Enzymes Flashcards
(9 cards)
What are enzymes?
Enzymes are proteins that act as biological catalysts by speeding up chemical reactions by lowering the activation energy.
What is the induced-fit model?
Enzymes moulds around the substrate when binding in order to form an ES complex. This weakens specific bonds in the substrate, which lowers the activation energy required for the reaction to happen, increasing the rate of reaction.
What are the factors affecting enzymes?
Temperature, pH, concentration of enzyme and substrate.
How does temperature affect the rate of enzyme-catalysed reactions?
As temperature increases, rate of reaction increases as the enzyme and substrate molecules have more kinetic energy, increasing the frequency of collisions between these molecules, so more enzyme-substrate complexes form.
After the optimum temperature, the rate begins to decrease because the rise in temperature causes the hydrogen and ionic bonds which hold the enzyme’s tertiary structure in place to break, altering the tertiary structure of the enzyme, changing the shape of the active site. This means the shape of the active site is not complementary to the substrate anymore, making the enzyme denatured.
How does pH affect the rate of enzyme-catalysed reactions?
Different enzymes have different optimum pH. As you move away from the optimum pH, rate of reaction decreases because the change in concentration of H+ and OH- ions changes the hydrogen and ionic bonds which hold the enzyme’s tertiary structure in place, altering the tertiary structure of the enzyme, changing the shape of the active site. This means the shape of the active site is not complementary to the substrate anymore, making the enzyme denatured.
How does enzyme concentration affect the rate of enzyme-catalysed reactions?
At first, enzyme concentration is directly proportional to rate of reaction. The more enzymes there are in a solution, the more likely a substrate molecule will collide with one to form an ES complex.
However, after a certain point, the amount of substrate becomes limiting, so increasing the enzyme concentration has no further effect on increasing the rate of reaction, so the rate levels off and remains constant.
How does substrate concentration affect the rate of enzyme-catalysed reactions?
At first, substrate concentration is directly proportional to rate of reaction as the more substrate there is in a solution, the more likely an enzyme is to collide with one and form an ES complex.
After a certain point, the amount of enzymes becomes limiting because all active sites are occupied, and therefore increasing the substrate concentration will have no further effect on increasing the rate of reaction, so the rate levels off and remains constant.
What are competitive inhibitors and how do they decrease the rate of reaction?
Competitive inhibitors are molecules that have a similar shape to the enzyme’s complementary substrate. This means they can fit into the enzyme’s active site to form an enzyme-inhibitor complex. This prevents substrate molecules from binding to the active site.
What are non-competitive inhibitors and how do they decrease the rate of reaction?
Non-competitive inhibitors bind to an enzyme in a place other than the active site (allosteric site). This changes the tertiary structure of the enzyme, altering the shape of the active site too, meaning that it is no longer complementary to that of the substrate. Substrate molecules can therefore no longer bind to the active site.
