24 Questions
What is the effect of increasing substrate concentration on enzyme activity?
The velocity of the reaction increases, but then reaches a plateau
What is Km?
The substrate concentration at half-maximal velocity
What happens to Vmax when enzyme concentration is doubled?
It is doubled
What is the relationship between enzyme concentration and the rate of a reaction?
The rate of a reaction is directly proportional to the enzyme concentration
What is the shape of the reaction curve at relatively low concentrations of substrate?
Linear
What is the effect of increasing enzyme concentration on Km?
Km remains the same
What type of kinetics is observed when there is a small increase in V0 with increasing [S]?
Zero-order kinetics
What is the significance of Km?
It is a constant for an enzyme, independent of enzyme concentration
What happens to the velocity of an enzyme reaction when the temperature of the medium is increased?
It increases, reaches a maximum, and then falls
What is the usual optimum pH range for most human enzymes?
Between 6 and 8
What happens to the activity of an enzyme when the temperature is more than 50°C?
It decreases due to heat denaturation
What is the term for the temperature at which the maximum amount of substrate is converted to product per unit time?
Optimum temperature
What happens to the reaction rate in a reversible reaction when the product concentration is increased?
It slows down, stops, or even reverses
What happens to the velocity of an enzyme reaction when the concentration of enzyme is increased, provided substrate concentration is unlimited?
It increases proportionately
What is the term for the process by which the tertiary structure of protein is lost due to high temperature?
Denaturation
What is the effect of pH on the net charge of amino acid residues at the active site?
It influences the net charge
What is the result of an enzyme being activated by certain inorganic ions?
Increased activity
What is the effect of a competitive inhibitor on the Km of an enzyme?
It increases Km
What is the difference between a competitive and non-competitive inhibitor?
Competitive inhibitors bind to the active site, while non-competitive inhibitors bind to a different domain
What is the effect of an increase in substrate concentration on competitive inhibition?
It relieves the inhibition
What is the effect of a non-competitive inhibitor on the Vmax of an enzyme?
It decreases Vmax
What is the mechanism of action of sulfonamide drugs?
They inhibit folic acid synthesis by competitive inhibition
What is the result of converting an inactive pro-enzyme or zymogen to the active enzyme?
Increased enzyme activity
What is the effect of a non-competitive inhibitor on the Km of an enzyme?
It has no effect on Km
Study Notes
Factors Affecting Enzyme Activity
- Substrate concentration:
- Velocity of reaction increases with increasing substrate concentration, initially in a linear relationship, then becoming hyperbolic
- Km (Michaelis constant) is the substrate concentration at half-maximal velocity, representing 50% of enzyme molecules bound to substrate
- Km is independent of enzyme concentration and remains constant for an enzyme
- Enzyme concentration:
- Velocity of reaction increases proportionally with enzyme concentration when sufficient substrate is present
- Temperature:
- Velocity of reaction increases with temperature, reaching a maximum (optimum temperature) and then decreasing
- Most human enzymes have an optimum temperature around 37°C
- pH:
- Each enzyme has an optimum pH, with velocity drastically reduced on either side of the optimum
- pH affects the charge on amino acid residues at the active site, influencing substrate binding and catalytic activity
- Concentration of products:
- In reversible reactions, increased product concentration slows down the reaction rate
- Enzyme activation:
- Certain inorganic ions (e.g., chloride and calcium) can activate enzymes
Enzyme Inhibition
- Competitive inhibition:
- Inhibitor molecules compete with substrate molecules for the active site, reducing available enzyme molecules
- Reversible, with excess substrate abolishing the inhibition
- Increases Km for the substrate, but does not affect Vmax
- Non-competitive inhibition:
- Inhibitor binds to a different domain on the enzyme, reducing enzyme activity
- Irreversible, with no competition between substrate and inhibitor
- Does not affect Km, but decreases Vmax
Pharmacological Applications
- Competitive inhibitors can be used as pharmacological agents, such as sulfonamides, which inhibit folic acid synthesis in bacteria by competing with PABA
This quiz covers the factors affecting enzyme activity and other related concepts from Clinical Biochemistry lectures 10 and 11, as taught by Dr. Naeem Salih Alzaidi.
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