Characteristics of Enzymes Ms. Dunlap Enzymes Characteristics of Enzymes

DO NOW What 2 harmless products are formed when you react liver homogenate with Hydrogen Peroxide? (Hint: it’s in your notes) T or F: Enzymes will combine with any substrate. Give your reasoning for your answer

Announcement Your Unit 2 test will be Thursday Sept. 4, 2014 and Friday Sept. 5, 2014 respectively depending you’re A/B schedule. I have extended your deadline for your work to Sept. 5, 2014. Everything your are behind on should be online.

Characteristics of Enzymes? speed up chemical reactions are required in minute amounts are highly specific in their action are affected by temperature are affected by pH Some catalyse reversible reactions Some require co-enzymes Are inhibited by inhibitors

(1) Enzymes Speed up chemical reactions Activation Energy with enzyme Activation Energy without enzyme Substrate Products: Energy Time By lowering the activation energy needed to start the reaction.

(2) Enzymes are required in minute amounts Chemically unchanged Sucrase Sucrose Glucose + Fructose They remain chemically unchanged after catalysing the reactions. The same enzyme molecules can be reused over again. Therefore, only a small amount of enzyme is required to catalyse a large number of reactions

(3) Enzymes are highly specific Starch Maltose Amylase Maltose Glucose + Glucose Maltase Each chemical reaction is catalysed by its own specific, unique enzyme. This is due to every enzyme’s specific 3-d configuration. How the shape of an enzyme affects its function can be explained by the “LOCK & KEY HYPOTHESIS”.

Lock & Key Hypothesis Enzymes are proteins and each has an active site. Active sites are depressions on the surface of enzyme molecules with specific shape and specific charges. Active sites are formed due to the way the proteins are folded and held together by H-bonds.

Substrate Enzyme-Substrate Complex Products + Enzyme Active Sites Lock & Key Hypothesis Every active site has it’s own specific shape and charges. It only allows substrates with a COMPLEMENTARY shape and charge to bind with it to form an Enzyme-Substrate Complex Substrate Enzyme-Substrate Complex Products + Enzyme Enzyme

Anabolic Reaction - Synthesis Catabolic Reaction - Hydrolysis

The Lock and Key Hypothesis The substrate binds to a free enzyme with a complementary active site to form the enzyme-substrate complex The enzyme-substrate complex brings about the necessary reactions The product separates from the enzyme, leaving the enzyme molecule unchanged and free to combine again with more substrate molecules

(4) Enzymes are affected by temperature Enzymes can function over a range of temperatures. But all enzymes have their own optimum temperature.

Optimum temperature The optimum temperature is the temperature at which the enzyme is most active, catalysing the largest number of reactions per second. Different enzymes have different optimum temp. Example: most enzymes in the human body functions best at about 37-40oC, near body temperature. Enzymes of thermophilic bacteria that live in hotsprings will have very high optimum temperatures.

How enzyme activity is affected by temperature NOTE: Describe the enzyme activity with respect to the Rate-Temperature Graph Increasing temp up to optimum temp. At low temperature, enzymes are INACTIVE. As temperature rises, the rate of enzyme activity increases (usually 2x as active for every 10oC rise). Enzyme reaching maximum rate of activity at OT Raising the temperature increases the kinetic energy supplied to the substrate and enzyme molecules. This increases the no. of collisions between enzyme and substrate molecules. Increasing the rate of formation of enzyme-substrate complex. Rate of formation of the products increases up till the optimum temperature

How enzyme activity is affected by temperature NOTE: Describe the enzyme activity with respect to the Rate-Temperature Graph Increasing temp beyond optimum temp. Beyond the optimum temperature, rate of enzyme activity deceases. Until it is completely denatured by the extreme heat Increase in temperature increases the vibrations of the atoms in the enzymes. Beyond the OT, the vibrations are so violent that they break the hydrogen bonds that hold the 3-D structrure in place. The enzyme loses its shape and active site The enzyme is DENATURED.

(4) Enzymes are affected by pH Different enzymes have different optimum pH. Enzymes are affected by the acidity or alkalinity of the solutions M indicates the optimum pH when the rate of reaction is the highest

Different enzymes have different optimum pH Examples Enzymes that work best at ACIDIC conditions Renin and Pepsin: Found in the stomach Enzymes that work best at ALKALINE conditions Intestinal Enzymes Enzymes that work best at NEUTRAL conditions Amylase

Different enzymes have different optimum pH

How enzyme activity is affected by pH At pH slightly above or below the optimum Enzyme activity reduces when the conditions are slightly more acidic or alkaline than the optimum pH Slight changes in the pH brings about reversible changes Changes can be restored by bringing enzyme back to the optimum pH

How enzyme activity is affected by pH At extreme pH conditions Enzymes are DENATURED Extreme changes in the pH causes: A change in the charges at the active sites which repels the substrate molecules, preventing them from binding. The irreversible alteration to the bonds that holds the shape of the enzyme. Enzyme thus loses its original 3-D structure. The active site loses its shape.

(5) Some enzymes catalyze reversible reactions D + Reactants Products Products Reactants Some enzymes catalyse both reactions until equilibrium is reached. Reactions will proceed in the direction where the products are constantly being removed E.g formation of glucose during photosynthesis

(6) Some enzymes require co-enzymes Some enzymes require co-enzymes to be bound to them before they can catalyse reactions Co-enzymes Small, non-protein, organic “helper” molecules

(7) Enzymes are inhibited by inhibitors Type 1 (Competitive) Substrate is prevented from binding to active site by inhibitor Type 2 (Non-competitive) Binding of inhibitor does not prevent the binding of substrate but slows down reaction speed