Lab 4 - Enzymes &The Catalase Lab

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After completing this activity, students will be able to:

• Determine the household use of Hydrogen Peroxide

• Recognize different enzymes and their characteristics

• Compare and contrast the catalase in animal vs. plant cells

• Explain why temperature and pH would have an effect on enzyme activity

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What are Enzymes?

• Enzymes are Biological Catalysts - substances that increase the speed of chemical reactions.

• When an enzyme is present it takes less energy to start a chemical reaction (activation energy)

• Enzymes help maintain homeostasis• Enzymes facilitate metabolism – which is

essential for life

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• Enzymes are proteins.

• Proteins are made up of amino acids

• Enzymes work with a very specific substrate (the molecule acted on by an enzyme) to speed up a reaction

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• Enzymes have one or more deep folds on its surface

• These folds form pockets called active sites • Enzymes act on the substrate, by fitting into

the active site like a puzzle

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Enzymes and their substrates

• Each enzyme has a definite 3-D shape that allows it to bind with its substrate

• Each enzymes acts only on one specific substrate, which means they break down specific substances (like a lock and key)

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Why do we need enzymes?

• Enzymes work to: – Turn leaves colors in the fall (think of the yellows,

oranges, reds, purples)– Ripen foods (this is what makes your bananas

brown, or apples get mushy), – Digest foods after they are eaten, – Produce DNA and hormones

• Without enzymes, life as we know it is not possible

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What affects enzymes in a reaction?

• Temperature• pH

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Temperature

• There is one temperature at which specific enzymes work best.

• This optimal temperature is usually around human body temperature (37.5 oC) for the enzymes in human cells.

• Above this temperature the enzyme structure begins to break down (denature) (ie. fever)

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pH

• Enzymes have an optimal pH. However the optimum is not the same for each enzyme.

• Enzymes are found at different places in your body, and in the environment

• pH would be different in the body vs. stomach

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Factors that affect enzyme activity

• Temperature • Low temperature (cold) = reactions occur slowly• High temperature (hot) = enzymes denature, which can change

the structure of proteins and alter the enzyme’s function forever

• pH• pH scale goes from 0-14• pH of pure water is 7• Basic (pH higher than 7); Acidic (pH lower that 7)• Changes in pH can also change the structure of proteins and alter

the enzyme’s function.• Organisms can only tolerate (stand) small changes in pH because

every cell has a particular pH at which it functions best (homeostasis).

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Examples of Enzymes and their Substrates

Enzyme Substrate Amylase---------------------Starch Maltase----------------------Maltose Sucrase----------------------Sucrose Lipase------------------------Lipids (Fats) Pepsin------------------------ProteinsCatalase--------------Hydrogen Peroxide

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Catalase• 2H202 2H20 + 02 (gas)• The products of the above reaction are oxygen

gas and water, two non-poisonous molecules. In living cells, the oxygen can be used for cellular respiration and the water can be excreted.

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H2O2 is similar to H2O• Hydrogen peroxide is chemically very similar to

water. • Water = H2O,

• Hydrogen peroxide = H2O2. • In chemistry, things can change a lot when you

change the formula.

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• An extra atom of oxygen also makes hydrogen peroxide a very different chemical, which can be dangerous if it is concentrated.

• That is why the H2O2 you get at the grocery is only 3%. The rest is plain water and it is diluted enough to make it safe for household use.

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Scientific Terminology (used in this lab)

• Control – the constant between experimental groups

• Independent variable – the one variable that changes between experimental groups

• Dependent variable – measured variable

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POST LAB

• What causes the bubbles? • Why did some substances bubble more than

others?

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