Enzymes Flashcards
What is an enzyme?
biological catalyst which speeds up the rate of reaction by providing an alternative pathway of lower activation energy
Description of enzymes
never get used up
globular protein
has an active site which is complementary to the substrate it binds to, to form an enzyme-substrate complex
can be intracellular or extracellular
What is an intracellular enzyme?
inside the organism
What is an extracellular enzyme?
outside the organism
What is the active site of an enzyme determined by?
the primary structure
What is the primary structure?
a long chain of amino acids in which the order and sequence is key to the R groups and the bonding between them causes the chain to fold into 2D and 3D structures
What is the lock and key hyphothesis?
active site is already perfect shape for substrate to fit
perfect fit
What is the induced fit hypothesis?
active site changes shape to fit substrate
not perfect fit
describe the induced fit hypothesis
active site is complementary, but not a perfect fit
induces conformational change (active site changes shape)
puts strain on bonds on active site which lowers the activation energy
reaction occurs and products released from active site
How does temperature affect enzymes up to the optimum?
increase in temp, increase KE
causes more frequent collisions
more enzyme substrate complexes will be formed
more products
so increase in RoR
How does temperature affect enzymes past the optimum
KE becomes too high
collisions are too violent
hydrogen bonds and london forced between R groups which hold 3D structure are broken
causes the active site to change shape
the active site is no longer complementary to substrate
active site of enzyme becomes denatured
less enzyme-substrate complexes formed
RoE decreases
How does pH affect enzymes at optimum
optimum pH varies between enzymes
at optimum, active site is complementary to substrate shape and charge
How does change in pH affect enzymes
away from optimum causes RoR to decrease
ionic forced and hydrogen bonds get disrupted
causes a change in 3D and tertiary structure
active site changes shape and is no longer complementary to substrate
less enzyme-substrate complexes formed
slight changes in pH changes bonding but its reversible
extreme pH denatures enzyme permanentely
How does enzyme concentration affect enzymes
increase means more active sites are available
more collisions so more enzyme-substrate complexes formed
at high enzyme concentration, concentration of substrates becomes limiting factor
further increase of enzyme concentration will have no effect as empty active sites
How does substrate concentration affect enzymes
increase means increase in frequency of correct collisions
until all active sites are occupied
then further increase in substrate concentration has no effect - not limiting factor
What is a competitive inhibitor?
inhibitor molecule is a similar shape to substrate and therefore complementary to active site
How does competitive inhibitor reduce reaction
Blocks substrate molecule so it cannot enter
forms an enzyme-inhibitor complex
reduces the number of active sites available for substrate
binding is reversible
what does the amount of inhibition depend on in competitive inhibitors?
relative concentration of substrate and inhibitor molecules
more inhibitors collide with active sites so effect of inhibition is greater
What is a non-competitive inhibitor
inhibitor molecules don’t bind to active site
aren’t complementary with substrate molecules
How do non-competitive inhibitors reduce rate
bind to a second part of enzyme (allosteric site)
changes 3D tertiary structure of enzyme
changes shape of active site
substrate can’t bind
fewer enzyme-substrate complexes formed
Why does substrate concentration not effect non-competitive inhibitors
any enzyme molecule which has an inhibitor bound to it cannot catalyse a reaction
What are activators
some molecules are activators, changing shape of active site to its active form
What is end product inhibition?
end product acts as non-competitive inhibitor
product binds to allosteric site of first enzyme\causes change in 3D tertiary shape of enzyme and active site shape
pathway shuts down
How is end product inhibition reversed?
when concentration of product falls, final product detaches from allosteric site, enzyme returns to original shape allowing pathway to resume
