Term
| First and Second Law of Thermodynamics |
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Definition
1st: Energy is conserved; cannot be created or destroyed
2nd: Entropy (S) tends to increase |
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Term
Define the change in free energy (delta G) and delta G for a reaction.
dG=0 is...
dG<0 is...
dG>0 is... |
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Definition
-Amount of free energy consumed or liberated during a chemical reaction
dG=0 is...Equilibrium
dG<0 is...Spontaneous (Exergonic)
dG>0 is...Energy needed (Endergonic) |
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Term
| Equation relating dG (and dG0') to [products] and [reactants] |
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Definition
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Term
How do enzymes acts as catalysts?
How do they affect Gibbs free energy of activation? |
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Definition
-Do not change eq of chemical rxn, but stabilize transition state
-Lower activation energy |
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Term
| Induced Fit vs Lock-and-Key |
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Definition
Induced Fit: substrate binds to the enzyme's activation site in which it mostly fits, enzyme then changes shape to better fit the substrate
Lock and Key: substrate binds to a specific enzyme at the activation site in which it fits perfectly
In reality, both of these occur |
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Term
| 4 properties of enzyme catalysts |
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Definition
1. Specificity
2. Stabilize transition state, do not change thermodynamics
3. Do not change [S] and [P] at Keq, but decrease amount of time required to reach eq
4. Bring substrates together at optimal orientation in the active site |
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Term
| Draw the Michaelis-Mentin kinetics profile of an enzyme |
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Definition
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Term
Define and give units for:
Vmax
Km
Kcat
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Definition
Vmax (μmol product/min/mg enzyme) is velocity of reaction when all enzyme active sites are filled
Km (mM or μM) is [S] at (1/2)Vmax and measures affinity for substrate (High Km=Weak Binding, Low Km=Strong Binding)
Kcat (s-1) is turnover rate
Kcat/Km (s-1M-1) measures catalytic efficiency |
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Term
| Why are enzymes with very high Kcat/Km ratios efficient catalysts? |
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Definition
· A high Kcat indicates a high number of enzymatic reactions catalyzed per second.
A low Km indicates strong binding between substrates and enzymes
High divided by low gives very high ratio indicating that a large number of reactions can be catalyzed at maximum efficiency |
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Term
| Explain the kinetics of Zero, First, an Second order reactions |
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Definition
Zero: independent of [S]
First: 1 substrate, rxn rate dependent on [S] and decreases over time as less substrate is available (half life)
Second: 2 substrates, rxn rate dependent on both [S]s |
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Term
| Reversible vs Irreversible Inhibition |
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Definition
Reversible: non-covalent bond b/w inhibitor and enzyme; can be removed and enzyme reused
Irreversible: covalent bond between inhibitor and enzyme; permanently inhibits enzyme
(Ex: Penicillin, Sarin) |
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Term
Reversible Inhibition: Competitive
What is it? Effect on Km and Vmax?
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Definition
Inhibitor structurally resembles substrate and binds to active site
Increase Km
No change Vmax |
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Term
Reversible Inhibition: Noncompetitive
What is it? Effect on Km and Vmax? |
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Definition
Inhibitor binds to allosteric site, affecting shape of active site so substrate doesn't quite fit
No change Km
Decrease Vmax |
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Term
| Why is phosphorylation by kinases linked to the energy status of the cell? |
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Definition
-Kinases phosphorylate Serine, Threonine, or Tyrosine (have OH groups)
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Term
Catalytic Triad
What is it? What's the mechanism? What does it do?
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Definition
-Refers to three amino acid residues functioning together at active site of certain hydrolase and transferase enzymes
-Generates nucleophilic residue for covalent catalysis by creating charge-relay network to polarize and activiate the nucleophile, which attacks the substrate, forming a covalent intermediate which is then hydrolyzed to regenerate the free enzyme.
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