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What is an enzyme?
a protein catalyst for specific biochemical reactions
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What does an enzyme affect?
they speed up reactions by lowering the activation energy of a reaction. Gibbs free energy is altered.
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What does an enzyme not affect?
Keq and deltaG are not affected by enzymes
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Name 2 models used to describe enzyme specificty and/or catalytic activity
- The lock and key model
- The induced fit model
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What is a prosthetic group?
- Small non-protein organic molecule that tightly binds to the enzyme's active site.
- When the prosthetic group is attached, an apoenzyme becomes a holoenzyme
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Name the 6 classes of enzymes
- 1. oxidoreductases
- 2. transferases
- 3. hydrolases
- 4. lyases
- 5. isomerases
- 6. ligases
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What is the michaelis menton equation and what do the terms mean?
- V=Vmax[S]/(Km+[S])
- Km = constant value for specific substrate, Michalis constant
- Vmax = maximum velocity of rxn
- [S] = substrate reaction
- V = velocity of reaction
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In an Michaelis-Menten plot, where is Vmax and how do you find Km?
- Vmax is found when [S] is very high. Where all the enzyme is converted to the ES complex.
- Km is determined by finding [S] when V = 1/2 Vmax
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A lineweaver-burk plot is also called a _________ ______ plot.
double-reciprocal plot
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What are the vertical and horizontal intercepts of the lineweaver-burk plot?
- vertical = 1/Vmax
- horizontal = -[1/Km]
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What is plotted in a Michaelis-Menten plot?
[1/V] vs. 1/[S]
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What are the advantages of the Eadie-Hofstee plot?
It will give more evenly spaced data points, not clustered like the LB plot
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What distinguishes a competitor inhibitor from the rest?
- They bind directly to the active site.
- They can be overcome by increasing [S]
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What does the inhibitor bind with for competitive, non competitive, and uncompetitive inhibition?
- competitive = active site
- non competitive = react w/ enzyme to reduce its effectiveness to bind with substrate
- uncompetitive = bind with the ES complex (irreversible) to form the ESI complex
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What does the sigmoid V vs [S] plot as well as a curved lineweaver-burk plot indicate?
- indicates allosteric enzyme reaction
- positive cooperativity of the enzyme
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On the Lineweaver-Burk plots are the vertical and horizontal intercepts the same or different for a.) competitive, b.) non-competitive and c.) uncompetitively inhibited reactions?
- On Linewaver-Burk plots:
- A) Competitive inhibitors show a steeper slope than uninhibited reactions, but have the same 1/Vmax point.
- B) Noncompetitive inhibitors show a steeper slope, but have the same -1/Km point.
- C) Uncompetitive Inhibitors show the same slope, but shifts the curve left, showing a greater -1/Km value.
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