Biochem EX1 - Enzymes Flashcards
What is an enzyme?
An enzyme is a protein that catalyzes a specific biochemical reaction.
What does an enzyme affect and not affect (examples Keq, delta G, activation energy, etc.) in a reaction?
An enzyme affects activation energy. It does not effect Keq or ΔG.
Name two models used to describe enzyme specificity and/or catalytic activity.
The 2 models of enzymes are “lock and key” model and “induced fit” model
What is a prosthetic group?
The prosthetic group is non-protein molecules associated with the active sites of the enzymes.
Name the six classes of enzymes.
Oxidoreductase
Transferase
Hydrolase
Lysase
Isomerase
Ligase
What is the Michaelis-Menten equation, and what do the terms mean?
The Michaelis-Menten equation relates velocity of reaction (V) to substrate concentration ([S]). Plotting these values on an x/y graph yields a curve that is normally a rectangular hyperbola.
In a Michaelis-Menten plot, where is Vmax and how do you find Km?
Vmax is dependent on enzyme concentration, but is found at maximum [S], when all enzyme is converted to ES complex. Km can be found at V=1/2 Vmax.
A Lineweaver-Burk plot is also called a _____ ______ plot. What is plotted, and what are the vertical and horizontal intercepts?
A Lineweaver-Burk plot is a double reciprocal plot. It plots 1/[S] vs. 1/[V]. This creates a linear graph where the y-intercept is at 1/Vmax and the x-intercept is at -1/Km.
What are the advantages of the Eadie-Hofstee plot?
The data is more evenly spaced, and no longer clusters high [S] data together.
What characteristics distinguish a competitive inhibitor from other types of inhibitors?
A competitive inhibitor is distingished on an Michaelis-Menken chart by having the same Vmax value as the uninhibited reaction, but a different Km.
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.
What does the inhibitor react with for competitive, non-competitive and uncompetititve inhibition?
Competitive: The active site. Inhibitor resembles the substrate, and binds at the active site to form an EI complex.
Non-competitive: The inhibitor binds at a site other than the active site. EI and EIS complexes form. (the active site’s conformation is changed)
Uncompetitive: Inhibitor binds with the ES complex (either to E or both E and S at the same time) to form ESI. (think of a lock and key model that is forced to stay together)
What does a sigmoid V versus [S] plot as well as a curved Lineweaver Burk plot indicate?
sigmoid V vs. [S] plot indicates an allosteric enzyme reaction.
A curved L-B plot indicates the same.
An allosteric enzyme is one which is affected by an effector binding to the enzyme in a location other than the binding site. This can increase or decrease the enzyme’s affinity for a substrate.
