SFP6+7 - Enzymes Flashcards
What is the equation to determine the reaction rate of a reaction?
∆R/P / ∆t (change in reactants or products over time)
What tends to be the unit to measure the rate of the reaction?
concentration/time or mass/time (e.g - mM/min)
What is k?
The rate constant which represents how fast a reaction is going
A net decrease in ∆G is exothermic, what does this reaction mean?
It is spontaneous
Which bond is broken in ATP?
Beta and gamma (-32kJ/mol)
What is meant by half-life?
The amount of time for half the initial reactant to decrease by half
What is the transition state theory?
Molecules in a chemical reaction need to overcome an energy barrier, known as the activation energy, to be converted from reactants to products. The transition involves passing through a high-energy state known as the transition state.
What is the rate enhancement equation?
kEcat / kuncat
(Ecat = enzyme catalysed reaction)
(uncat= uncatalysed reaction)
What is the relation / proportionality to k and ∆G?
Inversely proportional. If the activation energy decreases, the rate constant increases.
This relationship has a log effect, what does this mean?
A small decrease in the activation energy will lead to a large increase in the rate constant
The ∆G between the reactants and products is unchanged during the use of a catalyst. Enzymes stabilise the transition state which reduces the activation energy.
What is the equation for ∆G?
∆G = ∆H - T∆S
(H = enthalpy = bond making/breaking)
(S = entropy = disorder/order)
(T = temperature)
Changing ∆H, how is general acid-base catalysis carried out?
Acid = transfers H+ proton to the developing -ve charge to stabilise it
Base = accepts H+ proton from the devloping +ve charge to stabilise it
Why is this done?
To prevent the devlopment of ‘naked’ charges
How is electrocatalysis carried out by enzymes to stabilise charge?
The enzyme can have charged sidechains or metal cofactors which stabilise charge
How does chymotrypsin act in electrostatic catalysis?
Its peptide backbone stabilises -ve charge on tetrahedral oxyanion
What about metal ions - Zn2+?
Zn2+ acts as a metal cofactor in carbonic anyhydrase which stabilises the negative charge from oxygen
How can enzymes change the ∆S?
By bringing the substrates into a closer proximity and correct orientation
This changes the reaction from a bimolecular to a unimolecular reaction
What is covalent catalysis?
Where the enzyme contains a reactive group that becomes temporarily covalently attached to part of the substrate (e.g - chymotrypsin)
What is competitive inhibition and when can the enzyme still. function efficiently?
When an inhibitor binds to the active site of the enzyme. If the substrate concentration is high enough, the enzyme can still function as the substrate can outcompete the inhibitor.
What happens to the Vmax during competitive inhibition?
It stays the same because the inhibitor does not directly affect the catalytic activity
What happens to the Km during competitive inhibition?
It is increased. A high Km means a lower affinity for binding between the substrate and active site.
What is Vmax and Km?
Vmax (maximum reaction rate) represents the maximum rate at which an enzyme can catalyze a reaction when it is saturated with substrate. Km is a measure of the affinity between the enzyme and the substrate. It represents the substrate concentration at which the reaction rate is half of the maximum reaction rate (Vmax/2).
What is non-competitive inhibition?
The inhibitor binds to a site elsewhere to the active site, causing the enzyme to have a conformational change and reduce its catalytic activity
What happens to the Vmax and Km during non-competitive inhibition?
Vmax is reduced because the catalytic activity is reduced. Km is unchanged because the affinity of the enzyme is unaffected.
What is Kcat?
The turnover number
What does the turnover number represent?
The turnover number is the number of substrate molecules converted to product per enzyme molecule per unit time. It is not a direct count of the number of molecules but rather a rate constant.
E.g - Let’s say an enzyme has a kcat value of 100 s^-1. This means that, on average, each enzyme molecule can convert 100 substrate molecules into product per second when it is fully saturated with substrate.
What is the equation for Kcat?
Kcat = Vmax / [E]
What is the specificity constant?
The specificity constant, kcat/Km, provides a measure of the catalytic efficiency of an enzyme for a specific substrate. A higher specificity constant indicates a more efficient enzyme-substrate interaction and a faster rate of conversion of substrate to product. It is often used to compare and evaluate the efficiency of different enzymes or different enzyme-substrate pairs.
