The Chemistry of Life

Chemical Basis of Life

Enzymes

Lesson Objectives

• Describe what happens in a chemical reaction, and identify types of chemical reactions.

• Explain the role of energy in chemical reactions, and define activation energy.

• State factors that affect the rate of chemical reactions.

• Explain the importance of enzymes in organisms, and describe how enzymes work.

Introduction

• Chemical compound usually very different from substances that make it…– Example: Sodium chloride

NaCl (table salt)

WHAT ARE CHEMICAL REACTIONS?

• Chemical reaction: a process that changes some chemical substances into other chemical substances– substances that start a chemical reaction are called

reactants• reactants are used up to create the products

– substances that form as a result of a chemical reaction are called products

• Example: Methane needs oxygen to burn.

CH4 + 2O2 CO2 + 2H2O + heat + light

Methane Oxygen Carbon Water FIRE dioxide

Chemical Equations

• Can be represented by a chemical equation (see below)

• Arrow in a chemical equation separates the reactants from the products and shows the direction in which the reaction occurs

CH4 + 2O2 CO2 + 2H2O + heat + light

Methane Oxygen Carbon Water FIRE dioxide

Types of Chemical Reactions• combustion reaction occurs when a compound or element

burns in oxygen, like methane burning in presents of oxygen• Substance burns in presence of oxygen• synthesis reaction occurs when two or more chemical

elements or compounds unite to form a more complex product. For example, nitrogen and hydrogen unite to form ammonia:

• decomposition reaction occurs when a compound is broken down into smaller compounds or elements. For example, water breaks down into hydrogen and oxygen:

• substitution reaction occurs when one element replaces another element in a compound. For example, sodium replaces hydrogen in hydrochloric acid, producing sodium chloride and hydrogen gas:

N2 + 3H2 ---> 2NH3

2H2O ---> 2H2 + O2

2Na+ + 2HCl ---> 2NaCl + H2

CHEMICAL REACTIONS AND ENERGY

Some chemical reactions consume energy, whereas other chemical reactions release energy.

Exothermic Reactions• RELEASE ENERGY

– example is the combustion of methane described at the beginning of this lesson

• In organisms, exothermic reactions are called catabolic reactions. – catabolic reactions break down molecules into smaller

units. – an example is the breakdown of glucose molecules

for energy. • Exothermic reactions can be represented by the

general chemical equation:

Reactants → Products + Heat.

Energetics of Ionic Bond Formation: NaCl formation

• The formation of ionic compounds (like the addition of sodium metal and chlorine gas to form NaCl) are usually extremely exothermic.

• The loss of an electron from an element:• Always endothermic (takes energy to strip the e' from the atom)• Na(g) -> Na+(g) + 1e- DH = 496 kJ/mol• The gain of an electron by a nonmetal:• Generally exothermic (energy released)• Cl(g) + 1e- -> Cl-(g) DH = -349 kJ/mol• The formation of NaCl from Na and Cl would thus require the input

of 147 kJ/mol. However, it appears to be a highly exothermic reaction.

• Energy is released

Endothermic Reactions

• CONSUME ENERGY– example is the synthesis of ammonia, described earlier.

• In organisms, endothermic reactions are called anabolic reactions. – anabolic reactions construct molecules from smaller units. – an example is the synthesis of proteins from amino acids.

• Endothermic reactions can be represented by the general chemical equation:

Reactants + Heat → Products.

N2 + 3H2 ---> 2NH3

Activation Energy

• Whether reactions are exothermic or endo-thermic, they all need energy to get started. This energy is called activation energy.

Short Video & Demo

• Let’s explore activation energy.

http://www.youtube.com/watch?v=VbIaK6PLrRM&feature=related

Rates of ChemicalReactions

• Chemical reactions in organisms are involved in processes ranging from the contraction of muscles to the digestion of food.

– For example, when you wave goodbye, it requires repeated contractions of muscles in your arm over a period of a couple of seconds. A huge number of reactions must take place in that time, so each reaction cannot take longer than a few milliseconds. If the reactions took much longer, you might not finish waving until sometime next year.

• Factors that help reactant molecules collide and react speed up chemical reactions. These factors include the concentration of reactants and the temperature at which the reactions occur.

– Reactions are usually faster at higher concentrations of reactants. The more reactant molecules there are in a given space, the more likely they are to collide and react.

– Reactions are usually faster at higher temperatures. Reactant molecules at higher temperatures have more energy to move, collide, and react.

ENZYMES AND BIOCHEMICAL REACTIONS

• Rate of most biochemical reactions must be increased by a catalyst (a chemical that speeds up chemical reactions). – In organisms, catalysts are called enzymes– enzymes are not reactants

• Special properties of enzymes:– Speed up ONLY reactions that normally occur slowly– They help the reactants interact but are not used up in the reactions. – May be used over and over again. – Are usually highly specific for particular chemical reactions. They

generally catalyze only one or a few types of reactions. – Can catalyze up to several million reactions per second.

• As a result, the difference in rates of biochemical reactions with and without enzymes may be enormous. A typical biochemical reaction might take hours or even days to occur under normal cellular conditions without an enzyme but less than a second with the enzyme.

Metabolism

• Sum of all chemical reactions (anabolic and catabolic) in an organism…

• Set of chemical reactions that sustain life; allow organisms to grow and reproduce, maintain their structures, and respond to their environments.

Enzymes: Characteristics• Activation energy – enzymes reduce the amount of

activation energy needed to start a reaction. For chemical reactions to take place, the reactants must collide with enough energy so that existing bonds will be broken and new bonds will be formed.

• Rate of reaction – sped up with an enzyme present because less activation energy is needed; without them some reactions would take days to happen not a split second as they do with enzymes.

Characteristics continued…• Works on – substrate (reactants of enzyme-catalyzed

reactions)• Connects at – active site on the enzyme (which is

complementary to a site on the substrate)• Sometimes named – catalysts; enzyme-substrate

complex; lock-n-key model• Are made of – proteins by cells that act as biological

catalysts• Are NOT – consumed by the reaction and can work

over and over again

How Enzymes Work

Lock-and-Key Model

• Enzyme reacts only with a substrate

• Term used to describe enzyme-assisted reaction lock-and-key model– Substrate: a specific molecule that the

enzyme chemically recognizes

• Enzymes bind to the substrates at something called the active site

Animation of how enzymes work

• http://www.youtube.com/watch?v=CZD5xsOKres&feature=related

• NOW, Look at the diagram on page 3 of packet and explain how enzymes and substrates work together

Enzymatic Activity Criteria• Activities of enzymes depend on the temperature, ionic

conditions, and the pH of the surroundings. – Some work best at acidic pHs, while others work best in neutral

environments.– Digestive enzymes secreted in the acidic environment (low pH) of the

stomach help break down proteins into smaller molecules. • The main digestive enzyme in the stomach is pepsin (breaks proteins into

smaller chains of amino acids), which works best at a pH of about 1.5. • Trypsin is another enzyme in the small intestine (breaks amino acid chains

into amino acids), which is not an acidic environment. Trypsin’s optimum pH is about 8.

• Biochemical reactions are optimal at physiological temperatures. – For example, most biochemical reactions work best at the normal body

temperature of 98.6˚F (37 ˚C). Many enzymes lose function at lower and higher temperatures.

– At higher temperatures, an enzyme’s shape deteriorates and only when the temperature comes back to normal does the enzyme regain its shape and normal activity.

Importance of Enzymes

• Enzymes are involved in most of the chemical reactions that take place in organisms.

• Needed for reactions that regulate cells, enzymes allow movement, transport materials around the body, and move substances in and out of cells.

• In animals, another important function of enzymes is to help digest food. – Digestive enzymes speed up reactions that break down large

molecules of carbohydrates, proteins, and fats into smaller molecules the body can use.

– Without digestive enzymes, animals would not be able to break down food molecules quickly enough to provide the energy and nutrients they need to survive.

Lesson Summary• A chemical reaction is a process that changes some chemical

substances into others. It involves breaking and forming chemical bonds. Types of chemical reactions include synthesis reactions and decomposition reactions.

• Some chemical reactions are exothermic, which means they release energy. Other chemical reactions are endothermic, which means they consume energy. All chemical reactions require activation energy, which is the energy needed to get a reaction started.

• Rates of chemical reactions depend on factors such as the concentration of reactants, pH, and the temperature at which reactions occur. Both factors affect the ability of reactant molecules to react.

• Enzymes are needed to speed up chemical reactions in organisms. They work by lowering the activation energy of reactions.

POP QUIZWrite the word(s) that are the correct answer only.1. Enzymes are (carbohydrates///proteins).2. Enzymes (speed up///slow down) the chemical

reactions in your body.3. Enzymes are (used up///not used up) during

their reactions.4. The specific molecules that enzymes react

with are called (substrates///reactants).5. The lock-and-key model is used to describe

(chemical bonding///enzyme-substrate complex).

Was energy released or absorbed during this reaction?

POP QUIZANSWERS>>>>

1. Enzymes are (proteins).2. Enzymes (speed up) the chemical

reactions in your body.3. Enzymes are (not used up) during their

reactions.4. The specific molecules that enzymes

react with are called (substrates).5. The lock-and-key model is used to

describe (enzyme-substrate complex).

Was energy released or absorbed during this reaction?

•Released….product below reactants