Enzymes Flashcards
What are cofactors
Additional components to aid catalytic activity
What are the three types of Co-factors
Metals, Prosthetic groups and co-enzymes
Which type of reaction is catalysed by Oxidoreductases
Redox Reactions
Which type of reaction is catalysed by Transferases
Group Transfer Reactions
Which type of reaction is catalysed by Hydrolases
Hydrolysis reactions
Which type of reaction is catalysed by Lyases
Addition/removal of groups to form double bonds
Which type of reaction is catalysed by Isomerases
Isomerisation Reactions
Which type of reaction is catalysed by Ligases
Ligation reactions of two substrates at the expense of ATP hydrolysis
Can Enzymes effect equilibrium
No, they help to reach equilibrium faster
What 4 parameters affect enzyme activity
pH
Temperature
Enzyme concentration
substrate concentration
How does pH affect enzyme activity
Affects in particular ionisable amino acids
Alters the structure of the active site
Affects catalytic ability or substrate binding ability
How does Temperature effect enzyme activity
Increases the rate of enzyme-catalysed reactions
the interactions that determine the 3D shape of the enzyme become disrupted with further increases in temperature
The longer the incubation time, the more noticeable the effects
What can impact Thermolability
Mutations that can disrupt the stability in the expected temperature range (denature faster than expected)
How does enzyme concentration impact enzyme activity
increasing the concentration of the enzyme increases its activity
This is until the substrate becomes limiting
What is the Vmax of an enzyme
The fastest theoretical speed the enzyme can work at
What is the Kcat of an enzyme
How many reactions an enzyme can catalyse per unit time (specific to an enzyme)
What is the formula to calculate Kcat
Kcat = Vmax/[E]
What is the Km of an enzyme
the amount of substrate required to reach 1/2Vmax
What is the Km used for
The substrate concentration that most sensitively affects enzyme activity
What does lipoprotein lipase do
Releases fatty acids from circulating lipoproteins so that the free fatty acids can be taken up by surrounding tissues
Released by both adipose tissue and skeletal muscle
Why does adipose tissues LPL have a high Km
The rate of FA release is dependent on LPL protein levels
After a meal, LPL levels are high
Adipose LPL are highly active, and the free fatty acids released can be stored in the adipose tissue
Why does skeletal muscle LPL have a low Km
The rate of FA releases is dependent on the [LPL] as the enzyme is saturated at low LPL levels
After a meal, activity does not increase any further, as the enzyme is saturated
Between meals, the amount of free fatty acids released from LPL id dependant on how much LPL is secreted by the muscle
What is co-operativity
When the substrate also binds to another active site on the enzyme, affecting activity
What is negative co-operativity
Increased substrate concentration inhibits the activity of the enzyme
What is positive co-operativity
When increased substrate activity increases the activity of the enzyme
What is Irreversible inhibition
Permanently modifies the enzyme, often covalently
Km unaltered
Vmax decreases
What are reversible inhibitors
Inhibitors bind to the enzyme or enzyme complexes via hydrophobic, ionic or van Der Waals intreactions
What are competitive inhibitors
Compete with the substrate for the active site of the enzyme
normally have a similar structure
make it more difficult for the actual substrate to bind to the active site
The activity of the enzyme remains unchanged, so the Vmax does not change
more substrate required to achieve results, so the Km increases
How do you overcome competitive inhibitors
Increase the concentration of substrate
What are statins
used to lower the cholesterol in the blood, in order to prevent CVD
How much do statins decrease plasma [LDL]
30-60%
What are uncompetitive inhibitors
the binding of the substrate results in the a binding of the inhibitor, forming an unproductive ESI complex
This draws the E/ES equilibrium towards ES.
Lower Km
Lower Vmax
What concentration are uncompetitive inhibitors more effective
high substrate concentrations
What are non-competitive inhibitors
Inhibitor can bind to either E or ES doesn't alter binding prevents catalysis Decreases the concentration of functional enzyme Vmax decreases Km unaffected
What are protein kinase inhibitors
Typically ATP competitive inhibitors with low specificity but a high affinity
