Ch. 7 Flashcards
What are the properties of enzymes?
- Most enzymes are proteins
- Work under mild conditions
- Increase reaction rate
- Greater reaction specificity
- Capacity for regulation
What are the working conditions of enzymes?
- Neutral pH
- Low temperature below 100ºC
- Atmospheric pressure
What is the lock and key model?
Substrate binds to the enzyme perfectly (not accurate)
What is induced fit model?
- Enzyme is flexible to accommodate the ill-fitting substrate
- Permits a much larger number of weaker interactions between the substrate and enzyme
What are the critical aspects of enzyme structure and function?
- Enzymes usually bind to substrates with high affinity and specificity
- Substrate binding to the active site induces changes in the enzyme
- Enzyme activity is highly regulated in cells
What are the modes of enzyme regulation?
- Bioavailability
- Catalytic efficiency
- Covalent modification
- Allosteric regulation (similar to hemoglobin)
What is a substrate?
Substance an enzyme acts upon
What is an active site?
Binding pocket in an enzyme
What is a cofactor?
A small inorganic molecule, often a metal ion, that aids in the catalytic reaction mechanism within the enzyme active site
What is a coenzyme?
An organic enzyme cofactor
What is a prosthetic group?
Coenzyme that is permanently associated with an enzyme
What are co-substrates?
Loosely bound molecules that are transformed to a co-product during the course of an enzymatic reaction
What is the difference between prosthetic groups and co-substrates?
Prosthetic groups are permanently associated while co-substrates are loosely bound
How are enzymes regulated?
- Bioavailability
- Control of catalytic efficiency through protein modification
gene level vs directly
How does pH/temperature affect enzymes?
Certain enzymes work best at certain pH/temperature –> if you decrease/increase pH/temperature, enzyme activity will decrease
How does activation energy and rate of a reaction in the presence or absence of an enzyme affect entropy?
With enzymes
- Increase rate of reaction
- Reduce entropy by orienting the substrates appropriately
Without enzymes
- Slower rate of reaction
- Higher entropy because the substrate is not oriented properly
What are the 6 classes of enzymes?
- Oxidoreductase
- Transferase
- Hydrolase
- Lyase
- Isomerase
- Ligase
What are the functional groups of enzymes?
Catalytic functional groups in the active site mediate three main types of catalytic reaction mechanisms
What are the types of catalysis?
- Acid-base catalysis
- Covalent catalysis
- Metal ion catalysis
How are enzymes modified to change their activity?
Reversible covalent modification
- Phosphorylation and dephosphorylation (kinases and phosphotases)
- Adding fatty acids
What is allosteric regulation?
- First step of a metabolic pathway is often controlled by a regulated enzyme to maximize the efficient use of metabolic intermediates
- Feedback inhibition: the end product of a pathway functions as an inhibitor of the first enzyme in the pathway (ex: ATCase)
In what directions do positive and negative regulators shift the curve?
- Positive regulators shift curve left
- Negative regulators shift curve right
What is the Michaelis-Menten equation?
- small Km –> more [ES] –> more readily binds to substrate at low [substrate] (greater affinity for substrate)
- large Km –> less [E] –> lower affinity for substrate
Michaelis-Menten graph
What is the Lineweaver-Burke equation?
- Used to draw a double reciprocal plot of the enzyme data
- Easier way to determine Vmax and Km
Lineweaver-Burke graph
Explain enzyme kinetics.
- Quantitative study of the rate of chemical reactions performed
- Involves relating reaction rates to free energy and equilibrium
- Reaction rate = velocity (v)
- Substrate concentration = [S]
- k = rate constant of reaction
- v = k[S]
What is Km on a graph?
- Substrate concentration
- Measures how easily the enzyme can be saturated by the substrate
What is Km with respect to enzyme and substrate?
- Amount of substrate it takes for an enzyme to reach Vmax/2
What is competitive inhibition?
- Inhibitor looks like substrate
- Inhibitor binds to active site where substrate binds
- Km of enzyme increases
- Vmax of reaction stays the same
What is noncompetitive inhibition?
- Inhibitor doesn’t look like substrate
- Inhibitor binds to different site other than substrate binding site
- Km stays the same
- Vmax decreaes
How do you determine the type of inhibition using Km and Vmax?
- Compare graphs with and without inhibitors
- Competitive inhibition: Vmax is unchanged, Km increases
- Noncompetitive inhibition: Vmax decreases, Km is unchanged
How do you find Vmax and Km on a Michaelis-Menten graph?
How do you find Vmax and Km on a Lineweaver-Burke graph?
What are the three major ways enzymes increase reaction rate?
- Lower activation energy by stabilizing the transition state
- Provide an alternate path (intermediates) for product formation
- Reduce entropy by orienting the substrates appropriately for the reaction to occur
