Enzymes Flashcards
What kind of enzymes are present in the blood?
Only active enzymes are present; if inactive enzymes are present in the blood, it indicates some kind of pathology
Complex enzymes = __ + __
Protein + non protein part
Protein= apoenzyme (inactive by itself)
Nonprotein if inorganic is considered metal-cofactor
- What is a complete enzyme called?
- Difference and similarity between cosubstrates and prosthetic groups
- Many coenzymes are derived from?
- Holoenzyme (catalytically active)
- Both are coenzymes; cosubstrates are transiently associated and prosthetic groups are permanently associated
- Vitamins
Michaelis menten theory?
Substrate enters the active site (induced fit), substate held in active site by weak interactions, reaction occurs and substrates are converted to products, products are released
- 3 main requirements for a chemical reaction to happen
- What is the transition state?
- What is activation energy?
- Proximity, energy and orientation
- High energy intermediate (very top part on the graph); once you are at the transition state, you know the substrate is going to form a product
- Minimum energy required for reactants to form substrate (energy difference between the reactants and transition state)
Enzymes do what to the activation energy?
Lower activation energy; enzymes do not alter the equilibrium, they just change the rate)
- What kind of relationship do substrate concentration and rate of enzyme catalyzed reaction have?
- Rate increases until Vmax is reached. What does Vmax reflect?
- Direct
2. The saturation of all the available binding sites on the enzyme with the substrate
- What is the michaelis menten equation?
2. What is Km?
- V= Vmax[S] / Km+[S]
- Km is michaelis constant(constant for the enzyme); km= 1/2 Vmax (substrate concentration at 1/2vmax, but it does not vary with the concentration of the enzyme)
What does it mean when you have a small Km?
You need a very small amount of substrate to reach 1/2 vmax (high affinity)
What does the slope of a lineweaver burk plot give you?
Km/Vmax
- What happens in competitive inhibition?
- Kinetics of competitive inhibition: km ___; vmax ___
- How can this kind of inhibition be overcome?
- Inhibitor binds to the same site as substrate binding site (competes with the substrate)
- Km increases (affinity decreases); vmax is unchanged (because there is still the same number of enzymes available to bind with the substrate)
- By increasing substrate concentration
3 common drug types that act as competitive inhibitors?
Antibiotics, anti cancer drugs, and statins
- What happens in noncompetitive inhibition?
- Km ___; vmax ___
- Example of this kind of inhibitor?
- Inhibitor is not competing with the substrate; it binds to a different site
- Km is unchanged (substrate concentration doesnt matter because inhibitor is not binding to the active site); vmax decreases (number of enzymes available to bind with the substrate decreases)
- Heavy metal ions/poisons
- What do allosteric enzymes do?
- Positive effectors vs negative effectors?
- Difference in appearance on a graph compared to michaelis menten curve?
- Bind to site other than active site to cause conformational changes
- Positive - increase catalytic activity of the enzyme; negative- reduce or inhibit catalytic activity
- Michaelis menten = hyperbolic curve; allosteric enzymes = sigmoid curve
What do allosteric effectors do to the Km and Vmax?
Km - alters the affinity of the enzyme for substrate
Vmax- modify the maximal catalytic activity of the enzyme
Suicidal inhibition is irreversible; what does it do?
Name a common drug that is an irreversible inhibitor?
Binds to the enzyme causing a covalent modification to its structure, decreasing the maximum possible concentration of ES complex and vmax
Aspirin
- Name 3 enzymes used for clinical diagnosis of liver disease
- Name 3 enzymes used for clinical diagnosis of acute myocardial infarction
- Alanine transaminase, aspartate transaminase, LDH 5
2. LDH, CK-MB, Troponins
What are isoenzymes?
Physically distinct form of the enzyme that catalyze the same reaction
Creatine kinase (CPK or CK) is an isoenzyme made up of two different polypeptides named?
CK has 3 different isozymes, what are they and what do they indicate?
B and M (for brain and muscle); they make up the dimer
CK1 (BB in brain), CK2 (MB indicates MI), CK3 (MM in skeletal muscle)
How to read lineweaver burk plot:
Y= mx + b
Y axis = ?
X axis = ?
Slope (m) = ?
y intercept (b) = ?
Y axis = 1/V0
X axis = 1/[S]
Slope = Km/Vmax
Y intercept = 1/Vmax
