THE ROLE OF ENZYMESENZYMES SPEED UP CHEMICAL REACTIONS.

Everything that happens in a cell Growth Reproduction Interaction with the environment Response to stimuliIs the result of a chemical reaction.A chemical reaction is a change in the arrangementof atoms or molecules that yields different

substances

CHARACTERISTICS OF CHEMICAL REACTIONS

All chemical reactions involve reactants andProducts. Reactants are the atoms, molecules or compounds that enter a into a chemical reaction.Products are the atoms, molecules or compounds that result from the reactionChemical reactions break chemical bonds in one or morereactants and form new bonds in one or more products.

Photosynthesis Reactants Products

(light energy)CarbonDioxide + water Glucose + OxygenCO2 H2O C6H12O6 6O2

The biochemical reactions in living things must occur at certain spped or rate to be useful.

Rate of a chemical reactions depends on: Temperature The concentration of reactants Surface area The presence of a catalystA catalyst is a substance that speeds up the rate

ofa chemical reaction without being changed by

thereaction.An enzyme is a protein that is a biochemicalcatalyst.

Enzymes make chemical reactions within cellpossible or speed them up.Enzymes give reactants a site where they cancome together.The surface of an enzyme has a distinct shape that allows it to interact only with certainsubstrates.Organisms have thousands of enzymesSubstrates bind to a part of the enzyme called theactive site. The shape of the enzyme and substrate

areComplementary.

IEnzymes can form to the shape of its

substrate.They fit together much like a lock and key.

When the reaction finishes, the products are released. The enzyme, which is unchanged , can then repeat the process. It is not used up

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Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College

ACTIVATION ENERGY

For a chemical reaction to occur, reactants must

come together with enough energy to break

existing bonds and form new ones.Enzymes speed up chemical reactions

by reducing the amount of energy that the

substrates need in order to react.The activation energy is the minimum

amount energy needed for colliding molecules to

react.

ENZYME ACTIVITY CAN BE AFFECTED BY: Temperature pH Concentration of enzyme-substrateTemperatureEnzymes for different organisms tend to work best at different temperatures.In humans is about 37°C, in plants 25°C.Enzymes are usually destroyed or denatured attemperatures above 50°C. Denaturing changes theshape. Without the correct shape enzymes

won’t function properly.

pHThe pH of a solution describes how acidic

or basicthe solution is. Most enzymes function

in narrow pH ranges.

1. What best describes how enzymes function in the body? a.  Enzymes are converted into products by the reactions they catalyze. b.  Enzymes lower the activation energy of reactions c.  One enzyme can catalyze many different reactions. d.  An enzyme is used once and then destroyed by the cell

2. The diagram below illustrates a biochemical process that occurs in organisms. The substance labeled catalyst is also known as a(n)

a.  antibodyb.  enzymec.  hormone.d.  inorganic compound

n)

3. The enzyme catalase is involved in the breakdown of hydrogen peroxide into water and oxygen.  During this reaction, the catalase

a.  is unchanged. b.  is used up. c.  is changed into a product. d.  is formed into a new enzyme

4. Catalysts may reduce the amount of activation energy required for a chemical reaction to occur. Platinum (Pt) is a catalyst that is used in catalytic converters in automobiles. In the graphs below, pathway x is a solid line representing the uncatalyzed reaction. The dotted line shows the catalyzed reaction.

Which graph best illustrates the changes in a reaction when the catalyst reduces the amount of energy required?

a. b.

c. d.

5. Even within a single cell, there are a great number of different enzymes. Why are there so many different kinds of enzymes?a. Enzymes are made out of amino acids and fold up into different shapes so they can do different jobs in the cell. If one enzyme quits working, another one can take its place. That way the cell can stay active and keep functioning even if some of the enzymes cannot function.b. Each enzyme is shaped to do one specific task. An enzyme shaped so that it can break down one molecule cannot be used to break down a different molecule. There must be enough different types of enzymes within a cell to do all the tasks the cell requires.

6. Enzymes are used throughout our bodies to build up or break down molecules. Describe how an enzyme breaks down a large molecule into smaller ones.

a. Enzymes are made out of proteins. They have a spot called an active site that can hold a molecule and force the molecule to come apart at the right spot. A protein molecule could fall into the active site of an enzyme and it would break into amino acids. Then a carbohydrate molecule could fall into the active site after the amino acids float away and the enzyme would break it into simple sugars.b. Enzymes are long chains made of amino acids folded into very specific shapes. The active site forms on one side of the enzyme as it folds up. It is shaped like the molecule that the specific enzyme will work on. When the right molecule comes into contact with the active site, the enzyme and molecule bind. This puts strain on the bonds in the molecule, causing the molecule to break at the correct spot.

7. As food travels through the digestive system, it is exposed to a variety of pH levels. The stomach has a pH of 2 due to the presence of hydrochloric acid (HCl), and the small intestine has a pH ranging from 7 to 9. HCl converts pepsinogen into pepsin, an enzyme that digests proteins in the stomach.

Which of the following most likely happens to pepsin as it enters the small intestine?

A. It becomes inactive. B. It begins to replicate. C. Its shape changes to engulf large proteins. D. Its activity increases to digest more proteins.