Enzymes Flashcards
What type of proteins are enzymes?
Enzymes are globular proteins.
What are intracellular enzymes?
Intracellular enzymes are enzymes that catalyze reactions inside cells.
What are extracellular enzymes?
Extracellular enzymes are enzymes that are secreted by cells and catalyze reactions outside cells.
What does the lock and key hypothesis state?
The lock and key hypothesis states that the substrate is a complementary shape to the enzyme’s active site and fits exactly, showing specificity.
What does the induced fit hypothesis state?
The induced fit hypothesis states that the substrate is complementary to the active site but not an exact fit. The enzyme or substrate slightly changes shape to ensure a perfect fit while still showing specificity.
How do enzymes interact with water?
Enzymes have hydrophilic R groups on their outer surface, making them soluble in water in the cytoplasm.
How do enzymes affect activation energy?
Enzymes lower the activation energy of reactions they catalyze.
Explain how the rate of a reaction changes over time.
When the enzyme and substrate are first mixed, there are a large number of substrate molecules. At any moment, almost every enzyme molecule has a substrate molecule in its active site. However, as more and more substrate is converted into product, there are fewer and fewer substrate molecules to bind with enzymes. Enzyme molecules may be waiting for substrate molecules to hit their active sites. As fewer and fewer substrate molecules are left, the reaction gets slower and slower until it eventually stops.
Explain the effect of temperature on the rate of enzyme activity.
At low temperatures, the rate of reaction is slow. The kinetic energy of the molecules is low and the molecules are moving slowly. Substrate molecules will not often collide with the active site of the enzyme. As temperature increases, the kinetic energy of the molecules increases and so the enzyme and substrate molecules move faster. Collisions happen more frequently and with more energy and the substrate molecules enter the active site more often. However, above a certain temperature, the enzyme molecule vibrates so much that some of the bonds holding the enzyme molecule in its precise shape begin to break. The enzyme’s active site begins to lose its shape and therefore its activity. It is said to be denatured. At first, the substrate molecule fits less well into the active site of the enzyme so the rate of the reaction begins to slow down. Eventually, the substrate no longer fits at all and the reaction stops. The rate becomes zero.
Explain the effect of pH on the rate of enzyme activity.
Hydrogen ions are positively charged, so they are attracted to negatively charged ions and repelled by positively charged ions. Hydrogen ions can therefore interact with any charged R groups on the amino acids of enzyme molecules. This may break the ionic bonding between the R groups, which affects the three-dimensional structure of the enzyme molecule. The shape of the active site may change and therefore reduce the chances of the substrate molecule fitting into it. A pH which is different from the optimum pH can cause denaturation of an enzyme.
Which solution can we use to maintain the pH of a reaction?
Buffer solution.
Explain the effect of enzyme concentration on the rate of enzyme activity.
Reaction rate is directly proportional to the enzyme concentration. The more enzyme present, the more active sites will be available for the substrate to fit into.
Explain the effect of substrate concentration on the rate of enzyme activity.
As substrate concentration increases, the initial rate of reaction also increases. There are increased collisions between the substrate and the active site of the enzyme. The more substrate molecules there are, the more often one will enter an active site. However, if you go on increasing substrate concentration, keeping the enzyme concentration constant, there comes a point when every enzyme active site is full. If more substrate is added, the enzyme simply cannot work faster. Substrate molecules are effectively queuing up for an active site to become vacant. At lower concentration, more active sites are available. At higher concentration, active sites become saturated.
What is the Km value?
The substrate concentration at which an enzyme works at half its maximum rate. The lower the value of Km, the more efficient the enzyme. Higher the affinity of an enzyme for its substrate, the lower the substrate concentration needed before half Vmax is reached. The lower the substrate concentration, the lower the value of Km. So, the higher the affinity of an enzyme for its substrate, the lower its Km will be.
Explain competitive inhibition.
When a substrate reduces the rate of activity of an enzyme by competing with the substrate molecules by the enzyme’s active site, increasing substrate concentration reduces the degree of inhibition. Increasing inhibitor concentration increases the degree of inhibition.
Explain non-competitive inhibition.
When a substance reduces the rate of activity of an enzyme, but increasing the concentration of the substrate does not reduce the degree of inhibition, many non-competitive inhibitors bind to areas of the enzyme molecule other than the active site itself.
State the advantages of using immobilised enzymes.
- can keep and reuse the enzymes and that the product is enzyme-free.
- are more tolerant of temperature changes and pH changes than enzymes in solution.
What is the formula to calculate the rate of a reaction?
Rate=Appearance of products/disappearance of reactants divided by time
