Enzymes Flashcards
What is the transition state of a reaction?
High energy intermediate that lies between S and P
What is the activation energy of a reaction?
Minimum energy S must have to allow reaction
How can you increase the rate of a reaction?
Increase the number of molecule with activation energy
Increase chance of molecular collisions
E.g. Temperature, concentration and enzymes
What is an enzyme?
Biological catalyst that increases the rate of a reaction by lowering the activation energy
Facilitates formation of the transition state
What are some important features of enzymes?
Highly specific Unchanged after the reaction Do not affect the reaction equillibrium Increase rate of reaction Proteins May require associated cofactors
Why are we interested in enzymes?
Inheritable genetic disorders
Overactive enzymes can cause disease
Measurement of enzyme activity for diagnosis
Inhibition of enzymes by drugs
What is the active site?
The place where substrates bind and where the chemical reaction occurs
Formed from amino acids at different parts of the primary sequence
Clefts or crevices
Have a complementary shale to substrate- lock and key
The active site forms a complementary shape after binding- induced fit
Bound by weak bonds
How do enzymes work?
Substrate binds with enzyme active site to form enzyme substrate complex
Enzyme changes shape of substrate - ES transition
Product forms
What happens if you increase the amount of substrate in a reaction?
Amount of product will increase until maximal amount of enzyme substrate complexes form
What causes enzymes to denatures?
Temperature and pH
What is the Michaelis-Menten model for enzyme catalysis?
A specific complex between the enzyme and the substrate is a necessary intermediate in catalysis
Not all enzymes obey this model
What is vmax?
The maximal rate when all enzymes active sites are saturated with substrate
What is km?
Substrate concentration that gives half maximal velocity
What does a low km mean?
High affinity for substrate
What does a high km mean?
Low affinity for substrate
What is vmax measured in?
It is a rate so 1 unit is the amount of unit that converts 1 micromol of product per minute under standard conditions
What is a lineweaver-Burke plot?
Allows for easy estimation of km and vmax
What is an enzyme inhibitor?
Molecules that slow down or prevent enzyme reactions
What is an irreversible enzyme inhibitor?
Binds very tightly
Generally convalent bond
E.g. Nerve gas
What is a reversible enzyme inhibitor?
Not covalent so can dissociate freely e.g. Competitive- binds at active site
Non-competitive- binds at allosteric site
What do competitive inhibitors affect?
Km
What do non-competitive inhibitors affect?
Vmax
What happens when you add more substrate when competitive inhibitor is present?
Will overcome effect of inhibitor so no effect on v max
But as competes for active site km increases
Why does the non- competitive inhibitor lower vmax?
Decreased the turnover number of the enzyme
