Chapter 2 - Part 2 Flashcards
What is k_cat
How fast an enzyme converts substrate into a product.
What is the catalytic efficiency of an enzyme? other name?
The catalytic efficiency (SPECIFICITY CONSTANT) of an enzyme is defined as kcat/Km. Higher means higher affinity for a particular substrate. It makes sense, because this term increases as the equilibrium constant forward increases and the amount of substrate necessary to get to half of the max velocity decreases. An enzyme that makes the reaction even faster with less substrate is definitely more efficient.
What is a Line-Weaver Burke Plot?
A Line-Weaver Burke Plot is a modified Michaelis-Menten equation. It measures 1/v and 1/s instead of v and s. For this reason, Line-Weaver Burke Plots are often called double reciprocal graphs. These plots are used because they represent the equation behind enzyme kinetics in the form of a straight line.
The x-intercept of the Lineweaver Burke Plot gives us the
-1/Km
The y-intercept of the Lineweaver Burke Plot gives us the
1/vmax
What is a cooperative enzyme?
A copperative enzyme is an enzyme with multiple active sites that affect one another. Generally speaking, these active sites are either in the low-affinity tense state (T) or the high affinity relaxed state (R). Binding of substrate to one site increases likelyhood that other sites will bind substrate (they transition to R). When substrate leaves, other sites transition back to T and make other substrates leave. Example: Hemoglobin binding oxygen
What is the Hill’s coefficient?
The Hill’s coefficient is a mathematical representation of the cooperativeness of an enzyme.
If the Hill’s coefficient is greater than 1, then the binding of one ligand increases the affinity of the enzyme for more ligands, and positive cooperative binding is occuring.
If the Hill’s coefficient is less than 1, then the binding of one ligand decreases the affinity of the enzyme for more ligands, and negative cooperative binding is occuring.
If the Hill’s coefficient is equal to 1, then the binding of one ligand does not affect the affinity of the enzyme for more ligands, and no cooperation is occuring.
How do enzymes respond to the environment?
Enzymes are very sensitive to their environment! Enzymes are, fundamentally, just big molecules, and so messing with the salinity, temperature, ph, etc. of the environment can affect the way they operate.
How do increases in temperature affect enzyme kinetics?
Generally speaking, the velocity of an enzyme catalyzed reaction will double for every 10C° increase in temperature (more energy to react!) until the optimum temperature for the enzyme is reached (body temperature for most enzymes in the body). After this temperature, there is so much energy that the bonds holding the enzymes together break, which causes a sharp decrease in the velocity of the reaction.
How do changes in pH affect enzyme kinetics?
Enzymes have a specific pH at which they function most effectively. Any deviations from this pH will cause the enzyme to lose functionality. For most enzymes in the human body, this is equal to the blood’s pH of 7.4, but there are notable exceptions such as digestive enzymes. Pepsin in stomach works at pH 2 and pancreatic enzymes in small intestine work at pH 8.5
After an enzyme is denatured due to heat, is it possible to cool it back down and renature it?
Sometimes! It really just depends on the enzyme. Some can regain their original function. Others, once denatured, are permanently non-functional.
What is feedforward regulation?
Feedforward regulation is a relatively rare phenomenon in which enzymes further down in a chain of reactions are regulated by products produced earlier in the pathway.
What are the 4 types of reversible inhibition?
- Competitive Inhibition
- Noncompetitive Inhibition
- Uncompetitive Inhibition
- Mixed Inhibition
What is reversible inhibition?
Reversible inhibition means that the inhibition of the enzyme is accomplished through weak interactions that can be relatively easily displaced, and therefore the inhibition of the enzyme can be reversed.
What is irreversible inhibition?
Irreversible inhibition means that the inhibition of the enzyme is accomplished through covalent bonds that permanently inhibit the activity of the enzyme.
How does a competitive inhibitor affect Vmax, Km, and the lineweaver burke plot?
Competitive inhibitors compete with the substrate, which increases the amount of substrate you need to get equal catalysis, which increases Km.
Competitive inhibitors are out-competed so hard at high substrate concentrations, that they do not affect the enzyme, which means that competitive inhibitors do not change v max.
The lineweaver Burke Plot for a competitive inhibitor will have a right shifted x-intercept with no change in the y-intercept.
How does a non-competitive inhibitor affect Vmax, Km, and the lineweaver burke plot?
Copies of the enzyme that remain active still have same affinity for substrate, so Km is unchanged.
At high concentrations of substrate, the non-competitive inhibitor will still occupy its allosteric site and inhibit the enzyme, which means vmax is lowered.
The lineweaver Burke Plot for a non-competitive inhibitor will have a higher y-intercept with no change in the x-intercept.
What is noncompetitive inhibition?
Noncompetitive inhibition is when an inhibitor binds to an allosteric site somewhere on the enzyme that causes it to change its shape and reduce its function. Bind Equally well to enzyme and ES complex. Because the noncompetitive inhibitor is not competing with the substrate, increasing the concentration of substrate will not reverse the inhibition.
What is uncompetitive inhibition?
Uncompetitive inhibition is when the inhibitor only binds allosterically to the enzyme-substrate complex and locks it up, preventing the release of products.
How does an uncompetitive inhibitor affect Vmax, Km, and the lineweaver burke plot?
Uncompetitive inhibitors make the enzyme substrate complex so stable that it won’t release the substrate. This means you need less substrate to reach half of vmax, which means Km is lowered.
Uncompetitive Inhibitors cannot be outcompeted at high concentrations of substrate, which means that the vmax of the enzyme is lowered.
The lineweaver Burke Plot for an uncompetitive inhibitor will have a higher y-intercept with a left shift of the x-intercept. The decrease in km and vmax is proportional, so the new inhibition line will have the same slope as the uninhibited one.
What is mixed inhibition?
Mixed inhibition is when an inhibitor can bind to the enzyme or the enzyme substrate complex, but with different affinity. If inhibitor preferentially binds to enzyme it increases Km, if it preferentially binds to ES complex it lowers Km. The Vmax is always lowered in mixed inhibition.
What is an allosteric site?
An allosteric site is a portion of the enzyme that can be bound by allosteric molecules to inhibit or activate the enzyme.
What are two common covalent modifications made to enzymes for regulatory or functional purposes?
- Phosphorylation and dephosphorylation
- Glycosylation (covalent attachement of sugars)
What is a zymogen?
A zymogen is an inactive form of an enzyme that must be modified to activate it. The creations of zymogens is a way to further regulate and control the activity of dangerous enzymes in the body (digestive enzymes). Most zymogens have the suffix -ogen.
