EXERCISE 11: Enzymes

Enzymes

- Enzymes are proteins made of long chains of amino acids that form complex shapes -Although cells contain many enzymes, each type of enzyme has a precise structure and function, and each catalyzes a specific reaction.

Enzymes Denaturing

-Any structural change in an enzyme may denature or destroy its effectiveness by altering the active site and slowing down the reaction. -Denatured enzymes may result from extreme temperature, extreme pH, or any environmental condition that fundamentally alters a protein's structure. Therefore, the rate of an enzymatic reaction depends on conditions in the immediate environment. These conditions affect the shape of the enzyme and modify the active site and precise fit of an enzyme and its substrate.

Competitive Inhibition

-Competitive inhibitors are molecules structurally similar to the substrate that compete for a position at the active site of an enzyme. This ties up the enzyme and makes it unable to bind with he substrate. -A high enough concentration of enzyme with a constant concentration of inhibitor will reduce inhibition.

pH Affects the Activity of Enzymes

-Enzymatic activity is sensitive to pH because the surfaces and side groups of enzyme molecules are often charged. -As the pH is lowered, side groups gain H+ ions; as the pH is raised, side groups lose H+ ions. -In this way, solutions having an extreme pH can change an enzyme's conformation enough to alter its active site.

Enzymes

-Enzymes act by binding to reacting molecules, called the substrate, to form an enzyme-substrate complex. -Enzymes lower the activation energy needed to form a transition state.

Activation Energy && Catalysis

-Exergonic reactions (those that release energy) do not necessarily proceed rapidly because energy must be supplied to destabilize existing chemical bonds. This extra energy is the activation energy for the reaction. -Catalysts accelerate particular reactions by lowering the amount of activation energy required to initiate the reaction.

Temperature Affects The Activity of Enzymes

-Heat increases the rate of MOST chemical reactions. -However, higher temperatures do not always accelerate enzymatic reactions; enzymatic reactions have an optimal range of temperatures. Temperatures above or below this range may decrease the reaction rate. -Extreme temperatures often denature enzymes.

Enzymes In Humans

-Most enzymes in humans, such as the protein-degrading enzyme trypsin, work best at temperatures about 40 degrees Celsius and within a pH range of 6 to 8.

Catalase

-The effects of pH can be investigated with catalase, an enzyme in plants and animals that speeds the breakdown of hydrogen peroxide, toxic to cells. -Hydrogen peroxide can act as an oxidizer that denatures macromolecules and kills "germs." -Hydrogen peroxide is broken down by catalase to water and oxygen.

Catechol Oxidase (From Turnip Extract)

-The effects of temperature on enzyme activity can be investigated with catechol oxidase, a plant enzyme that converts catechol to benzoquinone. -When fruit is bruised, injured cells release catechol and catechol oxidase, which react to form a brownish product , benzoquinone. -Toxic to bacteria, benzoquinone prevents decay in damaged cells. -Our source of catechol oxidase was from turnip extract

Activation Energy

-The energy needed to form the transition state is called energy of activation and is lowered by the enzyme.

Active Site

-The site of attachment and the surrounding parts of the enzyme that stress the substrate's bonds constitute the enzyme's active site.

Enzyme-Substrate Complex

-This complex stresses or distorts chemical bonds to form a transition state in which the substrate becomes more reactive and the metabolic reaction accelerates.

Optimal Conditions

The range of values for environmental factors such as temperatures and pH within which an enzyme functions best represents that enzyme's optimal conditions.

Product Formation

The reaction is complete when the product forms and the enzyme is released in its original condition. The enzyme then repeats the process with other molecules of substrate.