Lab 4 - Enzymes &The Catalase Lab

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 make it so life is possible

• Enzymes are proteins.• Proteins are made up of amino acids• Enzymes work with a very specific substrate to

speed up a reaction

Enzymes are large proteins with one or more deeps folds on its surface, these

folds form pockets (active sites). Enzymes act on the substrate, by

fitting into the active site like a puzzle

Enzymes and their substrates• Each enzyme has a definite

3-D shape that allows it to bind with its substrate

• Substrate- substance on which an enzyme acts during a chemical reaction

• Enzymes act only on specific substrates, which means they break down specific substances (like a Lock and Key)

Why do we need enzymes?

• All activity of life depends on them. • The leaves turning green in the spring, the

ripening of foods, the digestion of food, the production of DNA and hormones -- all require enzymes.

• Without enzymes life as we know it is NOT possible!

What affects enzymes in a reaction?

• Temperature• pH

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) (fever)

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

• Enzymes in the body vs. stomach

Factors that affect enzyme activity

• Temperature • Low temperature (cold)=reactions are too slow• High temperature (hot)=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.

Examples of Enzymes and their Substrates

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

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.

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

water. Where the chemical formula for water is H2O, hydrogen peroxide is H2O2. A molecule of water contains two atoms of hydrogen and one atom of oxygen. The only difference between hydrogen peroxide and water is a little oxygen. That may not sound like much of a difference, but it is. In chemistry, things can change a lot when you change the formula.

Diluted• 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 stuff 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.

Scientific Terminology

• Control – the CONSTANT between experimental groups

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

• Dependent variable – MEASURED RESULT

• Follow instructions on diagram on page 4-8!• Information for tubes 5 and 6 is switched on

page 4-9.• Information on back table is correct.

• Grab tube rack, follow set-up directions on whiteboard

• **make sure tissue cubes are small enough to remove after experiment!!!**

• Go back to your table, follow lab notebook protocol for each experiment

POST LAB

• OK, then what causes the bubbles? • Why did some substances bubble more than

others?