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The Liver: Helping Enzymes Help You!

A fun chemistry challenge from Science Buddies
liver enzymes



George Retseck

Key concepts
Chemistry
Acids
Bases
Temperature
Physiology
Molecular biology

Introduction
Your liver is important for cleaning up any potentially dangerous substances you consume. But how does it do it?—With a little help from some complex chemistry. Within your liver, as within every tissue in the body, many chemical reactions occur. Often these reactions require "help" to happen at a faster speed, and this can be supplied by enzymes—tiny types of proteins.

The liver uses specialized enzymes to help it break down toxic substances and make them safer for the body to process. But an enzyme, just like the chemical reactions it modifies, needs certain conditions to do its work. So, some environments can make a liver enzyme effective, whereas others can prevent it from working at all.

Background
A chemical reaction occurs when compounds come together and their molecules interact to form new compounds. Sometimes these reactions happen by themselves, are usually very fast and spontaneous, and give off energy. Other chemical reactions need energy, without which they would proceed very slowly or not at all. Enzymes can help speed up these types of chemical reactions.

Enzymes are large proteins that speed up the rate of a chemical reaction by acting as a catalyst. A catalyst provides the necessary environment for the reaction to occur, thereby quickening it. Certain catalysts work for certain kinds of reactions; in other words, each enzyme has a particular type of reaction that it can activate. Enzymes can be very fussy and sometimes need to be in certain environments or conditions to work well—or at all. Some enzymes can even be damaged, such as when exposed to too much heat. A damaged enzyme may no longer work to catalyze a chemical reaction.

Catalase is an enzyme in the liver that breaks down harmful hydrogen peroxide into oxygen and water. When this reaction occurs, oxygen gas bubbles escape and create foam.

Materials
•    Raw liver (fresh or frozen, thawed; one quarter pound)
•    Knife
•    Cutting board
•    Blender
•    Water
•    Refrigerator
•    Medicine dropper
•    Large plate
•    Hydrogen peroxide (new or recently purchased bottle works best)
•    Measuring teaspoon
•    Two bowls
•    Vinegar
•    Baking soda
•    Microwave-safe bowl (with a cover)
•    Microwave oven

Preparation
•    Completely disinfect any surface that the raw liver touches during this activity.
•    On the cutting board, carefully cut the liver into little, cube-shaped pieces, about one to two centimeters long. Be careful using the sharp knife. (An adult may need to help with this.)
•    Place the liver cubes into a blender and add an equal volume of water. Blend on high speed, pulsing when necessary, until the liver is smooth and no chunks are present. Be careful of the sharp blades in the blender.
•    Keep the blended liver in the refrigerator.

Procedure
•    Put one drop of the blended liver on the large plate. To the blended liver drop, add one drop of hydrogen peroxide. You should see a lot of bubbles! What do you think the bubbles are made of? This shows that the liver enzyme catalase is working to start the chemical reaction that breaks down the hydrogen peroxide that would be harmful to the body into less dangerous compounds.
•    To test the effect of an acid on the liver enzyme, put one teaspoon of the blended liver in a bowl and mix it well with one teaspoon vinegar. What is the color and consistency of this mixture? Put one drop of the mixture on a clean part of the large plate and add one drop of hydrogen peroxide to it. Compared with the untreated blended liver, did more, less or about the same amount of bubbles form? Did they form more slowly, more quickly or at about the same rate?
•    To test the effect of a base, put one teaspoon of the blended liver in a bowl and mix it with one teaspoon baking soda. What is the color and consistency of this mixture? Put one drop of the mixture on a clean part of the large plate and add one drop of hydrogen peroxide to it. Did more, less or about the same amount of bubbles form? Did they form more slowly, more quickly or at about the same rate?
•    To test the effect of heat, put one teaspoon of the blended liver into a microwave-safe bowl. Cover the bowl and microwave it on high for 20 seconds. How does the blended liver look after heating? Remove a drop-size amount of the heated liver and put it on a clean part of the large plate. Add one drop of hydrogen peroxide to it. Did more, less or about the same amount of bubbles form? Did they form more slowly, more quickly or at about the same rate?
•    Based on your observations, under which condition(s) does it look like the enzyme works best? Which condition(s) makes it work the worst? Why do you think this is so?
•    Extra: Try experimenting with other conditions. For example, try freezing some blended liver or mixing it with salt and then test the enzyme's activity. Or you could try adding more than one teaspoon of vinegar or baking soda and then test the enzyme. Under which conditions does the enzyme work well, and under which ones does it work poorly?
•    Extra: You could try this activity again using another enzyme, called bromelain, which digests proteins and can be extracted from pineapples. One protein that is fun to digest using bromelain is gelatin, which is found in many puddings and gelatinous desserts. How do different conditions affect the ability of bromelain to digest proteins?

Observations and results

When exposed to hydrogen peroxide, did the blended liver bubble less when mixed with either the vinegar or baking soda compared with when it was untreated? Did it bubble even less after it was microwaved?

An enzyme needs certain conditions to work, and the ideal environment can be a hint as to where the enzyme normally works in the body. And because different body tissues have distinct environments—acidic or warm—each enzyme is tuned to work best under specific conditions.

Different tissues in the body have different pHs (pH is a measure of how basic or acidic a solution is). The liver maintains a neutral pH (about pH 7), which is easiest for its enzymes, such as catalase, to work in. Consequently, when exposed to hydrogen peroxide the liver should have produced more bubbles (oxygen gas), and at a faster rate, when it was untreated than when exposed to vinegar or baking soda. (It may have bubbled more when treated with baking soda, compared with vinegar, because it might have been better able to return the pH to around 7.)

Similarly, enzymes in the liver are also used to functioning at body temperature (37 degrees Celsius), so microwaving the blended liver to a temperature hotter than that should have damaged the catalase enzyme and clearly decreased the amount of bubbles when it was exposed to hydrogen peroxide.

Cleanup
Safely dispose of any raw liver meat used in this activity by putting it in the trash when you are done. Completely disinfect any surfaces that the raw liver meat touched during this activity, and be sure to thoroughly wash your hands with soap and warm water.

More to explore
"Enzymes Make the World Go 'Round" from Rader's Chem4Kids.com
"Your Liver" from KidsHealth
"Catalase" from David Goodsell and RCSB Protein Data Bank
"Liver Stinks!" from Science Buddies
"Which Fruits Can Ruin Your Dessert?" from Science Buddies


This activity brought to you in partnership with Science Buddies
ScienceBuddies

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