9 Lab Protocol: Biologically Important Molecules

Week 1 – Students will perform experiments on milk and trypsin. They will be able to ask questions about which biomolecules are present in milk and which are present in the trypsin solution on week 1. The aim is to give them a solid understanding of how to work with reagents such as:

Biuret (protein)

Benedict’s (reducing sugars)

Iodine (starch)

Sudan IV or ethanol emulsion

Questions about the content of milk can be formed by students through discussion of their previous knowledge of milk as a food. Discussion about what changes would occur to the biomolecules in milk through digestion by various enzymes as well as the production process of milk. For example, the iodine test is commonly used to test for presence of starch as starch is a common adulteration product used to increase volume or thickness https://safemilklabs.com/detecting-starch-in-milk-the-iodine-test/.

More discussion around the various types of milk found in grocery stores and how different types of milk would react with one of the reagents.

Types of milk that can be used – 0% Skim Milk, Lactose-free Milk, 2%+ Milk (+ Protein), 5% Light Cream, 10% Table Cream, 35% Whipping Cream, Almond Milk, Cashew Milk, Coconut Milk , Oat Milk, Soy Milk

Each group will work on one table to test content of various samples. They will assess products of using each reagent in their milk to test for present of sugars, proteins, and starch. It is important not to tell students what their samples are or what they should see in the results. It is also important for students to use the same 3-4 samples in week 1 and in week 2. This places focus on the question of “what’s in the sample?” as opposed to “what does a positive result look like?”.

They will make observations based on color changes in biuret – how much protein is in each sample (on a qualitative scale like 1 though 5).

Week 2 – Students will use the same samples in week 1 and now test the effect of using an enzyme that digests protein or sugars. They are still gathering data about the protein, sugar, starch, fat content of their samples.

It is important for students to get together and discuss their results from the previous week. They will form hypothesis and ask questions about the content of their milk samples. They may also make predictions about which test they would use to check for breakdown of either protein or sugars. Here is where th

Then, they will use an enzyme that they know breaks down protein – but not much else details. Here they will test various physical factors on the effect of the enzyme on their sample. Trypsin has a visible effect on milk protein – casein precipitates.

Factors they can look at – pH, temperature, enzyme concentration. I like the use of serial dilutions of trypsin and they can gather data on relationship between concentration and rate of reaction.

By the end of this two week experiment, students will have hypothesized about what contents are in their milk products. They will have gathered qualitative evidence using various reagents to check for various biomolecules. They will then have gathered more evidence on the content of their samples using enzymes to digest their predicted substrate and also how temperature and pH effects the action of that enzyme.