Topic 3: Enzymes Flashcards
What are the effects of enzymes on chemical reactions?
- Increase reaction date
- Do not alter the equilibrium
- Accelerate attainment of equilibrium
- Decrease activation energy
What is the role of the active site?
Specific region where substrates bind to an enzyme
What are the features of active sites?
- Occupies a small part of the enzyme
- Formed by amino acids from different parts of the primary sequence
- Clefts or crevices
- Have a complementary shape to the substrate
- Bound to enzymes by multiple weak bonds
How do reaction rates vary when substrate concentration changes?
As substrate concentration increases, the rate of reaction increases until max velocity is reached. The leveling off of reaction rate reflects the saturation with substrate of all available binding sites.
How do reaction rates vary when enzyme concentration changes?
Rate of reaction increases if enzyme concentration increases, until there is no substrate available to bind to.
What is the definition of enzyme activity?
Ability of an enzyme to catalyze a specific reaction
What is the definition of a unit of enzyme activity?
Amount of enzyme that produces 1 micro mole of product per min under standard conditions
What is the definition of Km?
- Michaelis constant
- Reflects the affinity of the enzyme for its particular substrate
- Numerically equal to substrate concentration when the reaction velocity is half of a max
- Does not vary with enzyme concentration
What is the definition of Vmax?
Maximal reaction velocity when all catalytic sites on enzyme are saturated with substrate
What does it mean when Km is small?
High affinity of the enzyme for its substrate as a low concentration of substrate is needed to half-saturate the enzyme
What does it mean when Km is large?
Low affinity of enzyme for its substrate as high concentration of substrate is needed to half-saturate the enzyme
What is competitive inhibition?
Inhibitor binds reversible time the same site that the substrate would normally occupy and compete with substrate for that site
What is the effect of a competitive inhibitor on Vmax?
Unchanged: by increasing the concentration of substrate, the reaction will still reach the same Vmax
What is the effect of a competitive inhibitor on Km?
In the presence of a competitive inhibitor, more substrate is needed to achieve half Vmax, hence increasing Km.
What is non-competitive inhibition?
Inhibitor and substrate bind at different sites on the enzyme, decreasing the concentration of functional enzyme
