Enzyme Kinetics 1 Flashcards
Define “enzyme (E)”
protein catalyst
Define “catalyst”
speed up reactions without being changed by the reaction
Define “substrate”
reactant(s) in the enzyme catalysed reaction
Define “active site”
area of where the substrate(s) bind(s)
What are enzymes involved in?
all biological processes
What does catalysis offer?
CONTROL
What is “catalysis”?
a process about energy and entropy
What are the conditions of an energetically favourable reaction? (3 conditions)
- delta G is negative (<0)
- spontaneous reaction
- forward reaction occurs
What are the conditions of an energetically UNfavourable reaction? (4 conditions)
- delta G is positive (>0)
- non- spontaneous reaction
- no forward reaction (unless coupled to second energetically favourable reaction)
- reverse may occur
What is “entropy”
a measure of molecular disorder, or randomness, of a system
What is the formula for “dissociation rate”?
dissociation rate constant (k{off}) times by concentration of AB ([AB])
What is the formula for “association rate”?
association rate constant (k{on}) times by concentration of A ([A]) times concentration of B ([B])
Binding of an enzyme to a substrate provides what?
a TRANSITION state
What does the transition state consist of?
enzyme-substrate complex (ES) and enzyme-product complex (EP)
What are the two models for enzyme-substrate binding?
- lock and key
- induced fit
Describe the “lock and key” model
the substrate binds to the active site of the enzyme due to their complementary shapes
Describe the “induced fit” model
the substrate binds to the active site of the enzyme as a conformational change in the tertiary structure occurs to allow for this interaction. The enzyme then returns back to its original shape
Describe “specificity”
an enzyme is specific to the substrate due to the active site
What are/do biological catalysts (do)? (4 answers)
- increases the rate of reactions
- reduces the activation energy
- do NOT alter reaction equilibrium
- generally specific for a single reaction
What is the general equation for enzymatic reactions?
E+S reverse ES reverse EP reverse E+P
What is the stage between E+S and ES called?
catalysis
What can be measured during an ES experiment? (5 answers)
- decrease in substrate
- increase in product
- amount of side product
- amount of time enzyme is BOUND to the substrate
- amount of time enzyme is UNBOUND to the substrate
Can substrates and products have colour?
Yes
What is used to measure very fast reactions?
stopped flow
Can enzymes alter the size of substrates?
Yes
Give an example of an enzyme that alters the size of substrates?
DNA restriction endonucleases
During an enzyme reaction, what changes concentration?
- substrate(s)
- product(s)
The differing physical characteristics of products and substrate can be used to measure what?
Rate of reaction
It is important to understand how fast it goes under what conditions?
different concentrations of substrate available
When characterising an enzyme what do we need to know?
- the maximum rate of an enzyme catalysed reaction
- the affinity of an enzyme
What is the method when changing the concentration of the substrate and enzyme? (4 answers)
1) high concentration (excess) of the substrate and a much lower concentration of enzyme
2) measure the rate
3) decrease substrate concentration
4) measure again
When calculating the rate, what could you measure?
- decrease in substrate
- increase in product
How do you calculate the amount of product produced?
take the INITIAL gradient of slope
How do you calculate the gradient for the slope?
initial velocity - rate (v)
What is the rate (v) formula?
maximum rate of substrate conc. / constant Km + substrate conc.
What is the constant, “Km”?
enzyme affinity for the substrate
How is Km calculated?
1/2 Vmax (maximum velocity) (on y axis) and finding the x coordinate that corresponds
