely complementary to the substrate
- fewer / no enzyme-substrate complexes formed
how does substrate concentration affect the rate of enzyme activity?
(on a graph)
- start: low substrate conc. not many ES complexes so low rate of reaction
- substrate conc increases, more ES complexes formed, faster rate
- active sites begin to become fully occupied with substrates. rate therefore slows
- active site full with substrate
- maximum rate at which ES complexes can form
- enzyme is the limiting factor
- adding more substrate has no effect
how does enzyme concentration affect the rate of enzyme activity?
(on a graph)
1. enzyme is the limiting factor
- as the conc of enzymes increases, the rate of reaction increases
- this is because more ES complexes form
2. enzyme is the limiting factor
- as the conc of enzymes increases further, the rate of reaction begins to slow down
- this is because we are beginning to not have enough substrate to fill all active sites
3. substrate is the limiting factor
- as conc of enzymes is increased further, the rate of reaction remains constant
- this is because there is not enough substrate to fill active sites
how do competitive inhibitors affect enzymes?
- inhibitor is similar shape to substrate
- inhibitor blocks active site by binding to it
- substrate can’t bind to active site so fewer ES complexes are formed
