Enzymes & Enzyme Kinetics Flashcards
What are enzymes ?
They are biological catalysts, which are not chemically altered in a reaction.
What is the function of enzymes ?
They increase the rate of a reaction by providing a pathway of lower activation energy, to get reactants to products.
Physiological conditions
Moderate temperature
Neutral pH
Low concentrations of substrate
Aqueous environment
What are some features of enzymes ?
Active site
They have a very high specificity
What is meant by rate enhancement ?
The factor by which a catalyst increases the rate of a reaction.
Rate enhancement equation
Catalysed rate / Un-catalysed rate
Disease
Enzyme deficiencies can cause disease.
e.g. PKU
How are enzymes involved in diagnosis ?
The concentration/ activity of enzymes allows you to make a diagnosis.
How are enzymes involved in drug therapy ?
Many drugs are enzyme inhibitors. The specific dosage is related to the inhibition mechanism.
Function of lysozyme
Catalyses the cutting of polysaccharide chains
Lysozyme action
Lysozyme binds to the polysaccharide chain, catalyses the cleavage of a specific covalent bond and releases the cleaved products.
Vo
Initial reaction velocity
The speed at which the reaction proceeds before other factors come into play.
What happens to the reaction velocity when substrate concentration increases ?
Vo increases
How is Vo measured ?
By increasing the substrate conc. and measuring the accumulation go products over time.
What does the enzyme activity depend on ?
How rapidly the enzyme can process the substrate
What is Km ?
Michaelis-Menten constant
The substrate concentration required for half the maximum velocity.
What are enzyme inhibitors ?
Chemicals that interfere with enzyme reactions.
What are the 2 types of enzymes inhibitors ?
Irreversible
Reversible
Irreversible inhibitors
Inactivators
Reversible inhibitors
Competitive
Allosteric (Non-Competitive)
What do irreversible inhibitors do ?
They react with the enzyme and form a covalent adduct with the protein.
Competitive inhibition action
A competitive inhibitor can compete with the substrate for the active site of an enzyme.
What is an analogy to describe competitive inhibitors ?
A key that gets through the keyhole but can’t unlock the door.
With competitive inhibition on a Lineweaver Burke plot what is the effect of adding more competitive inhibitor.
X-intercept shifts closer to 0
Y-intercept stays the same
Allosteric meaning
Allosteric inhibitors bind to the enzyme at the same time as the substrate but at a different site, called the allosteric site.
Results of allosteric inhibition
Vmax decreases
Km often (but not always) increases
With non-competitive inhibition on a Lineweaver Burke plot what is the effect of adding more non-competitive inhibitor.
X and Y intercept shift away from origin
For competitive inhibition what happens to Vmax and Km
Vmax - unchanged
Km - increases
For non-competitive inhibition what happens to Vmax and Km
Vmax - decreases due to reduced efficiency of reaction
Km - unchanged
For mixed inhibition what happens to Vmax and Km
Vmax - decreases due to inhibition
Km - increases as substrate affinity in reduced
