3.6 Enzymes and Chemical Reactions

3.6 IB Objectives 3.6.1 Define enzyme and active site. 3.6.2 Explain enzyme-substrate specificity 3.6.3 Explain the effects of temperature, pH and substrate concentration on enzyme activity. 3.6.4 Define denaturation. 3.6.5 Explain the use of lactase in the production of lactose-free milk.

Chemical Reactions and Enzymes Chemical reactions in living organisms always involve the breaking of bonds in reactants and the formation of new bonds in products. 6H20 + 6CO2 + Light → C6H12O6 + 6O2 Photosynthesis

The Basics Enzymes are a type or class of protein. All proteins are made up of monomers called amino acids. The sequence of amino acids will determine the structure (and function) of the enzyme. Enzymes have complex 3D (globular) shapes. Enzymes act as biological catalysts by altering the rate of chemical reactions without themselves being used up. Enzymes are not considered reactants. Enzymes can speed up metabolic reactions by a factor of 10 million The names of enzymes tend to end in ‘ase’ (catalase, lactase, sucrase) In some reactions, small molecules called coenzymes join with enzymes to control chemical reactions inside cells (ex. Vitamins like B and K).

How Do Enzymes Influence Chemical Reactions Metabolic Reactions: The sum total of all the chemical reactions occurring in the body. Activation Energy: The energy required to get a reaction started Enzymes cannot force reactions to occur that would otherwise not occur. A set of reactions in the presence of an enzyme will form product(s) at a faster rate than those without the enzyme.

The Effects of Enzymes

The Enzyme-Substrate Complex (2 Models) I. The Lock and Key Model:

HYDROLYSIS REACTION

DEHYDRATION SYNTHESIS REACTION

II. The Induced-Fit Model Notice the conformational Change in the active site Of the enzyme. The enzyme’s Active site changes to bring The substrate(s) in Alignment.

Great Enzyme Animations Animation 1 Animation 2 Animation 3

The Effects of Temperature, pH and Substrate Concentration on Enzyme Activity A. Temperature (kinetic energy & molecular collisions):

B. pH (Potential Hydrogen): pH of a solution is dependent on the relative number of hydrogen ions (H+) compared to hydroxide ions (OH-) in the same solution. Pure water has a neutral pH (7) with an equal number of H+ and OH- ions in solution. pH can affect the enzyme-substrate complex (charge matching) or possibly denature the enzyme.

C. Substrate Concentration

Define Denaturation Denaturation, sometimes permanent, is a structural change in a molecule caused by extreme conditions of pH, temperature, etc. In the case of enzymes, a loss of structure results in a loss of function. Denaturation results when intramolecular bonds are stressed and broken.

THE USE OF LACTOSE IN SOLVING THE PROBLEM OF LACTOSE INTOLERANCE

Lactase is obtained from the fungus, Kluyveromyces lactis. Milk is treated with lactase and this breaks down the lactose to the monosaccharides glucose and galactose (which can easily be absorbed by the small intestine). Lactase can be immobilized and the milk passed over it. The prevents the lactase from being in the product (and can be reused). Lactose-free milk is used in the production of ice cream as lactose crystallizes when cold and makes ice cream granular (the glucose and galactose remain dissolved in the ice cream and make it smoother. In yogurt production, bacteria ferment lactose slowly but ferment glucose and galactose—making production faster. Lactose is not as sweet tasting whereas glucose and galactose are. By changing lactose into these two sugars, the products are made sweeter.