biology4alevel600

1  Enzymes are globular proteins which catalyse metabolic reactions. 2  Each enzyme has an active site with a specific shape, into which the substrate molecule or molecules fit precisely. This is the lock and key hypothesis – the substrate is compared with a key which fits precisely into the lock of the enzyme. 3  The lock and key hypothesis has been modified. The modern hypothesis is called the induced fit hypothesis. The active site is no longer regarded as a rigid structure like a lock, but as a flexible structure which can change shape slightly to fit precisely the substrate molecule. 4  When the substrate enters the active site, an enzyme–substrate complex is temporarily formed in which the R groups of the amino acids in the enzyme hold the substrate in place. 5  Enzymes may be involved in reactions which break down molecules or join molecules together. 6  Enzymes work by lowering the activation energy of the reactions they catalyse. 7  The course...

Michaelis-Menten equation describes  the  velocity of enzymatic reactions (v)  by relating it to [S] -  concentration of a substrate   S . Michaelis - Menten Equation An example curve with parameters V max  = 3.4 and  K m  = 0.4. Wikipedia.  Here, V max  represents the maximum rate achieved by the system, at maximum (saturating) substrate concentrations. The Michaelis constant K m  is the substrate concentration at which the reaction rate is half of V max . K m   is (roughly) an  inverse  measure of the  affinity  or strength of binding between the enzyme and its substrate. The lower the K m , the greater the affinity (so the lower the concentration of substrate needed to achieve a given rate). It permits prediction of whether or not the rate of formation of product will be affected by the availability of substrate. ucl.ac.uk Immobilising an enzyme in alginate   • In industry  enzymes are...

These factors are: - Temperature - pH - Enzyme concentration - Substrate concentration   - Inhibitor concentration When an enzyme solution is added to a solution of its substrate , the molecules collide .  With time, the quantity of substrate ↓(changed into product) --> frequency of collisions ↓--> rate of reaction gradually ↓.  The reaction rate is fastest at the start of the reaction (substrate concentration is greatest). --> When comparing reaction rates of an enzyme in different circumstances, we should measure the initial rate of reaction. 1. Temperature As  t o  ↑, kinetic energy of reacting molecules ↑--> ↑ successful collision --> ↑ rate of reaction.  At optimal  t o enzyme's activity is maximal --> rate is maximal. Above this temperature, H bonds holding enzyme molecule in shape begin to break --> change tertiary structure of the enzyme (denaturation) --> active site is deformed ---...

Measurement of the rate of formation of the product or the rate of disappearance of the substrate . 1. Measurement of the rate of formation of  O 2  in the reaction: Mash up some biological material like potato tuber or celery stalks, mix them with water and filter the mixture to obtain a solution containing catalases .  Add the mixture to H 2 O 2   (hydrogen peroxide) in a test tube. Use small tubes --> not too much gas in the tube above the liquid.  Collect the gas in a gas syringe and recording the volume every minute until the reaction stops. Note - You can replace the gas syringe by an inverted measuring cylinder over water. 2. Measurement of the rate of disappearance of starch in the reaction: Add amylase solution to starch suspension in a test-tube.  Take samples of the reacting mixture at regular time intervals, and test for the presence of starch using iodine in KI solution.  When starch is present , iodine is dark blue. If the ...