EXAM 3 (2) Flashcards
A given enzyme has a range of specificity for its substrate that is…
Very narrow
T/F. Enzymes bind to their substrates at a region on the substrate called an active site.
False
Enzyme cofactors are _______ bound to the proteins?
Non-covalently
Enzyme prosthetic groups are _________ bound to the enzyme
Covalently
Binding of an enzyme to its substrate ________ its activation energy.
Lowers
T/F. Transition state analogs are structurally stable molecules with a very short half life.
False
The enzyme mechanism that yields only about 100 fold increase in reaction rate enhancement
Acid-base Catalysis
T/F. The pre-steady state is a period where ES build up equals the ES breakdown.
False
Kcat is an abbreviation for
Catalytic Rate
Combined constant rate
Km
T/F. When Vmax equals 2V, Km equals substrate concentration.
True
T/F. Up to a point, Vo increases the substrate concentration is increased.
True
Double reciprocal plot such as Lineweaver-Burk Plot are used in enzyme kinetics analysis to get a more accurate
Vmax
When an inhibitor of an enzyme binds on to ES complex, the inhibition is
Uncompetitive
_______________ is the alternative name given to the mechanism based inactivator.
Suicide Inhibitor
Two major types of Regulatory Enzymes
Covalent Modification or Allosteric Enzyme
The only known example of a nonprotein biological catalyst
rRNA
When every enzyme molecule in a reaction mixture is bound to a substrate, the enzyme is said to be __________.
Saturated
Method said to determine properties of enzymes of very hydrophobic substrates, such as lipids
Surface Dilution Kinetics
The period of time an enzyme catalyzed reaction and concentration of the enzyme substrate compile remains stable is called
The Steady-State
Michaelis and Menten assumed for a period of time the enzyme catalyzed reaction formation rate of the enzyme substrate complex is essentially equal to the breakdown of the enzyme substrate complex. This is known as
The Steady-State Assumption
Add phosphate
Kinases
Remove phosphate
Phosphatases
List the 6 classes of Enzymes in order with their EC number.
EC.1.X.X.X… OTHLIL
What does EC stand for?
Enzyme Commission
Specificity constant =
Kcat/Km = m^-1s^-1
Mole
Unit that describes the number of particles;
One gram molecular weight of a complex; A mole contains 6.02 X 10^23 atoms of any element
Molarity
Unit of concentration of mol/L
Active Site
Where the substrate binds to the enzyme; inhibitors may also bind here; site of catalysis
Transition State
Arrangement of unstable, highly energyed atoms in which bonds are being broken and formed
Acid-Base Catalysis
When a proton is transferred during the transition state; Glue, His, Tys, Cys R-groups can act as either an acid, protinated, or base, unprotinated
Allosteric Regulation
Reversible noncovalent binding of modulator molecule the occurs NOT at active site
Covalent Modification
Reversible, covalent addition of group to enzyme; Modification occurs to specific amino acid
Inhibitor molecule resembles substrate molecule and competes for binding at active site
Competitive Inhibition
Same Vmax
High I = low Vmax
The effect on Km with no observable effect on Vmax
Diagnostic Competitive Inhibition
Inhibitor binds to a site located away from active site
Noncompetitive Inhibition
Same Km
Inhibitor will bind only to ES complex
Uncompetitive Inhibitor
Become reactive after binding to active site and instead of being converted to normal products it is converted to a highly reactive product that binds irreversibly to enzyme
Suicide Inhibitors
Reaction product of one enzyme becomes the S of the next enzyme and so on
Regulatory Enzymes
One enzyme sets the rate of the overall sequence because it catalyzes the slowest ______ ________ step
Rate Limiting
This is the regulatory enzyme aka rate limiting enzyme
Each metabolic pathway is ______ _________ to meet changes in cellular demand
Constantly Adjusted
Reversible, noncovalent binding of modulator molecule to change conformation
Allosteric Enzyme
Many times the allosteric enzyme is inhibited by the ________ _______. Regulation of this type is ______________.
End Product
Feedback Inhibition
Reversible, covalent addition of a group to enzyme and modification occurs to specific amino acids
Covalent Modification
Vmax
Max Velocity
Km
Michaelis-Menten Constant
Combine Rate Constant
Kcat
Turnover number
Catalytic Rate
Product Formation Rate
Specificity Constant
kcat/Km = m^-1s^-1
Catalytic Rate
kcat
Modulate Enzyme activity
Effectors (Activators or Inhibitors)
__________ depends on how efficiently reactants can reach a transition state.
Rate of Reaction
Stable structures that resemble transition state structures
Transition State Analogs (inactivates enzymes)
Reaction rate between two molecules is enhanced when enzyme removes them from dilute solution and holds them in close proximity to each other in the active site
Facilitation of Proximity
Mechanism that raises the effective concentration of reactants
Facilitation of Proximity
A means to artificially raise reactant concentration so the reaction is faster
Facilitation of Proximity
Amino acid in active site with nucleophilic R-groups attack electrophilic parts of the substrate forming covalent bonds between E and S
Covalent Catalyst
Usually happens with transferases
Covalent Catalyst
Transfer of a proton in the transition state
Acid-Base Catalysis
Rate enhancement is only about 100
Acid-Base Catalysis
Groups that can act as acid or base in Acid-Base Catalysis
Glu, His, Tyr, Cys
This mechanism is dependent on pKa of the R-groups that are in the active site and on pH optimum of the enzyme
Acid-Base Catalysis
Strain is induced in the bond system of the reactants and the release of the strain as the transition state converts to products provides the rate enhancement when the substrate is removed and converts into product
Molecular Distortion/Strain
When enzyme binds to active site, strain is placed on reactant
Molecular Distortion/Strain
Molecular Distortion/Strain
When enzyme binds to active site, strain is placed on reactant and substrate is highly energized. Enzyme lets go and that releases the energy in the transition state to push the substrate into product
Typically employed in assaying lipid-dependent enzyme activity
Mixed Micelle System
Mixed micelle system is composed of
Nonionic detergent Triton X-100 and lipid
Alternative enzyme kinetics for hydrophobic enzymes and substrates
Surface Dilution Kinetics
3-D bulk interactions
Clumps of insoluble material
Interactions between enzyme and substrate where substrate is not associated with micelle
2-D Surface Interactions
Occur on the membrane
Lineweaver Burk Plot
Double Reciprocal Plot
x-int = 1/-Km (same units as substrate)
y-int = 1/Vmax (same units as Velocity)
Eadie-Hofstee Plot
y-int = Vmax/Km x-int = Vmax
Competitive Inhibition Graph
Same Vmax
Slope = Km/Vmax
Noncompetitive Inhibition Graph
Same Km
x-int = 1/-km
Uncompetitive Inhibition Graph
3 Parallel Lines
S and I (not S1 and S2 like Ping Pong)
Ternary Complex Formation
Random Binding = Doesn’t matter
Ordered Binding = Conformation of Enzyme is altered with substrate which allows S2 to bind
Ping Pont
Three parallel lines S1 and S2
Enzyme catalyzes before substrate comes in
Enzyme can only bind to S2 in modified form
A direct measure of reaction efficiency
kcat/Km
Substrate Specificity
kcat/Km
High if Enzyme and substrate like to bind
Per-steady state
ES builds up
Steady state
ES remains constant
