Macromolecule Lab

The purpose of this investigation was to discover what types of macromolecules are present in a variety of everyday foods. To start, we performed a suite of macromolecule tests on standard solutions (see "Core Concepts" below — used to provide a positive result) and water (to provide a negative result) in order to identify how the results of each macromolecule test would manifest themselves. There are four different macromolecule tests, and each of which identifies whether a single type of macromolecule is present in a solution. The tests are:

1. Benedict's solution, in which equal parts of the eponymous solution and the test subject are mixed and then heated in a boiling water bath for 2 minutes. A change in color indicates a positive test result for monosaccharides.

2. Lugol's iodine, in which 5 parts iodine and 100 parts of the test subject are mixed. A change in color once again indicates a positive result, in this case for polysaccharides.

3. Biuret Reagent, in which 7.5 parts of the reagent are mixed with 20 parts of the test subject. A change in color indicates a positive result for protein.

4. The Paper Bag test, in which a drop of the test solution is allowed to soak into a dry paper bag alongside a drop of water. The translucencies are then compared — the more translucent the subject is, the more fat (lipids) it contains.

After conducting the background research (through which we discovered the above qualities of each test; see the associated document below), we could now start the main experiment. Our group chose to test two very different foods — Broccoli (in raw form) and Cheese Nips (a processed cheese-flavored cracker) — in order to best identify how macromolecules correlate to different aspects of foods. After selecting our foods, we came up with two hypotheses for each:

• When we test broccoli for macromolecules, we will find high levels of carbohydrates and protein.

• When we test Cheese Nips for macromolecules, we will find high levels of fats and carbohydrates.

We went about designing each experiment, largely replicating what had been done in the background research but instead using pastes of each food. After our procedures had been finalized, we conducted each test on each food and collected our data in a table (see below). Finally, we analyzed our data to draw a conclusion — namely, we found our hypotheses to be entirely correct! (This analysis required writing a CLEAR paragraph, a skill from English.)

Test Results and Data

Results and Analysis of the Main Experiment

Results of the Background Research Tests

Core Concepts

Monomer

A monomer is a "simple" molecule. Monomers cannot be reduced into simpler parts, but they can be joined together to form larger structures; that is, they are like building blocks. A so-called monomer of a structure is that structure's "building block", or the molecule that the structure is made up of. We did not directly use this in our tests, but a knowledge of what monomers are helped us understand more about macromolecules.

Polymer

A polymer is a structure formed by many monomers joined together. Polymers are important because they are more complex (by definition), and so they are able to build what would not be possible with monomers alone. Once again, this knowledge was not directly used in the tests, but it helped to give a better picture of our experiments.

Dehydration Synthesis

How does one obtain a polymer? Unlike building blocks, you can't simply squish two monomers together — they just don't fit together in that way. One common workaround to this is what's known as dehydration synthesis, the process of removing the constituents of a water molecule from two monomers (in any combination) in order to make a "gap" where the two can then be fit together. For instance, two amino acids can be joined through dehydration synthesis by removing a hydrogen from one and a hydrogen and an oxygen from the other. As the name suggests, the leftover hydrogen and oxygen form a water molecule, so when these reactions are done water is produced as a byproduct. None of our tests or experiments involved dehydration synthesis, but it was important to learn about nonetheless.

Macromolecule

A macromolecule is one of the four main building blocks of all known life. A macromolecule, as the name suggests, is a polymer built of many monomers, so each macromolecule has its own respective "building block" as well. Every macromolecule has a specific purpose and fills its own role, so together they can build anything. They are:

• Carbohydrates: A family of molecules used for short-term energy storage. They provide "packets" of energy that other structures can use or transfer. The monomer of a carbohydrate is a monosaccharide, or a "simple sugar" (more literally, "single sugar"). Common monosaccharides are glucose (used by the human body for energy) and fructose (found in many sweetened foods). When monosaccharides are joined, they form a polysaccharide, or "complex sugar" (more literally, "many sugar"). Polysaccharides include starch (found in breads), cellulose (used for physical plant structures), or glycogen (also used by the body for energy). As mentioned, the most common source of carbohydrates is through breads and grains.

• Proteins: A family of molecules used to regulate cell processes and perform actions in a living organism. Proteins are the "worker bees" of an organism, as they take on many roles. Some common proteins and sources of protein are muscles, keratin (which makes up hair and nails), enzymes (which break down and digest food for an organism), eggs, and lean meats. The monomer of proteins are amino acids, which form proteins themselves (the polymer).

• Lipids: More commonly known as fats, these organisms provide long term energy storage as well as a few miscellaneous roles (including forming cell walls and sending chemical messages). Lipids are built of a single glycerol molecule connected to three fatty acids, which form a long "tail" behind it. This tail, depending on what fatty acids are used, can be hydrophobic (water-avoiding), which will cause all lipids with that configuration to face away from a water source. These lipids are known as phospholipids, and they are the constituent of many cell walls precisely because of this helpful feature. Fats are most commonly found in oils, but are also present in waxes and vitamins. One final important item about fats is that fatty acids can come in two types — unsaturated fats and saturated fats. Unsaturated fats occur when carbon in the fatty acids bonds twice with its neighbors, thus leaving no room left for extra hydrogen atoms to attach. This type of fat is common in nature. Saturated fats, however, are when the carbon atoms only bond once with their neighbors, thus leaving multiple bonds left to be filled with extra hydrogen. This is less common in nature but occurs very often in processed foods.

• Nucleic Acids: These acids have one job: to store genetic information. Their monomer is the nucleotide, a versatile molecule which can join together with itself into long chains. Joining different types of nucleotides in a row allows information to be encoded, most famously in DNA and RNA.

Obviously, we used this knowledge extensively in our tests, as the entire purpose of the lab was to examine the characteristics of macromolecules.

Standard Solution

A standard solution is a solution for which the qualities are known. For instance, glucose is a standard solution for a monosaccharide test because it is known that glucose contains monosaccharides — thus, you expect a positive result out of a test on it. These solutions are useful to understand how a test result will manifest itself and in order to make sure the test is working — indeed, we used them in this way in our background research tests.

Negative Control Solution

A negative control solution, often water, is a solution which is known to have a negative result in a specific test. Using the example of a monosaccharide test, water is indeed a negative control solution because it contains no monosaccharides — thus the test is expected to return a negative result, so if it does not you know there is an error in the procedure. (Likewise to the standard solution, we used these solutions to verify our understanding of each test in the background research phase.)

Indicator Solution

An indicator solution is the most important part of a test. It is the chemical which will trigger a reaction in the solution being tested, thus making a positive or negative result manifest. The indicator solutions used in our tests were Benedict's solution, Lugol's iodine, and Biuret reagent.

Reflection

This lab was largely a success. To start, my group-mates and I demonstrated good critical thinking skills in our initial hypothesis selection. We thought carefully about our knowledge of macromolecules and applied that knowledge to a selection of unknown foods. In doing so, we had to evaluate which characteristics were most likely present in each food and why that might be the case. Additionally, this project was a success with respect to collaboration. My group and I worked efficiently and effectively together to conduct all the tests in the allotted time period, with each person conducting different parts of the test and helping others when they required it. We were able to manage our time, as good conscientious learners, and ended up having spare time to work on the analysis.

There are always ways to improve, and this project was no exception. Our group's communication was a little lacking, as we were supposed to bring in two foods before the lab but didn't. I brought in the broccoli, thinking that someone else would bring in another food item, but as no one had confirmed what would be brought nobody brought any other food in. So, we had to borrow the Cheese Nips from the classroom supply — not a critical issue in the end, but a potential for improvement nonetheless. Finally, our critical thinking could've been slightly better. On the second day of experiments, a small test tube was broken due to an unexpected rush of water from the faucet. This faucet is known to be extremely unreliable, so had we been slightly more cautious the accident could likely have been avoided. Once again, this was not hugely significant, but it's an important lesson to remember.

Despite these very minor issues, the project was definitely a success. We planned carefully, executed efficiently, and came away with great results.