How do enzymes affect the chemical equilibrium
Enzymes have no effect as they increase the forward and backward reaction
How is catalytic power expressed
The turnover number or catalytic constant (Kcat)
Define Kcat
The number of molecules of substrate that one enzyme molecule can convert in 1 second
What are co-factors
Small molecules not part of the enzyme but are required for activity. These can be metal ions or other organic molecules
Enzymes classifications
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
What is the active site
Part of the enzyme in contact with the substrate. Many weak non-covalent interactions form between the substrate and active site.
How is the active site formed
It is a 3-dimensional structure formed from the folding of the polypeptide chain.
What is the lock and key model
Active sites were initially pictured as a fixed set of chemical groups exactly fitting the substrate.
What is the induced fit model
Continuous change in the conformation and shape of the enzyme in response to substrate binding. Allows a greater degree of specificity as they also have to interact.
What is a transition state
The highest energy state interval along the pathway from substrate to product.
What is the activation barrier
The difference in energy between reactants and the transition state.
How do enzymes speed up the rate of the reaction
They lower the activation barrier by providing an alternative pathway which stabilises the transition state.
Another name for enzyme substrate complex
Michaelis complex
What is a catalytic triad
A group of 3 amino acids found on the active site of some proteases involved in catalysis. They form part of the active site.
Conditions needed for steady state kinetics
substrate»_space; enzyme
How to measure the rates of enzyme catalysed reactions
- Measure appearance of product, or disappearance of substrate (keep pH and T constant)
- In a continuous assay
- Work in conditions where substrate»_space; enzyme
What is the michaelis-menten equation
V=Vmax.[s]/Km+[s] ,where Km is a measure of affinity
How to find Km from a velocity substrate graph
substrate at 1/2 Vmax
How to calculate enzyme efficiency
Kcat/Km
What is the lineweaver-burk plot
- Plot 1/v against 1/s
- y intercept = 1/vmax
- x intercept = -1/km
- gradient = Km/Vmax
What is an eadie-hofstee plot
- A plot of V against V/S
- Gradient = -Km
- X intercept = Vmax/Km
- Y intercept = Vmax
What are thermophiles
Enzymes that retain activity at high temperatures
Arrhenius equation
K=Ae^-Ea/RT , where Ea= Enzyme activation energy
What is am Arrhenius plot
- Plot of LnK against 1/T
- Gradient =-Ea/R
- Y intercept =LnA
What tend to be drugs
Enzyme inhibitors
e.g. Penicillin inhibits enzymes which enabe the bacteria to make a stable cross-linked cell wall.
What is irreversible inhibition
- Some inhibitors react covalently with essentil active site groups leading to permanent inactivation
e. g. nerve gas
What is reversible inhibition
- Compounds bind non-covalently to enzymes, obstructing there activity
- Can be removed by dilutions or dialysis
How are Vmax and Km effected by competitive inhibitors
- No affect on Vmax, but increases Km
- When there is a high S, S will displace the inhibitor, therefore E will always be saturated by S
How are Vmax and Km effected by non-competitive inhibition
- Vmax decreases but no affect on Km
- ESI complex is not able to generate product, therefore binding of I lowers catalytic activity
Regulation by metabolites
- End product inhibition
- Regulation by ATP/ADP/AMP concentrations of enzymes, control molecules bind to the regulatory site
Regulation by regulatory proteins
- 1:1 inhibitors
- Interpreting signal, protein binds to a signal activating it, activated proteins bind to enzymes modifying their activities
Regulation by reversible covalent modification
-Regulation by phosphorylation, attachment of phosphate group to OH groups
Regulation by proteolysis
- Some enzymes are made in an inactive form
- Cleavage of specific peptide bonds lead to their activation
How do enzymes enhance specificity
change between alternate conformations
Allosteric regulatiom
- Co-operativity between identical active sites allows switching from inactive to active conformations
- Binding of regulators to secondary sites allow them to affect this switching