Let's learn a little biology

What exactly is an enzyme?

An enzyme is a biological catalyst. Biological means coming from a living organism - a body, a plant, a cell, and so on. Wait, what's a catalyst? A catalyst is anything that makes a chemical reaction go faster. So, an enzyme is a protein that is secreted by a cell that makes a biochemical reaction go faster.

Enzymes are part and parcel of our digestive system. The first enzymes your food encounters are in saliva. The salivary enzyme amylase helps break down starches to more simple sugars. In the stomach, pepsin catalyzes the breakdown of proteins and gastric lipase catalyzes the breakdown of butter fat. The next organ involved in secreting digestive enzymes is the pancreas. It secretes tripsin, the enzyme that catalyzes breaking proteins into amino acids, pancreatic amylase, which helps turn carbohydrates into simple sugars, and many others. Finally, our small intestines secrete enzymes such as lactase, which breaks down milk sugars, and sucrase, which helps table sugar turn into glucose and fructose.

You may have noticed a pattern. Many enzymes end in "-ase". Not all enzymes have that handy clue built in, e.g., tripsin. Chances are, if you see a word ending in "-ase", it is probably some kind of enzyme.

How do enzymes work? Enzymes are specific, which means they only act on one thing. Sucrase, for instance, only catalyzes the breakdown of sucrose into its two simple parts, fructose and glucose. Another example is gastric lipase which only works on butter fat. Scientists think enzymes work like a lock and key. The substrate, the specific target, has a shape that fits perfectly into the enzyme.[5366]

Yay! We get to smear raw meat on the counter.

Testing for catalase

Catalse is found in all animal cells. It helps convert hydrogen peroxide (H2O2) to plain water (H2O) and oxygen gas (O2). Here's an engaging, albeit a little disgusting, way of teaching your students about catalase.

What you need:

  • 1/4 lb. of raw ground meat (beef works best, but turkey or chicken will do)
  • a clean counter
  • a bottle of hydrogen peroxide
  • a few cotton swabs (Q-tips or other brand)
  • paper towels
  • disposable gloves (so the students don't get meat all over themselves)
Day 223 - Raw meat is so raw

Photo Credit: tsheko on Flickr

What the students do:

  1. Put on a pair of disposable gloves. Take a small amount of ground meat and rub it all around the countertop in front of you.
  2. Clean off the meat as best you can with a few paper towels.
  3. Dip a Q-tip into the hydrogen peroxide.
  4. Swab the countertop with the Q-tip.
  5. If there are bubbles, there is catalase. And if there is catalase, there is still some meat left on the counter.

This is also a great lesson for teaching about cleaning raw meat products and avoiding cross-contamination when cooking.

What you do:

  1. Divide your students into three groups. Or have one student do the experiment three times.
  2. One groups cleans with paper towels.
  3. The second cleans with a disinfectant wipe (such as Lysol).
  4. The third group cleans the counter with hot soapy water.
  5. Compare to see which group has the most (or least) catalase activity, and, therefore, the cleanest counttertop.

Unjelled gelatin

Proteases in pineapple and papaya

Several fruits contain proteases.[5368] What do you think proteases are? They are enzymes (ends in "ase") that catalyze the breakdown of proteins. Papaya, pineapple, kiwi, and melons contain proteases. The protease in papaya is called papain[5367] and is often used as a meat tenderizer, and the one in pineapple is called bromelain. Because of its protein-digestive action, pineapple has been used as a natural remedy for indigestion and inflammation by the people of Central and South America for centuries.[5369]

Gelatin is a web of proteins that contains water and sugar.[5368] If you add a protease to gelatin, it won't form into a web. Here's a great way to demonstrate this.

lime jello with pineapple chunks

What you need:

  • 2 boxes of unmade gelatin
  • fresh pineapple, cubed
  • canned pineapple chunks
  • 2 pans

What you do:

  1. Make a box of jello according to the package directions. Pour the unjelled gelatin into a pan. Add some fresh pineapple chunks.
  2. Make the second box of jello, pour into the second pan, and add some canned pineapple chunks.
  3. Put both pans into the refrigerator to set. This takes about 4 hours.
  4. Remove both pans and compare. The gelatin with the fresh pineapple will still be soupy, because the proteases help break down the protein structure of the gelatin. The canned pineapple was heated as part of the canning process; this inactivated the proteases in the pineapple.

Photo credit: jeffrey loo on Flickr