Flashcards in Brar - Enzymes, Enzyme Kinetics Deck (39):
What do and don't enzymes do?
Catalyze specific biochemical reactions
DO NOT create new reactions.
List 4 general areas where enzymes are needed as catalysts.
Mitochondrion, cytosolic, lysosomal, and nuclear areas.
How do enzymes catalyze reactions?
They are specific and reduce the activation energy required for the reaction to occur.
Can enzymes be used more than once?
Yes, they are not destroyed and return to their original state after rxn.
What occurs in an enzyme's active site?
an enzyme-substrate complex is formed and the site contains functional groups that help in rxns
What are the 2 substrate binding models?
Lock and key model
Induced fit model
Describe the Lock and key model.
fixed and rigid model; small differences in structure can prevent proper binding
Describe the Induced Fit model.
flexible 3-D structure that undergoes conformational change when substrate binds and exposes more residues.
What is the transition state complex?
maximum energy level reached during a rxn; it is unstable and decomposes to products
What is activation energy?
the difference in energy between the substrate and the transition state complex
Which amino acid is one of the more important functional groups of an active site?
Serine-OH in proteases
What effects does pH have on enzyme catalysis?
it can denature the enzyme, decrease its function the farther away from it's ideal pH level, or change its function based on the pH level
What are 2 mechanism based inhibitors?
Covalent inhibitors and Transition State Analogs
How do covalent inhibitors work?
covalently bind to residues in active site and renders enzyme useless or dead
Is a covalent inhibition reversible?
No, it is irreversible.
List some examples of covalent inhibitors? What enzyme do they inhibit?
Sarin, malathion, and parathion (pesticides).
What are transition state analogs?
Irreversible inhibitors sometimes termed “suicide inhibitors” that reduce/eliminate an enzyme's function
List some examples of transition state analogs and the enzymes they inhibit.
Penicillin → Glycopeptidyl transferase (GPT)
Allopurinol → Xanthine oxidase
What is Allopurinol used to treat?
Gout by decreasing urate porduction
What enzymatic reactions do Oxidoreductases catalyze?
Lactate ↔ Pyruvate (Lactate dehydrogenase)
What do Transferases catalyze?
transfer of C-, N-, or P- containing groups.
Serine ↔ Glycine (Serine hydroxy-methyl transferase
What do Hydrolases catalyze?
cleavage of bonds by adding H20.
Urea → CO2 + 2 NH3 (Urease)
What do Lyases catalyze?
cleavage of C-C, C-S, and certain C-N bonds.
Pyruvate → Acetaldehyde (Pyruvate decarboxylase)
What do Isomerases catalyze?
racemization of optical or geometric isomers.
Methylmalonyl CoA ↔ Succinyl CoA (Methylmalonyl CoA mutase)
What do Ligases catalyze?
formation of bonds btwn C and O, S, or N coupled to hydrolysis of high energy phosphates.
Pyruvate → Oxaloacetate (Pyruvate carboxylase)
As substrate concentration increases, what else increases?
the velocity (V) of the reaction
How much or how long will the velocity increase?
until the enzyme is saturated; this point is known as Vmax
What is Km and what is it also known as?
the minimum substrate concentration required for effective catalysis to occur; Michaelis Menten constant
What two parts of the reaction below determine the rate of reaction?
E + S ↔ ES → E + P
concentration of ES and k2
Name the following equation
V = ---------------
Km + [S]
the Michaelis Menten (MM) equation
What is the Km value a reflection of?
an enzymes affinity for its substrate; low Km = high affinity
If the Km value is high, what does that mean?
the enzyme has a low affinity for its substrate therefore a higher substrate concentration is needed
What does the turnover number (kcat) measure?
it directly measures the rate of the catalytic process and it is used instead of k2 in multi-step rxns
What can the kcat value also be thought as?
What does the ratio of kcat/Km measure?
it conveniently measures enzyme efficiency
What is the most efficient enzyme in the world?
What factors affect the reaction velocity?
Substrate concentration, temperature, and pH
What does Michaelis Menten enzyme and allosteric enzyme activity look like on a graph?
MM enzymes follow a hyperbolic curve
Allosteric enzymes follow a sigmoid curve