Overview of Enzymes Flashcards
What is the main function of enzymes?
Lower the activation energy (EA) for a reaction.
Enzymes are biological catalysts. What is the significance of this?
Enzymes increase reaction rates which increases the amount of product formed per unit of time.
What are substrates?
Reactants acted upon by enzymes.
What is the active site of an enzyme?
Location where the substrate binds.
What is enzyme specificity?
The active site of an enzyme only binds a specific substrate.
What is an enzyme-substrate complex?
A complex formed when an enzyme and substrate bind tightly together.
What is activation energy?
The minimum amount of energy needed to start a chemical reaction.
Why is it so important for enzymes to lower activation energy (EA)?
Because it decreases the barrier for starting a reaction.
(If the energy barrier is lower, then the enzyme can catalyze the reaction much faster, thus increasing reaction rate.)
What does the induced fit model state?
A substrate binds to an enzyme and induces a conformational change in its active site, so that they are a complementary fit.
What are cofactors?
Inorganic molecules (or metal ions)
Example: minerals
What are coenzymes?
Organic molecules
Example: vitamins or vitamin derivatives
What is the main function of both cofactors and coenzymes?
Activate enzymes by inducing conformational changes.
What is a holoenzyme? Apoenzyme?
holoenzyme: An enzyme WITH its cofactor
apoenzyme: An enzyme WITHOUT its cofactor
(completely nonfunctional)
What is a zymogen?
An inactive form of an enzyme.
What is Vmax?
How fast an enzyme can catalyze a reaction.
(the rate of reaction when the enzyme is saturated with substrate)
What is Km (or Michaelis constant)?
Substrate concentration at which the reaction rate is equal to 1/2Vmax.
(Km = 1/2Vmax)
When does saturation kinetics occur?
When Vmax has been reached.
Adding more substrate will NOT increase reaction rate, once Vmax has been reached.
A low Km, has what kind of substrate affinity?
low Km = high substrate affinity
A high Km, has what kind of substrate affinity?
high Km = low substrate affinity
What is Km inversely proportional to?
Enzyme-substrate affinity
What are the three main factors that affect the rates of enzymes?
- temperature
- pH
- salinity (increasing levels of salt can disrupt hydrogen and ionic bonds)
What is the optimal temperature for enzymes in the human body?
37° C
[37°C = 98.6°F = 310 K]
When does an enzyme or protein exhibit cooperativity?
When there are multiple binding sites or subunits.
Cooperativity results in a sigmoidal shape curve (s-shape).
What is the Hill coefficient (nH)?
A measure of the cooperativity of substrate binding to an enzyme.
For the Hill coefficient (nH), what does it mean if:
- nH = 0
- nH > 1
- nH < 1
- nH = 0 NO cooperativity
- The enzyme follows normal M-M kinetics.
- nH > 1 positive cooperativity
- i.e. hemoglobin binding with oxygen
- nH < 1 negative cooperativity
- If it’s essentially one ( such as 1.1, or 1.2) it is still considered negative cooperativity.
What is an endergonic (or nonspontaneous) reaction?
A reaction that requires energy input.
ΔG > 0
What is an exergonic (or spontaneous) reaction?
A reaction that releases energy.
ΔG < 0
What occurs when a homogenous catalyst is not separated from products at the end of a reaction?
The products will be contaminated.
How will the rate of a catalyzed reaction be affected if the solid catalyst is finely ground before being added to the reaction mixture?
The rate will be faster because a greater surface area of catalyst will be exposed.
