enzymes Flashcards
what is function of enzymes, how do they do this
reduce activation energy required to form transition state of enzyme substrate complex of reaction
bring substrates together at levels of high proximity, creating high local concentrations, favourable for the formation of the transition state
active site of enzymes contains catalytic groups that interact with substrate, it has complementary shape and charges for substrates
products may have different shapes/charges which repel them from the enzyme
what are main groups of enzymes
oxidoreductase enzymes (catalyse redox reactions)
transferases (enzymes which transfer a group from one substrate to another)
hydrolases (enzymes which hydrolyse bonds)
lyases (enzymes which cleave C-C, C-O, C-N bonds by elimination, thus leavind double bonds)
isomerases (catalyse changes within a single molecule)
ligases(enzymes joining 2 substrates in reaction using ATP or other nucleoside triphosphate)
describe equation between enzyme and substrate
= is a reversible reaction sign
E+S = ES = E +P
where forward rates are k1 and k2 and backwards rates are k-1 and k-2
enzyme kinetics are simplified if k-2 is ignored (which we do), to do this initial velocities are used
what is Vo
the initial rate, before any product has formed, is used since k-2 is not present
only measurements at t=0 show the expected linear rate behaviour
what is initial rate equal to, what is equation for enzyme substrate concentration at equilibira and what is Km
Vo= K2[ES]
at equilibria k1[E][S]= (k-1 + k2)[ES] (rate of formation, left hand side is equal to rate of breakdown, right hand side)
Km = (K-1 + K2)/K1
so at equilibrium:
[ES] = [E][S]/Km
how do experimental factors effect rates at equilibria, what is michaelis menten equation, how is this effected at varying cocentrations of substrate
[E] (free enzyme) = [E]t (total enzyme) - [ES]
[ES] = ([E]t x [S])/ ( [S] + Km)
michaelis menten equation:
Vo= (Vmax x [S]/ [S] + Km), since Vmax occurs when [ES] = [E]t
when [S] is small compared to Km Vo= Vmax x [S]/Km
when [S] is high compared to Km Vo=Vmax
when [S] = Km: Vo= Vmax/2
what is Vmax
max rate acheived by an enzyme, is for a specific concentration of enzyme
what is lineweaver burke plot, describe what it is, associated equations and its function
used to calculate Vmax
1/Vo =
1/Vmax +( (Km/Vmax) X 1/[S] )
a plot of 1/[S] on x axis and 1/Vo on y axis, y axis intercept is 1/Vmax since it represents an infinite amount of S, x axis intercept is -1/Km
also known as double reciprocal plot, line is straight line
what is carbonic anhydrase
carbonic anhydrase accelerates reaction between water and CO2 to form carbonic acid, this enables bicarbonate in blood to be dehydrated to form CO2 as blood passes through lungs
how do concentration of substrates relate to their enzymes in cell often
often concentration of substrate in cell is equal to Km
what is Km value for carbonic anhydrase, what is its turnover rate
Km= 8mM, turnover rate is 600,000/s
what does a small or large Km value indicate about an enzyme
a low Km indicates a tightly bound enzyme substrate complex, a high Km is a weak complex
what is Kcat
the number of substrate molecules converted into product by an enzyme that is fully saturated by substrate (when [S]»_space;» Km)
also equal to the K2 rate
how do Kcat and Km relate to enzyme activity
Kcat/Km measures catalytic efficiency of the enzyme, upper limit of this is between 10^8-10^9 since it is limited by rate of diffusion
high value is highly efficient, since high Kcat is efficient and low Km is efficient
what is rate acceleration, what is the value for carbonic anhydrase
the Kcat value divided by rate constant for reaction in the absence of enzyme (indicating how much the enzyme speeds up reaction)
not easily determined since most cellular reactions occur extremely slowly in absence of enzyme
carbonic anhydrase has rate acceleration of 10^7
