Biology: Enzyme Flashcards
What is the Lock and Key method?
States that enzyme’s active site is complementary to the substrate molecule. The active site is like a lock and the substrate is like a key fitting perfectly into the lock. The shape and properties of the active site are given by the amino acids around it. These amino acids form weak hydrogen and ionic bonds with the substrate molecule, so the active site binds one substrate only. The formulation of enzymes substrate complexes lowers the activation energy to catalyse the reaction.
What is the Induced Fit Model?
States that the enzyme is flexible and so the active site can change shape. The active site isn’t exactly complementary to the substrate, but as the bind, the active site changes shape to fit the substrate more closely. The change in turn distorts the substrate molecule in the active site, making it more likely to change into the product. For example if a bond in the substrate is to be broken, the bond might be stretched by the enzyme, making it more likely to break. Alternatively if a bond is to be made between two molecules, the two molecules can be held in exactly the right position and orientation and “pushed” together, Making the bond more likely to form. The activation energy is therefore lowered. The enzyme can also make the local conditions inside the active site quite different from those outside (such as pH, water concentration, charge), so that the reaction is more likely to happen. the Induced Fit Model explains the action of enzymes more fully that the lock and key model.
Factors that Affect the Rate of Enzyme Controlled Reactions: Substrate Concentration
Increasing the substrate concentration increase the rate of reaction because there is more chance of collisions between the enzyme’s active site and the substrate so a greater number substrate complexes from.
The rate does not increase with further increases in substrate concentration because the number of enzymes is a limiting factor. At any one moment in time all the enzyme’s active sites are occupied/saturated.
Factors that Affect the Rate of Enzyme Controlled Reactions: Temperature
An increases in temperature the kinetic energy of the molecules so there is a greater chance of collisions occurring between the enzyme’s active site and the substrate. A greater number of enzymes substrate complexes form.
A high temperature the enzyme denature because the hydrogen bonds in the tertiary and secondary structure break so the enzyme loses its tertiary structure. The active site changes shape and is no longer complementary to the substrate. Enzyme substrate complexes cannot form.
Factors that Affect the Rate of Enzyme Controlled Reactions: pH
At pH values than the optimum the greater number of H+ions changes the charge of the enzyme (changes the charge of the ionic R groups which causes bonds to break). THe lower the pH the greater the number of enzymes that denature (tertiary structure). The enzyme’s active sites are no longer complementary to the substrates so fewer enzyme substrate complexes form. At higher pHs it is the lack of H+ ions it the greater number of OH- ions that causes the loss of the tertiary structure.
Factors that Affect the Rate of Enzyme Controlled Reactions: Competitive Inhibitors
Competitive Inhibitors have a similar shape to the substrate and are able to bind to the active site. The greater the number of inhibitors then the lower the chance of collisions between the substrate and the active site so the lower the number of enzyme substrate complexes.
At higher substrate concentrations there is a greater chance of the substrate binding with the active site than the inhibitor so the number of enzyme substrate complexes forming is higher.
Factors that Affect the Rate of Enzyme Controlled Reactions: Non-competitive Inhibitors
Non-Competitive inhibitors are not complementary to the active site. They bind to a different location on the enzyme. It is no longer complementary to the substrate so fewer enzyme substrate complexes form. Increasing the substrate concentration does not lead to increases in rate back to the level that there is without the substrate.
How can measuring how fast the product is made tell us the rate of an enzyme-controlled reaction?
How fast the product I made - by measuring the amount of end product there is present at different times i.e. the volume of the gas produced or the time it takes for a colour change due to the product to occur
How can measuring how fast the substrate is made tell us the rate of an enzyme-controlled reaction?
How fast the substrate is made - by measuring how much substrate is left at different times i.e. the size of a clear zone around a well of enzyme in agar plates or time iit teks for a cloudy solution to be clear because there is no substrate remaining.
What is the rate of reaction?
The rate of reaction in other words is the speed that a chemical reaction is going at. Remembering the formula for calculating speed can help your work out the formula for calculating the rate of a reaction. Speed = distance divided by time (for example we measure the distance a person has ran and then divide by the time it took them.) The rule for the (speed) rate of reaction then is divide whatever has be measured by the time it took.
Example of Rate of Reaction?
Experiment:
Liver was added to different concentrations of hydrogen peroxide. Catalase in the liver catalyses the breakdown of hydrogen peroxide into oxygen and water. The volume of oxygen procured over 50 sec was measured.
Formula for Calculating Rate of Reaction:
Volume of oxygen produced
—————————————–
time
Units:
cm^3s^-1
