Agenda Attendance Review chart of mutations Enzyme interactive website Notes Practice Tooth pick activity

Enzymes and Metabolism!!! Lets speed up some reactions!!

Vocab you need to know by the end of this Unit Vocabulary: activation energy, biochemical reaction, coenzyme, competitive inhibitor, enzyme, enzyme activity, enzyme concentration, heavy metal, induced fit model, metabolism, non-competitive inhibitor, pH, proteins, substrate, substrate concentration, thyroid, thyroxin, vitamins

First you need to know: What are acids? What are bases? What are buffers? Why do we Care?

Acids are molecules that release hydrogen ions in solution. HCl  H+ + Cl- A strong acid, such as hydrochloric acid, dissociates completely.

Bases are molecules that either take up hydrogen ions or give off hydroxide ions in solution. NaOH  Na+ + OH-

Concentrations of hydrogen ions or hydroxide ions can be represented using the pH scale. moles/liter 1 x 10 –6 [H+] = pH 6 1 x 10 –7 [H+] = pH 7 1 x 10 –8 [H+] = pH 8 As we move down the scale from pH 7 to pH 6, there are 10X more hydrogen ions.

Buffers are substances that help to resist change in pH. When more hydrogen ion is added, the reaction shifts to the left and more carbonic acid is formed. When hydroxide ions are added, the reaction shifts to the right and bicarbonate and water are formed.

Describe the importance of pH to biological systems in the human body.

Metabolic Reactions and Energy Transformations Metabolism is the sum of all the chemical reactions that occur in a cell. Reactants are substances that participate in a reaction; products are substances that form as a result of a reaction. A reaction will occur spontaneously if it increases entropy. Biologists use the term “free energy” instead of entropy for cells.

Free energy, G, is the amount of energy to do work after a reaction has occurred. ΔG (change in free energy) is calculated by subtracting the free energy of reactants from that of products. A negative ΔG means the products have less free energy than the reactants, and the reaction will occur spontaneously. Free energy, denoted by G, is named for Josiah Gibbs who first developed the concept.

Exergonic reactions have a negative ΔG and energy is released. Endergonic reactions have a positive ΔG and occur only if there is an input of energy. Energy released from exergonic reactions is used to drive endergonic reactions inside cells. ATP is the energy carrier between exergonic and endergonic reactions.

ATP: Energy for Cells ATP (adenosine triphosphate) is the energy currency of cells. ATP is constantly regenerated from ADP (adenosine diphosphate) after energy is expended by the cell. ATP is coupled to endergonic reactions in such a way that it minimizes energy loss.

ATP is a nucleotide made of adenine and ribose and three phosphate groups. ATP is called a “high-energy” compound because a phosphate group is easily removed. The amount of energy released when ATP is hydrolyized is 7.3 kcal per mole.

The ATP cycle In cells, the exergonic breakdown of glucose is coupled to the buildup of ATP, and then the exergonic breakdown of ATP is coupled to endergonic reactions in cells. When a phosphate group is removed by hydrolysis, ATP releases the appropriate amount of energy for most metabolic reactions. The high-energy content of ATP comes from the complex interaction of the atoms within the molecule.

Coupled Reactions In coupled reactions, energy released by an exergonic reaction drives an endergonic reaction.

Coupled reactions The breakdown of ATP is exergonic. Muscle contraction is endergonic and therefore cannot occur without an input of energy. Muscle contraction is coupled to ATP breakdown, making the overall process exergonic. Now muscle contraction can occur. Only 30% of the free energy of glucose is transformed to ATP; the rest is lost as heat.

Function of ATP Cells make use of ATP for: Chemical work – ATP supplies energy to synthesize macromolecules, and therefore the organism Transport work – ATP supplies energy needed to pump substances across the plasma membrane Mechanical work – ATP supplies energy for cellular movements Cellular movements include muscle contraction, movement of cilia and flagella, movement of chromosomes, and so forth.

Metabolic Pathways and Enzymes Cellular reactions are usually part of a metabolic pathway, a series of linked reactions, illustrated as follows: E1 E2 E3 E4 E5 E6 A → B → C → D → E → F → G A-F are reactants or substrates B-G are the products in the various reactions E1-E6 are enzymes. Metabolic pathways may be branched.

An enzyme is a protein molecule that functions as an organic catalyst to speed a chemical reaction. An enzyme brings together particular molecules and causes them to react. The reactants in an enzymatic reaction are called the substrates for that enzyme.

Energy of Activation The energy that must be added to cause molecules to react with one another is called the energy of activation (Ea). The addition of an enzyme does not change the free energy of the reaction, rather an enzyme lowers the energy of activation.

Energy of activation (Ea) Enzymes speed the rate of chemical reactions because they lower the amount of energy required to activate the reactants. On the left is the energy of activation when an enzyme is not present. On the right is the energy of activation when an enzyme is present. Even spontaneous reactions like this one speed up when an enzyme is present.

Enzyme-Substrate Complexes Every reaction in a cell requires a specific enzyme. Enzymes are named for their substrates: Substrate Enzyme Lipid Lipase Urea Urease Maltose Maltase Ribonucleic acid Ribonuclease

A small part of an enzyme, called the active site, complexes with the substrate(s). The active site may undergo a slight change in shape, called induced fit, in order to accommodate the substrate(s). The enzyme and substrate form an enzyme-substrate complex during the reaction. The enzyme is not changed by the reaction, and it is free to act again.

Enzymatic reaction An enzyme has an active site, where substrates and enzyme fit together in such a way that the substrates are oriented to react. Following the reaction, the products are released and the enzyme is free to act again. Some enzymes carry out degradation; the substrate is broken down to smaller products.

Some enzymes carry out synthesis; the substrates are combined to produce a larger product.

Induced fit model These computer-generated images show an enzyme called lysozyme that hydrolyzes its substrate, a polysaccharide that makes up bacterial cell walls. On the left is the configuration of the enzyme when no substrate is bound to it. After the substrate binds (on the right), the configuration of the enzyme changes so that hydrolysis can better proceed.

Factors Affecting Enzymatic Speed Enzymatic reactions proceed with great speed provided there is enough substrate to fill active sites most of the time. Enzyme activity increases as substrate concentration increases because there are more collisions between substrate molecules and the enzyme.

Enzyme Active Site is Saturated Rate of Reaction Substrate Concentration

Temperature and pH As the temperature rises, enzyme activity increases because more collisions occur between enzyme and substrate. If the temperature is too high, enzyme activity levels out and then declines rapidly because the enzyme is denatured. Each enzyme has an optimal pH at which the rate of reaction is highest. A denatured protein is one that has undergone a change in shape and can no longer function normally. A change in pH can alter the ionization of these side chains and disrupt normal interactions, and under extreme conditions of pH, denaturation eventually occurs.

Effect of pH on Enzyme Activity Each enzyme has its own optimum pH. Pepsin Trypsin Rate of Reaction 2 3 4 5 6 7 8 9 pH 24

Effect of Temperature on Enzyme Activity Rate of Reaction 30 40 50 Temperature 23

Effect of Temperature on Enzyme Activity Increasing the temperature causes more collisions between substrate and enzyme molecules. The rate of reaction therefore increases as temperature increases. Effect of Temperature on Enzyme Activity Rate of Reaction 30 40 50 Temperature 23

Effect of Temperature on Enzyme Activity Enzymes denature when the temperature gets too high. The rate of reaction decreases as the enzyme becomes nonfunctional. Rate of Reaction 30 40 50 Temperature 23

Regulation of Enzymes The next several slides illustrate how cells regulate enzymes. For example, it may be necessary to decrease the activity of certain enzymes if the cell no longer needs the product produced by the enzymes.

Regulation of Enzymes genetic regulation of enzymes regulation Cell can turn on DNA genes to build more enzymes when needed genetic regulation regulation of enzymes already produced Cells can use certain chemicals to slow down existing enzymes competitive inhibition noncompetitive Inhibition (next slide) 29

Enzyme Inhibition Enzyme inhibition occurs when an active enzyme is prevented from combining with its substrate. When the product of a metabolic pathway is in abundance, it binds competitively with the enzyme’s active site, a simple form of feedback inhibition. Other metabolic pathways are regulated by the end product binding to an allosteric site on the enzyme.

Competitive Inhibition In competitive inhibition, a similar-shaped molecule competes with the substrate for active sites. 27

Competitive Inhibition This substrate cannot get into active site at this time Active site is being occupied by competitive inhibitor 28

Noncompetitive Inhibition Active site Inhibitor Altered active site Enzyme

Noncompetitive Inhibition The binding of an inhibitor to an allosteric site is usually temporary.   Poisons are inhibitors that bind irreversibly. For example, penicillin inhibits an enzyme needed by bacteria to build the cell wall. Bacteria growing (reproducing) without producing cell walls eventually rupture.

Feedback inhibition This diagram shows the basic metabolic pathway. Enzyme 1 (E1) has two sites: the active site where reactant A binds and an allosteric site where end product F binds.

This diagram shows the active pathway This diagram shows the active pathway. Reactant A binds to the active site of enzyme 1 (E1); therefore, the pathway is active and the end product is produced.

This diagram shows the inhibited pathway This diagram shows the inhibited pathway. When there is sufficient end product F, some binds to the allosteric site of enzyme 1 (E1). Now a change of shape prevents reactant A from binding to the active site of E1, preventing the reaction from occurring, and the end product is no longer produced.

Enzyme Cofactors Presence of enzyme cofactors may be necessary for some enzymes to carry out their functions. Inorganic metal ions, such as copper, zinc, or iron function as cofactors for certain enzymes. Organic molecules, termed coenzymes, must be present for other enzymes to function. Some coenzymes are vitamins. A deficiency in certain vitamins results in the lack of a particular coenzyme and therefore a lack of enzymatic functions. In humans, this eventually results in vitamin-deficiency symptoms.

Enzyme Coenzyme Enzyme