Chemical Reactions and

Enzymes

Review

• Living organisms are composed of organic molecules: carbohydrates, lipids, proteins and nucleic acids

• Cellular processes are based on numerous chemical reactions

Chemical Reactions

Chemical Reactions

• During a chemical reaction, one set of chemical is transformed (or changed) into another set of chemicals

Write down the following chemical equation:

CO2 + H2O H2CO3

• In this reaction, carbon dioxide and water react to form carbonic acid

Reactants and Products

• The compounds that enter into a chemical reaction are called the reactants

• The compounds that are produced by a chemical reaction are called the products

Metabolism• The entirety of the chemical reactions

that occur within the cells of a living organism is called metabolism

Metabolic Reactions• Metabolic reactions are grouped into

two general categories: anabolic and catabolic reactions

• During anabolic reactions, simpler substances are combined to form complex molecules

• Energy is absorbed during the reaction• Examples of anabolic reactions include:

protein synthesis and photosynthesis

Anabolic Reactions

• During catabolic reactions, complex molecules are broken down into simpler substances

• Energy is released during the reaction• Examples of catabolic reactions

include: cellular respiration and food digestion

Catabolic Reactions

• Many times, the energy released during a catabolic reaction is used to build molecules during an anabolic reaction

• Metabolic reactions are catalyzed by enzymes

Metabolic Reactions Continued

Enzymes

Enzymes

• Without enzymes, cellular chemical reactions would occur to slowly to sustain the life of the organism

• Most enzymes are found in the cytoplasm of cells, some are found within individual organelles

Enzymes

• Enzymes are proteins that act as organic catalysts to speed up chemical reactions within cells

• As a catalyst, enzymes lower the amount of activation energy required to initiate a chemical reaction

Activation Energy

• Activation energy is the minimum quantity of energy which the reactants must possess in order to undergo a specified reaction

Enzyme-Substrate Complex

• During a chemical reaction, an enzyme binds to a substrate

• The substrate is the reactant that the enzyme will act upon

Enzyme Specificity

• Each enzyme only recognizes a specific substrate and therefore will only catalyze one type of chemical reaction

• For example, the enzyme maltase will only bind to maltose sugar

Enzyme Binding Site

• Only a small part of the enzyme actually binds to the substrate

• This site is called the active site

Lock and Key Model of Enzyme Action

• The enzyme and substrate have complementary shapes

Lock and Key Model of Enzyme Action

Enzyme-Substrate Example

Enzyme Examples

Carbonic anhydrase

Luciferase

Lipase

Helicase

Enzyme Characteristics

Globular Proteins

• Enzymes are globular proteins that act as biological catalysts

• Functional in its tertiary form

Unchanged By Chemical Reactions

• Enzymes do not become “part” of the reaction (unchanged with the exception of the “induced fit theory”)

• Only facilitate the reaction

Enzyme Specificity

• Enzymes are highly specific for their substrate

• Molecular recognition system based on complementary structures (shapes)

Factors That Affect Enzyme

Function

Enzyme Concentration

• An increase in enzyme concentration will increase the rate of the reaction, as long as substrates are available

Substrate Concentration

• An increase in substrateconcentration will increase the rate of the reaction, as long as sufficient enzyme is available

Temperature

• Each enzyme has an optimal temperature for maximum activity

• Temperatures higher than optimal cause enzymes to denature

• Temperatures that are lower than optimal will interfere with enzyme substrate collisions

pH

• Enzymes have optimal pH levels for maximum activity

• Changes in pH may also denature enzymes

• Most enzymes work optimally in neutral conditions, some prefer acidic or alkaline conditions

Enzymes and pH

• Pepsin is an enzyme that functions in the stomach

• Chemotrypsin functions in the small intestine

Activators

• Activators are molecules that bind to enzymes and increase enzyme activity

• Examples of activators include cofactors (inorganic) and coenzymes (organic)

Inhibitors

• Inhibitors are molecules that decrease enzyme activity

• Examples of inhibitors are competitiveand noncompetitive inhibitors (allosteric)

Competitive Inhibitors

• Competitive inhibitors block the substrate from entering the active site on the enzyme

Noncompetitive Inhibitors

• Noncompetitive inhibitors bind to another area on the enzyme and distort the shape of the enzyme, altering the enzyme active site