12 and 13 Enzymes and their mechanisms Flashcards
What does a catalyst do?
A catalyst reduces the activation energy (Ea), also called the free energy of activation (ΔGdagger). The catalyst provides an alternate route of reaction and can put reactants in the correct orientation, the catalyst is not changed in the reaction.
What are two ways for improving the likelihood that a reaction will proceed?
Increasing the temperature, pressure and using a metal catalyst. These things either add energy or put material in the correct orientation.
Why do living systems use catalysts? Why do they then use enzymes for catalysts?
Living systems use catalysts because raising the temperature may damage structures. They use enzymes because many free metals are harmful to the organism. Also enzymes are very specific for their substrate.
How much can a enzyme increase a reaction rate?
Up to 10^7 to 10^19
What is free energy of activation?
The amount of energy to convert 1 mol of substrate (reactant) from the ground state to the transition state
What is the active site of an enzyme?
A site on an enzyme that binds the substrate. it has amino acid side chains that actively catalyze and it can optimally orient the substrate to achieve the transition state at a lower energy.
What are the two models of enzyme binding to substrate?
Lock and key
Induced fit
What are two non-protein components that often allow enzymes to function?
Cofactors (ions)
Coenzymes (complex organic molecules)
Coenzymes facilitate the binding of substrate to enzyme
What are holoenzymes?
Intact functional enzymes with cofactors (prosthetic groups)
What is a enzyme called which has only its protein component (no cofactor/prosthetic groups)?
Apoenzyme
What is the lock and key model of enzyme-substrate binding?
Proposed by Emil Fischer, each enzyme binds toa single type of substrate because the active site and the substrate have complementary structures. Shape and charge distribution allows interaction.
What is the induced fit model of enzyme-substrate binding?
Flexible structure of protein taken into account, substrate does not fit precisely at first. Non-covalent interactions between the enzyme and substrate causes a conformation change in the enzyme that llows the active site to change its shape to that of substrate.
Do enzymes bind to many substrates?
No, there are only a few known samples where an enzyme moonlights for another substrate.
What are the six major categories of enzymes?
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- ligases
What is the rate/velocity of a reaction
The change of a concentration of reactant or product per unit time
What is initial velocity (Vo)?
The velocity at the beginning of a reaction when the concentration of substrate greatly exceeds enzyme concentration
What are enzyme kinetics?
Information about rates, the quatitative study of enzyme catalysis as well as the enzyme affinity for substrates and inhibitors
What are first order reactions? What is the rate equation?
Determined experimentally. A unimolecular reaction (no collision is required). The rate equation is rate=k[A]
What is half life
The time for one-half of the reactant molecules to be consumed
What are second order reactions and their rate equation?
Bimolecular reactions with two substrates (eg. A+B = P).
Rate=k[A][B]
What is a zero order reaction?
The rate is not affected by adding more substrate, enzyme active sites are saturated. It is the point on a reaction coordinate graph where the line flattens out horizontally
What is the concept of enzyme-substrate complexes and who developed it? What is the equation and the three contants?
Michaelis-Menten kinetics explains the formation and dissociation of the Enzyme-Substrate Complex (ES). It goes like this:
E + S ⇌ ES -> E + P
E - Enzyme
S - Substrate
ES - Enzyme-substrate complex
P - Product
There are three rate constants for this formation and dissociation.
k1 - Rate constant for ES formation (E + S -> ES)
k-1 - Rate constant for ES dissociation (ES ⇌ ES E + S)
k2 - Rate constant for product formation and release from the active site (ES -> E + P)
What is the equation for the rate of formation of ES
Rate of formation of ES = k1[E][S]
What is the equation for the rate of ES dissociation?
Rate of ES dissociation = (k-1 + k2)[ES]
What is the steady state assumption?
The steady state assumption states that the rate of formation of ES is the same as its dissociation
What is the Michaelis constant (Km)
The lower Michaelis constant, the greater the affinity of the enzyme for its substrate
Vmax is?
Vmax is the maximum velocity that a reaction can attain
What is kcat k(cat) (catalyst constant) and what is the equation for it?
The catalytic constant is the number of substrate molecules converted to product per unit time. Kcat=(Vmax)/[Et]
[Et] = total enzyme concentration
It can also be thought of as the maximum capacity for a particular enzyme or the turnover number