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
Describe the 2 models of enzyme specificity. Which one accurate?
- Lock and key (inaccurate)
- Substrate (reactant) binds to the enzyme perfectly - Induced fit
- 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 3 critical aspects of enzymes?
- Usually bind to substrates with high affinity and specificity
- Active sites (binding pockets) in the enzyme bind to the substrate and promote catalytic reactions - Substrate binding to the active site induces changes in the enzyme
- Enzyme activity is highly regulated in cells
What are the 4 modes of enzyme regulation?
- Bioavailability
- Catalytic efficiency (Activity enzymes regulate covalent modification)
- Covalent modification
- Allosteric regulation (similar to hemoglobin)
How are enzymes chemical catalysts?
- Alter the reaction rate without changing theratio of substrates and products at equilibrium
- Lower the activation energy
- They do NOT change the overall ΔG of the reaction
What is a cofactor?
A small inorganic molecule that aids in the catalytic reaction mechanism within the enzyme active site
What is the function of a cofactor?
Provide additional chemical groups when amino acid functional group are insufficient
What is a coenzyme?
An organic enzyme cofactor
What is NAD+/NADH?
A required component in many redox reactions involving dehydrogenase enzymes
What is a prosthetic group?
A coenzyme that is permanently associated with an enzyme
How does pH/temperature affect enzymes?
Certain enzymes work best at certain pH/temperature –> if you decrease/increase pH/temperature, enzyme activity will decrease
What are the 3 major ways that enzymes increase the rate of a reaction inside cells?
- Stabilize the transition state
- Provide an alternative path for product formation
- Orient the substrates appropriately for the reaction to occur
What is lipoamide? What is its role in catalysis?
- Temporary carrier of acetyl group in reaction catalyzed by pyruvate dehydrogenase
- 2 carbon transfer
How do enzymes catalyze reactions?
- Enzymes bring substrates together
- Geometric and chemical complementarity
- High local concentration
- Optimal orientation
- Bind via non-covalent interactions
What features of the enzyme active site contribute to catalyzing a reaction?
- Provide an optimal orientation of the substrate relative to reactive chemical groups
- Excludes excess solvents
- Binding interactions between substrate and enzyme create a transition state
- Presence of catalytic functional groups
- Sequestered microenvironment of the active site
What facilitates the formation of the transition state?
Bonding interactions of the substrate in the enzyme active site
What inhibits enzymes?
Transition state analogs (stable molecules that mimic the transition state at the active site)l
What are the 3 types of catalysis?
- Acid-base catalysis
- Covalent catalysis
- Metal ion catalysis
What are the 2 types of acid-base catalysis?
- Specific (involves water)
- General (proton transfer involves functional group)
What are the 3 general categories of enzyme-mediated reactions in cells?
- Coenzyme-dependent redox reactions (in lots of metabolic pathways!)
- Metabolite transformation reactions (in anabolic and catabolic reactions)
- Reversible covalent modification reactions (attach/remove molecular tags; recognition)
What are serine proteases?
Enzyme that cleaves the peptide backbone of proteins
What types of catalysis does chymotrypsin use?
- Acid-base catalysis
- Covalent catalysis
What does chymotrypsin do?
Cleaves (hydrolyzes) peptide bonds
