Presentation on theme: "Enzyme Activity The properties of enzymes related to their tertiary structure.The effects of change in temperature,pH,substrate concentration,and competitive."— Presentation transcript:
Enzyme Activity The properties of enzymes related to their tertiary structure.The effects of change in temperature,pH,substrate concentration,and competitive and non-competitive inhibition on the rate of enzyme action
HOW ENZYMES WORK Enzymes are ORGANIC CATALYSTS. A CATALYST is anything that speeds up a chemical reaction that is occurring slowly. How does a catalyst work? The explanation of what happens lies in the fact that most chemical reactions that RELEASE ENERGY (exothermic reactions) require an INPUT of some energy to get them going. The initial input of energy is called the ACTIVATION ENERGY
Enzymes An enzyme is a biological catalyst The pockets formed by tertiary and quaternary structure can hold specific substances (SUBSTRATES). These pockets are called ACTIVE SITES. When all the proper substrates are nestled in a particular enzyme's active sites, the enzyme can cause them to react quickly Once the reaction is complete, the enzyme releases the finished products and goes back to work on more substrate.
Properties of Enzymes relating to their tertiary structure. The activity of enzymes is strongly affected by changes in pH and temperature. Each enzyme works best at a certain pH and temperature,its activity decreasing at values above and below that point. This is because of the importance of tertiary structure (i.e. shape) in enzyme function and forces, e.g., ionic interactions and hydrogen bonds, in determining that shape.
The effects of change in temperature. Temperature: enzymes work best at an optimum temperature. Below this, an increase in temperature provides more kinetic energy to the molecules involved. The numbers of collisions between enzyme and substrate will increase so the rate will too. Above the optimum temperature, and the enzymes are denatured. Bonds holding the structure together will be broken and the active site loses its shape and will no longer work
The effect of change in pH. pH: as with temperature, enzymes have an optimum pH. If the pH changes much from the optimum, the chemical nature of the amino acids can change. This may result in a change in the bonds and so the tertiary structure may break down. The active site will be disrupted and the enzyme will be denatured.
The effect of change in concentration Enzyme concentration: at low enzyme concentration there is great competition for the active sites and the rate of reaction is low. As the enzyme concentration increases, there are more active sites and the reaction can proceed at a faster rate. Eventually, increasing the enzyme concentration beyond a certain point has no effect because the substrate concentration becomes the limiting factor. Substrate concentration: at a low substrate concentration there are many active sites that are not occupied. This means that the reaction rate is low. When more substrate molecules are added, more enzyme- substrate complexes can be formed. As there are more active sites, and the rate of reaction increases. Eventually, increasing the substrate concentration yet further will have no effect. The active sites will be saturated so no more enzyme-substrate complexes can be formed.
Competitive and non-competitive inhibition Inhibitors slow down the rate of a reaction. Sometimes this is a necessary way of making sure that the reaction does not proceed too fast, at other times, it is undesirable Reversible inhibitors: Inhibitors Competitive reversible inhibitors: these molecules have a similar structure to the actual substrate and so will bind temporarily with the active site. The rate of reaction will be closer to the maximum when there is more real substrate, (e.g. arabinose competes with glucose for the active sites on glucose oxidase enzyme). Non-competitive reversible inhibitors: these molecules are not necessarily anything like the substrate in shape. They bind with the enzyme, but not at the active site. This binding does change the shape of the enzyme though, so the reaction rate decreases.
Irreversible inhibitors: These molecules bind permanently with the enzyme molecule and so effectively reduce the enzyme concentration, thus limiting the rate of reaction, for example, cyanide irreversibly inhibits the enzyme cytochrome oxidase found in the electron transport chain used in respiration. If this cannot be used, death will occur