Proteins have four different structural levels. The primary structure is the sequence of amino acids, the secondary structure are coils that result from hydrogen bonds between the backbone of the protein. The tertiary structure is a result of interactions between R groups and the quaternary structure is when two or more polypeptide chains form a macromolecule. Denaturing a protein affects the secondary, tertiary and quaternary structures by breaking the bonds needed to form them. Denaturation is when the native structure of a protein is lost due to a change in pH, salt concentration, temperature or other various environmental factors.
We weighed the milk before we began to denature it. Then we added acid and waited for the milk to denature and coagulate. Once we saw chunks in the milk we weighed a piece of filter paper and folded it into a funnel. From there, we put the milk into the funnel and separated the milk from the denatured protein. We calculated the percentage of protein in the milk after we massed the amount of protein we caught on our filter paper.
| Mass of filter paper alone (g) | .9 g | |
| Mass of paper and dry protein (g) | 1.1 g | |
| Mass of dry protein (g) | .2 g | |
| Mass of empty beaker (g) | 26.7 g | |
| Mass of 15 mL of milk (g) | 10.1 g |
Based on the amount of protein in a 236 mL carton of milk (8 grams), in our 15 mL sample should have yielded .5 grams, which amounts to 5%, after we denatured the milk with the acetic acid. In our milk, we found .2 grams of protein, amounting to 2%. We calculated a -60% error after we denatured the milk. Our high error was most likely due to the fact that we got impatient with our milk and very aggressively stabbed a hole in the filter paper, releasing all of the milk and most of the protein that was still left. After this, we had a lot of milk in our beaker which more than likely had most of that other 3% of protein we should have gotten in the filter paper. In the future, the investigation could be improved by a different means of separating the protein from the milk. Many groups ran into problems when the chunks of protein in the milk got stuck in the hole at the bottom of the filter paper. Instead, those groups used a coffee filter to squeeze the milk out and from what we saw, that yielded more protein. We were expecting to find less than 5% protein because we thought that the acid would eat away at the protein in the milk. We found less than 5% but for more obvious reasons than the acid eating the proteins.
In a 15 mL sample of milk there should have been .5 grams of protein. Our data does not support this claim, due to the fact that we lost some protein after we poked a large hole in the filter paper.
Fitzpatrick, Kathleen, and Erin Barley. "The Structure and Function of Large Biological Molecules." 23 Sept. 2014. Web.
