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What are the advantages to enzymes? (3 things)
They decrease the activation energy, the specificity, and the fidelity (enantiomers) of a reaction, but not the equilibrium.
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Binding of a substrate to an enzyme induces...
a conformation change called the "transition state"
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Chiral specificity is...
the binding of enzymes to specific enantiomeric conformations of chemicals to produce products of one conformation.
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Descirbe the catalytic cycle
- 1. free enzyme with cofactors(coenzymes)
- 2. substrate enters binding site (induced fit)
- 3. additional bonds are formed (transition-state complex)
- 4. products are released and enzyme returns to original conformation
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How do enzymes lower activation energy?
- 1. put reactants in close proximity
- 2. provides reactive functional groups
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what are optimal conditions for biological enzymes?
Body temp (37C) and pH ~7.4
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Define competitive inhibition
inhibitor compete with substrate for binding site.
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Define non-competitive inhibition
inhibitor binds an alternate site on the enzyme
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Define covalent inhibition, give an example.
binds to and permanently deactivates the enzyme (Asprin - Cyclooxygenase)
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What is allosteric inhibition/activation?
inhibitor binds to an allosteric (other) site and induces a change in the catalytic site to either increase or reduce affinity.
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Allosteric activators bind to...
relaxed enzyme state
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Allosteric inhibitors bind to...
The taut enzyme state.
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What is the difference between the taut and relaxed enzymes state?
taut is less active, has lower affinity, while relaxed is the convers.
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What is Km?
[S](mg/L) needed to produce 1/2 of the Vmax OR bind 1/2 the enzyme.
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Describe Km affinity trends...
- As Km ↑ affinity to substrate ↓
- (more substrate is needed to bind enzymes with lower affinity)
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What is Vmax?
Maximal velocity of the rxn. This is when all of the enzyme is bound to substrate.
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Look over pg15 in Enzymes. Its a graph with the different types of inhibitors on it.
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What is a Lineweaver-Burke plot?
A double reciprocal plot used to look at enzyme kinetics.
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Describe the trends for Km and allosteric manipulation of enzymes.
activators ↓ Km (increase affinity), convers for inhibitors.
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What is a K effector and what does it do?
changes the enzymes Km (affinity), but NOT Vmax
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allosteric enzymes are often the _____ _____ step.
rate limiting
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What are 5 ways that conformational changes regulate enzyme activity?
- 1. substrate binding changes (RvsT)
- 2. allosteric binding (act/inhib)
- 3. phosphorylation
- 4. protein-protein interaction
- 5. proteolytic cleavage (zymogens, blood clotting pathway)
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What does a kinase do? What kinds are there?
Phosphorylates amino acids on their OH functional groups, specifically Serine/Thrinonine and Tyrosine. This is allosteric control.
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What does a phosphatase do?
removes phosphates from proteins, altering protein conformation.
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Describe Glycogen Phosphorylase Kinase Regulation
- 1. ↑ Adrenaline, ↑ cAMP
- 2. ↑ cAMP = activated PKA
- 3. Active PKA ↑ phosphorylation of glycogen phosphorylase kinase (GPK) (gets activated)
- 4. activated GPK phosphorylates glygocen phosphorylase (GP)
- 5. Active GP increases glycogen metabolism in muscles
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What is Glyogen Phosphorylase Kinase?
Rate limiting (slow) step glycogen degredation (liberation of glucose)
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What is PKA? How is it regulated?
Protein Kinase A, a Serine/Threonine kinase (attaches Pi) regulated by cAMP
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How can you increase cAMP levels?
adrenaline/epinephrine stimulation
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How does cAMP activate PKA?
It binds the regulatory subunit, which then dissociates from the catalytic site.
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Name three methods of allosteric control for HMG-CoA reductases
- 1. High cholesterol decreases HMG-CoA synthesis
- 2. High cholesrol increases HMG-CoA breakdown
- 3. Low ATP and glucagon increase phosphorylation of HMG-CoA (inactivates)
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What are three methods of enzyme pathway inhibition?
- 1. control rate limiting step
- 2. product inhibited
- 3. feedback inhibition (end-product)
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How do statin drugs work?
inhibition of HMG-CoA to stop liver synthesis of cholesterol
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Define Oxioreductase, give an example
catalyze red-ox rxns using NAD+, NADP+ as electron acceptors. Includes oxidases, oxygenases, reductases, dehydrogenases
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Define transferase, give an example
transfers functional groups, aminotransferase, carboxyltransferase
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Define hydrolase, give an example
cleaves bonds with water, dipeptidase
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Define lyase
breaks bonds w/o water
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Define Ligase and give example
forms bonds, DNA ligase, citrate synthetase
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Define Apoenzyme
enzyme missing cofactors
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Define Holoenzyme
Enzyme with its cofactors
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Define Metalloenzyme
enzyme that requires metal ions as cofactors
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What metal ions are typically used in metalloenzymes?
Iron, copper, zinc, magnesium
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What are some organic cofactors commonly used in biological systems?
NAD+, NADP+, FAD++
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Define ribosyme
RNA that can self splice
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Define Isozyme
Same enzyme from different tissue, have small differences.
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