Enzyme Kinetics Flashcards
Why is the rate of biological reactions important?
Most cellular chemicals thermodynamically unstable, rely on rate of breakdown being too slow
System to make reactions physiologically different
Diseases caused by imbalances in rates at which reactions are taking place
What are free energy changes?
Delta G
depends on free energy of products minus free energy of reactants
provides no information about rate of reaction
rate of reaction depends on free energy of activation
What is activation energy?
energy that a molecule is required to overcome the transition state free energy barrier
only certain proportion of molecules in a mixture will have the required energy
defines ror at particular case
what is the Arrhenius equation?
k = Ae-(Ae/RT)
R= rate constant
T= absolute temp (K)
A= constant that defines rate
AE = activation energy (J)
R= universal gas constant
Hoe do you increase the speed of a chemical reaction?
Increase temperature
Increase pressure
Change the pH
General properties of enzymes
Catalytic- ends in state that is started
Specific- change rate of limited set of reactions
Fast- most reactions need to be sped up
Why are enzymes proteins?
can be specific (20 aa)
aa have very different chemical properties, speed
accommodate different reactants, protein not changed in reaction
How is the transistion state barrier reduced?
Enzymes decrease activation energy
stabilise the unfavourable intermediate
- charge-charge interactions
- hydrogen bonding
- protecting hydrophobic groups
make possible a less favourable reaction
- provide acid/base like conditions
- allow oxidation/reduction
- provide small vacuum
- provide an attacking group (covalent catalysis)
- provide a metal ion
No enzyme
rate of an elementary reaction proportional to frequency with which the reacting molecules come together
proportinality known as rate constant R
No enzyme: S -> P
Enzyme: E+S -> ES -> EP -> E+P
Assumptions of enzyme kinetics
release of product is very fast
reverse reaction is sufficiently slow so can ignore
Michaelis-menten equation
Most enzyme obey Michalis-Menten kinetics bust some do not
Vo = Vmax [S] / Km + [S]
Vo = reaction velocity
Vmax = maximal rate
[S] = substrate concentration
Km = Michaelis contstant
Km important characteristics?
values range widely
lie mainly between 10-1 and 10-7M
depends on substrate & conditions
What is Km?
concentration of substrate at which half the active sites are filled
provides measure of substrate concentration required for significant catalysis to occur
provides approximation of substrate conc in vivo
measurement of substrate concentration
measurement of binding in the enzyme substrate conc
Km is measure of strength of ES complex
High Km:
Indicates weak binding
needs lots of substrate to fill active sites
Low Km:
Indicates strong binding
Needs a little amount of substrate to fill active sites
Indicates affinity of ES complex only when K-1 is much greater than K1
Vmax reveals turnover number, also called Kcat
- how quick reaction turning over
How to calculate michaelis-menten constant
- Must obtain value for Vo for at lear 5 values of [S]
- values of [S] should be both sides of Km for a good result
- constants for the enzyme can then be calculated
- need to record initial reaction velocity at no different [S]
