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
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 inhibits enzymes?
Transition state analogs (stable molecules that mimic the transition state at the active site)l
What are steps 1 and 2 of the chymotripsin mechanism?
- Polypeptide binds to active site
- His57 removes proton form Ser195 allowing nucleophilic attack by Ser O- on carbonyl carbon of the peptide
What is step 3 of the chymotrypsin mechanism?
-
His57 donates a proton to amino group of substrate resulting in peptide bond cleavage
- Carbonyl-terminal fragment released as first product
What is step 4 of the chymotrypsin mechanism?
- H2O (reactive) enters active site and His57 acts as base and deprotonates water; resulting -OH acts as nucleophile and attacks carbonyl carbon of covalent acyl-enzyme intermediate
What are steps 5 and 6 of the chymotrypsin mechanism?
- His57 donates proton to Ser195 causing cleavage of acyl-enzyme resulting in the release of amino-terminal fragment
- Product 2 is released and catalytic triad is regenerated
What are two other enzymes with the same catalytic strategy as chymotrypsin (binding pocket)?
What is reversible covalent modification?
- Act as molecular switches that turn on and off cell signaling and gene expression
- Include kinases and phosphotases
- ATP is commonly used as a phosphoryl group source
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
What is the Lineweaver-Burke equation?
- Used to draw a double reciprocal plot of the enzyme data
- Easier way to determine Vmax and Km
What does Michaelis-Menten graph look like?
What does a Lineweaver-Burke graph look like?
How do you find Vmax and Km on a Michaelis-Menten graph?
How do you find Vmax and Km on a Lineweaver-Burke graph?
