enzymes Flashcards
what are enzymes and what do they do
enzymes are biological catalysts that speed up the rate if reactions by lowering the eA and are chemically unaltered at the end of the reaction and thus are reusable and effective in small amts
they are also globular proteins with an active site with specific 3D conform that is complementary in shape and charge to a specific substrate
soluble in water as they are globular proteins with hydrophilic aas on the external surface and vice versa
explain lock and key hypothesis
the enzyme AS has a conformation tht is complementary in shape and charge to a specific substrate ; when enzymes and substrate molecules collide in the correct orientation an ES complex forms; catalysis occurs and products formed no longer fit the AS and leave, making the AS available once again
explain induced fit hypothesis
binding of the substrate to the enzyme AS induces a conformational change in the AS of the enzyme such that it now provides a more precise fit for the substrate, making it more effective.
what are the 3 important types aa residues that help the enzyme function
contact residues: found in the AS and helps to position the substrate in the correct orientation via weak interactions such as HB IB and HI.
catalytic residues : found in the AS and have specific r groups that act on bonds in the substrate and help to catalyse the conversion of substrate to product
structural residues: maintain overall 3D conformation
what are enzyme cofactors (3 types)
inorganic ions (e.g mg2+ in PCR)
prosthetic groups: haem cgroup of cytochrom oxidase
coenzymes (e.g NAD)
how do enzymes speed up metabolic reactions? (3 effects)
proximity effects : temporary binding of substrates in close proximity increase chance of a reaction
orientation effects: held in an orientation that enable the bonds in substrates to be exposed to chemical attack
strain effects: slight distortion of substrates when they bind to the enzyme AS, strains bonds in substrates that need to be broken
how do people measure rate of reaction
measure product formed per unit time duh
effect of substrate conc
as substrate conc increases the freq of effective collisions increases, rate of ES complex formation increases and ROR increases as AS of enzymes are readily avail and Substrate conc is limited; once the AS are saturated and substrate conc is no longer limiting, graph plateaus as Enzyme conc is now limiting
effect of temp on enzyme
as temp increases, KE of enzyme and substrate molecules increases, frequency of effective collisions between enzyme and substrate molecules increases; rate of ES complex formation increases; number of substrate molecules with sufficient energy to overcome eA and form products increases, rate of reaction increases until optimum temp is reached where ROR peaks.
for every 10degc increase in temp, rate of reaction doubles.
beyond the optimum temp, KE continues to increase, intramolecular vibrations increase, HB IB and HI between R groups that maintain the 3D config are disrupted; enzyme denatures and specific conform is lost, substrate is no longer complementary to the shape and charge of AS and thus rate of ES complex formation decreases and ROR decreases
effect of Ph on enzyme
at optimum pH the conformation of the enzyme is the most ideal for substrate binding and ROR is the highest. as ph deviates from the optimum, excess H+ or OH- ions affect the ionisation fo the R-groups of the aa residues, thus ionic bonds and HB that maintain the conformation of the enzyme active site is disrupted and the enzyme denatures
thus the rate of ES complex formation decreases and ROR decreases
effect of enzyme conc
as enzyme conc increases, the freq of effective collisions increases; rate of ES complex formation increases and ROR increases
at the plataue enzyme conc is no longer the limited factor
what is allosteric inhibition/activation and how does it work
binds to an allosteric site
made of a multimeric enzyme with multiple AS and allosteric sites
inhibitor binds to allosteric site that results in conformational change in the enzyme, stabilising the enzyme into an active or inactive state
substrate binding stabilises the enzyme in the active conformation and opposes the effect of the inhibitior, allowing V man to be achieved at high substrate conc. (they exhibit cooperativity and hence have a sigmoidal ROR graph )
what is michaelis constant (Km)
the substrate conc at which the reaction proceeds at half its max rate
high = low affinity and vice versa
what is competitive inhibition and how does it work
binds to AS
inhibitor competes with substrate for AS and reduces availability of AS for substrate binding, decreasing ROR
at high substrate conc, effect of inhibitor is negligible as the higher proportion of substrate molecules effectively outcompete the inhibitor molecules for the active site. thus the effects of inhibition can be overcome and Vmax can be reached at a high substrate conc
what is non-competitive inhibition and how does it work
binds to an alternative site
results in a conformational change in the enzyme AS thus decreases ROR
cannot be overcome by increasing substrate conc
