Enzymes INB Pg 20

 Enzymes are protein molecules that act as biological catalysts  Catalyst: molecule that speeds up a chemical reaction and remains unchanged after rxn  Enzymes usually end in –ase  Virtually every metabolic rxn is catalyzed by an enzyme Enzymes

 Globular proteins  Precise 3D shape  Multiple chains  Hydrophilic R groups on outside = water soluble  Active site: region on an enzyme to which another molecule/molecules- called a substrate- can bind Enzymes

 Idea that enzyme has a particular shape to which the substrate fits exactly  Substrate=key. Held in place by temporary bonds  Enzyme=lock Lock and Key Hypothesis

 Each type of enzyme will act on only one type of substrate molecule  Shape of active site will only allow one shape to fit  Enzyme is said to be specific for substrate Lock and Key Hypothesis

 Modified the lock and key hypothesis in 1959  New evidence suggested that enzymes are more flexible than is suggested by a rigid lock and key  Basically same as lock and key, but adds the idea that the enzyme, and sometimes substrate, changes shape slightly as substrate enters enzyme Induced Fit Hypothesis

 Ensures a more perfect fit  Makes catalysis more efficient  Induced Fit Hypothesis

 An enzyme may catalyze a reaction in which it joins together two peptides (synthesis)  An enzyme may catalyze a reaction in which the substrate molecule is split into two or more molecules (catalysis/decomposition) Catalysis and synthesis

 Enzyme-product complex is briefly formed before the release of products  Interaction between the R groups of the enzyme and the atoms of the substrate can break, or encourage formation of, bonds in the substrate molecule, forming products  When the rxn is complete, the products leave the active site  Enzyme is unchanged and ready to accept another substrate  Rate of rxn is extremely rapid Catalysis

 Found in tears, saliva, and other secretions. Breaks the polysaccharide chains in the cell walls of bacteria Lysozyme

 As catalysts, enzymes increase the rate at which chemical reactions occur  Most of the rxns in living things would be too slow w/o an enzyme to sustain life Enzymes

 Energy needed to start reaction = activation energy  Enzymes work by lowering activation energy Chemical Reactions

 Increase concentration of substrate  Increase energy of reactants (heating)  Ex: Benedict’s test  Most rxns occur at temps higher than our body temp, which is why enzymes are necessary Other ways to increase rxn rate

 When enzyme and substrate are first mixed, there are a large number of substrate molecules  At any moment, virtually every enzyme molecule has a substrate in its active site The course of a reaction

 Initially, the rate at which a reaction occurs will depend only on how many enzyme molecules there are and the speed at which the enzyme can convert substrate into product  However, as more substrate is converted to product, there are fewer and fewer substrate molecules, which slows down the rate of reaction The course of a reaction

 Directly proportional to reaction rate  As we increase the concentration of an enzyme, we have more active sites available for the substrate.  As long as there is plenty of substrate available, the initial rate of reaction increases linearly with enzyme concentration The effect of enzyme concentration

 As concentration of substrate increases, the initial rate also increases  If we continue increasing substrate concentration, it will eventually max out because there are no more available active sites  If more substrate is added, the enzyme simply cannot work faster. The enzyme is working at its maximum possible rate, known as V max (V=velocity) The effect of substrate concentration

 Low temp=low particle movement. Substrate move very slowly and will not often collide with the active site  As temp increases, substrates move faster and collide with active site more. Reaction rate increases  At a certain temperature (specific for diff. enzymes), hydrogen bonds begin to break in the enzyme (remember, it is a protein) and the enzyme will denature (loose its structure and function) Temperature and enzyme activity

 Denaturing of an enzyme is often irreversible  Substrate cannot fit into denatured active sites, so no activity takes place  The temperature at which an enzyme catalyzes a reaction at the maximum rate is called the optimum temperature Temperature and enzyme activity

 pH is a measure of hydrogen ions in solution. The lower the pH, the higher the hydrogen ion solution.  Hydrogen can interact with R groups of amino acids which affects bonding in amino acids, which can change the structure (and function) of an enzyme  Enzymes work best under specific pH ranges. pH and enzyme activity

 Proteases (enzymes that break down proteins) are used in biological washing powders.  How would a protease remove a blood stain on clothes?  Most biological washing powders are recommended for use at low washing temperature. Why is this? Check your understanding

 Hemoglobin is the colored pigment that causes blood stains. Protein-digesting enzymes hydrolyze hemoglobin to amino acids, which are colorless. They are also soluble, so will wash away in water.  Many protein-digesting enzymes have an optimum temperature of around 40 °C. If the temperature of a reaction is too high, the enzyme will denature. Check your understanding