Enzyme Kinetics (Quiz 2) Flashcards
Enzymes ____________ the rate of the reaction
increase
Enzymes ___________ activation energy for a particular molecular reaction
lower
Can enzymes change substrates or products?
no, enzymes only lower activation energy and the energy of the transition state
What are the 2 requirements for endergonic reactions?
1) enzyme present
2) big positive delta G must couple with a bigger negative delta G
What are the 2 different enzyme models called?
1) lock and key model
2) induced fit model
What is the induced fit model?
-enzyme structure is flexible, not rigid
-enzyme and active site adjust shape to bind substrate
-shape changes also improves catalysis during reaction
Can enzymes be reused/recycled?
yes!!!!!!
What is the active site?
section of enzyme where the substrate will bind
What are enzymes?
-catalysts for biological reactions
-enzymes are proteins
-enzymes lower activation energy for a particular molecular reaction
-enzymes increase the rate of reaction
-enzyme activity is lost if denatured
-enzymes may contain cofactors such as metal ions or vitamins
T/F: most enzymes are free to catalyze both forward and reverse directions
true! substrate can change to product or vice versa
Do enzymes change delta G?
no
by reducing activation energy, the enzyme accelerates reactions-> they do NOT influence reaction equilibrium
Delta G and concentrations of the reactant determines what?
the preferred direction (either an endergonic or exergonic reaction)
define rate limiting step
-regulated step
-slowest reaction step
-overall rate of the reaction is limited to this
-usually irreversible
How does temp affect enzyme activity?
-enzyme activity is measured by products in reaction per second
-there is little enzyme activity at low temps
-enzymes are most active at the optimum temp, which is usually 37 degrees C in humans
-enzyme activity is completely lost with denaturation at high temps
How does pH affect enzyme activity?
-enzymes are at their peak/maximum activity at optimum pH
-may lose enzyme activity in low or high pH
-each enzyme has a different pH optimum but its usually neutral at 7
How does substrate concentration affect enzyme activity?
-increased substrate concentration increases the rate of reaction
-maximum activity is reached when all the enzymes combine with substrate
Vmax is determined by ___________ concentration
enzyme
so if enzyme conc. increases then so does Vmax
also note: substrate concentration cannot change Vmax
Pepsin has an optimum temp at 37 degrees C and an optimum pH of 1.5. What happens if you increase the conc. of pepsin?
rate of reaction increases
Pepsin has an optimum temp at 37 degrees C and an optimum pH of 1.5. What happens if you change the pH to 4?
rate of reaction decreases (bc you’re moving away from optimal pH, enzyme become denatured)
Pepsin has an optimum temp at 37 degrees C and an optimum pH of 1.5. What happens if you run the reaction at 60 degrees C?
rate of reaction will decrease
In the induced fit model, the shape of the enzyme ____________________ when the substrate binds
adapts to the shape of the substrate
Vmax is when all enzymes are saturated with ____________
substrates
What is Km?
substrate concentration at 1/2 of Vmax
Km ________ reflects affinity of an enzyme for its substrate
inversely
so if km increases, affinity decreases
if km decreases, affinity increases
When the velocity is constant and equal to Vmax, the rate of the reaction is said to be _______ order with respect to substrate concentration
zero
at this point in MM kinetics, it is said that the reaction is “enzyme dependent”, this is at the end of the curve
When the substrate concentration is much less than Km, the velocity of the reaction is approximately proportional to the substrate concentration. The rate of the reaction is then said to be _______ order with respect to the substrate
first
at this point in MM kinetics, it is said that the reaction is “substrate dependent”, this is at the beginning of the curve
If substrate concentration = Km, then V0 ____ 1/2 Vmax
=
If substrate concentration < Km, then V0 ____ 1/2 Vmax
< (this is 1st order)
If substrate concentration > Km, then V0 ____ 1/2 Vmax
> (this is 0 order)
Km is a characteristic of the _________
enzyme
Km reflects the ______ of the enzyme for that substrate
affinity
T/F: Km does vary with the concentration of the enzyme
FALSE
What shape is the curve on an MM equation graph?
hyperbolic curve
What are the 3 glucose transporters called?
glut 1, glut 2, glut 4
Where is Glut 1 (glucose transporter) found?
RBCs and BBB
Where is Glut 2 (glucose transporter) found?
liver
Where is Glut 4 (glucose transporter) found?
muscles and adipose tissue
Which glucose transporter regulates insulin?
glut 4
can blood glucose ever be 0?
no
Glut 4 is important to regulate…..
glucose after meals in normal people (insulin regulator)
Glut 2 is important to regulate….
hyperglycemia
What is a competitive inhibitor?
-inhibitor that competes with the substrate for the active site
-competitive inhibitor will have a similar structure to the substrate
-interaction is reversible
How is Km and Vmax affected by a competitive inhibitor?
Km increases, Vmax has no change
Statin drugs are what type of inhibitor? How do they work?
-competitive inhibitor
-statin drugs inhibit HMGCR, which is the key enzyme to making cholesterol (also the rate limiting enzyme)
-so statins are used to decrease cholesterol levels and ultimately prevent heart disease
What is a non-competitive inhibitor?
-interaction is reversible
-inhibitor will NOT compete with the substrate for the active site
-inhibitor will bind elsewhere on the same enzyme
How is Km and Vmax affected with non-competitive inhibitors?
Km has no change, Vmax decreases
What are irreversible inhibitors? What drugs are irreversible inhibitors?
-permanently binds and inactivates the enzyme by covalently modifying it
-toxic chemicals can go this
-some drugs do this like penicillin or aspirin
-aspirin inhibits cyclooxygenase (cox)
What is lineweaver-burke plot?
same thing as MM equation graph but this is a double reciprocal plot
How do competitive and noncompetitive inhibition differ on lineweaver burke plot?
competitive inhibition crosses the enzyme line
noncompetitive inhibition does not cross enzyme line
Enzymes are _________
proteins
T/F: an enzyme speeds up chemical reaction in the cell, but can only be used once
false!
