Enzymes Flashcards
What is activation energy?
The minimum amount of energy needed to activate a reaction
What effect do enzymes have on activation energy
Enzymes lower activation energy
Name the molecule that an enzyme acts on
Substrate
Where on an enzyme does a substrate bind?
Active site
What does an enzyme and substrate form when they bind together?
Enzyme-substrate complex (ES complex)
Name two theories of enzyme action
Lock and key hypothesis
Induced fit hypothesis
Explain the lock and key hypothesis
The substrate is the key, the enzymes active site is the lock. The substrate fits into the active site of the enzyme as it is complementary in shape
Name a key difference between the lock and key hypothesis and the induced fit hypothesis
The enzymes active site changes shape in the induced fit hypothesis, whereas the shape of the active site remains the same in the lock and key hypothesis
What biological molecule are enzymes?
Proteins
What is meant by a biological catalyst?
Enzymes - speed up the rate of reaction in living organisms
Why are enzymes effective in small quantities?
They can be used over and over again
Name 4 factors that affect the rate of an enzyme controlled reaction
- Temperature
- pH
- Concentration of enzyme
- Concentration of substrate
DESCRIBE the effect of temperature on an enzyme controlled reaction
Rate of reaction increases, peaks, then decreases
EXPLAIN the effect of temperature on an enzyme controlled reaction
Increasing temperature increases the kinetic energy of molecules so more enzyme-substrate collisions occur. More enzyme substrate complexes (ES complexes) form.
Above optimum temperatures, the enzyme denatures (shape of the active site changes irreversibly), less or no ES complexes form
DESCRIBE the effect of pH on an enzyme controlled reaction
Rate of reaction increases, peaks, and then decreases
EXPLAIN the effect of temperature on an enzyme controlled reaction
pH alters the charges on amino acids that make up the active site. The active site is no longer complementary in shape to the substrate - the enzyme has denatured
DESCRIBE the effect of substrate concentration on an enzyme controlled reaction
As the substrate concentration increases so does the rate of reaction up to a point when the rate of reaction plateaus
EXPLAIN the effect of substrate concentration on an enzyme controlled reaction
As the substrate concentration increases, more substrate molecules are available to collide with an enzymes active site forming ES complexes.
The rate of reaction becomes limited by the concentration of enzyme as the enzymes are working at maximum capacity when the graph plateaus
What is meant by the maximum capacity/turnover of an enzyme?
The maximum rate at which all the enzymes can work
What is pH a measure of?
The hydrogen ion concentration
Explain why enzymes work less well at lower temperatures?
Lower temperatures reduce the amount of kinetic energy which results in less collisions and less ES complexes
Explain why high temperatures may prevent enzymes from functioning
High temperatures denature enzymes - alter the shape of the active site irreversibly
What is meant by the induced fit hypothesis?
Binding of the substrate changes the shape of the enzymes active site, making the enzyme able to react.
The enzymes active site returns to its original shape once the products have been released
Name two types of inhibitors
Competitive and non-competitive
Explain how competitive inhibitors work
Competitive inhibitors are molecules that are complementary in shape to an enzymes active site.
They compete with substrate molecules for the active site
Explain how non-competitive inhibitors work
Non competitive inhibitors bind to a site other than the active site on an enzyme (allosteric site).
This produces a change in the shape of the active site so substrate molecules can no longer bind
What effect do competitive inhibitors have on the rate of an enzyme controlled reaction?
Rate of reaction is slower, maximum rate of reaction can be achieved depending on the concentration of the inhibitor
What effect do non-competitive inhibitors have on the rate of an enzyme controlled reaction?
Non-competitive inhibitors reduce the rate of reaction. The maximum rate of reaction is not reached as the change in the shape of the active site is permanent
