Lecture 4: Enzymes Flashcards
What are a few reasons to use proteins as catalysts?
Milder Conditions
Higher reaction rates
Greater reaction specificity
Capacity for regulation
Are enzymes globular proteins?
Yes;
What are ribozymes
Enzymes that catalyze RNA reactions
What is the name of the molecule that is catalyzed?
Substrate
True or False; Active site residues also contribute to substrate specificity
True
What does ES stand for?
Enzyme- Substrate (Complex)
What is the top of the energy hill?
Transition State
True or False; Increase in AE (Activation Energy) decreases rate of reaction
True AE/ROR are opposite
True or False; enzyme lowers Delta G and decreases reaction rate
False; lower delta G= increase in reaction rate
Does the enzyme lower the AE?
Yes;
Does the enzyme change the reaction eq.?
No; it does not have effect on the equilibria
What is the major difference between the S & P transition state?
Activation Energy
What are (3) ways enzymes lower AE?
(1) Rearrange covalent bonds
(2) Bring reactive groups closer
(3) Stabilize transition state
What is the rate limiting step?
Step with the highest activation energy
What is the formation and decay of transient chemical species?
Reaction Intermediates
How do you stabilize the transition state?
Form weak covalent bonds bt. enzyme and substrate to lower activation energy?
True or false; Different energies are used to for catalysis and enzyme specificity
False; same energy is used in both.
The E-site is used to form a variety of ______ interactions.
Weak interactions
What is kinetics?
Study of the rate at which compounds react
Are irreversible inhibitors promiscuous?
Yes; they are toxic and bind to anything (sleep with everyone)
How are reversible inhibitors used as drugs?
slow down a specific enzyme
What are (2) ways in which reversible inhibitors bind?
(1) free enzyme and prevent the binding of the substrate
(2) enzyme-substrate complex and prevent the reaction
What are (3) types of inhibition?
(1) Competitive
(2) Uncompetitive
(3) Noncompetitive (mixed)
True or false: Kd=Km
True
What is 1/Ka?
Kd (disassociation constant)
What does Competitive Inhibition bind to?
Active Site of Free Enzyme
What is Competitive Inhibition Km & Affinity?
Km increases
Affinity decreases
What is Competitive Inhibition y-max & Vmax?
stays the same
What does Non-Competitive Inhibition bind to?
Active site of the free enzyme
ES complex and varying affinity
What does Un-Competitive Inhibition bind to?
Allosteric Site of ES Complex
What happens to the Km and Affinity of Un-Competitive?
Km- decreases
Affinity- Increases
What happens to the y-max and v=man of Un-Competitive?
They both decrease
What is another name for irreversible inhibitors
Suicide substrate
Describe Competitive Inhibition Graph
Lines intersect at y-axis
Describe Uncompetitive Inhibition Graph
Lines are parallel
What is another name for mixed inhibition
Non-competitive
Where does covalent modification occur?
Irreversible Inhibtion
Describe Mixed Inhibition Graph
Lines intersect at y-axis
What is a protease?
Enzyme that cleaves peptides on the C-terminal side of Aromatic AA’s.
True or False; Proteases hydrolyze the peptide bond
True
What are the three AA that make up the Catalytic Triad
Ser195
His57
ASP102
In general base catalysis, what extracts the proton?
Amino Acid extracts the proton
In general base catalysis, AA acts as a _____ removing___ from H2).
Base; Proton
What is removed from H2O in AA catalysis?
-OH
What (2) items must we remember about General-Base Catalysis?
(1) Protein Extraction by a weak base
(2) Typically via groups other than -OH from water
What is General Acid Catalysis
AA donates a proton
Where is peptidoglycan found?
Cell Walls
What type of enzyme is lysozyme?
antibacterial enzyme
Dehydration of Lys345 forms what?
What enzyme does that
Double Bond; Enolase
Use of which inhibitors make the max seem lower when inhibitor is not present
Non-competitive/mixed
Use of which inhibitor make the max seem lower when inhibitor is present?
None; max is never high
Use of which Inhibitor-affinity of enzyme for substrate increases
Un-Competitive
