Question

Proteins are important food nutrients. A technician working at a food company is interested in the nutritional content of seeds/nuts. She runs a PAGE with samples from two different seed extracts. She runs multiple lanes of the staples. The gel is stained with Coomassie Blue. Seed extract No. 1 has three faint bands at 25, 30, and 35 kDa. Extract No. 2 has two bands at 25 and 35 kDa, and the bands are very dark. What might she conclude from her results about the nutritional value of the seed extracts

Answer 1

Answer: Sample 1 then, has more variety of proteins but less quantity of each one, while sample 2 has less variety but more quantity of the two proteins present.

Explanation:

Proteins are molecules found in the cells of all living organisms. A protein is composed of monomers called amino acids linked together by peptide bonds. To analyze proteins, a technique called SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis) is used. This technique is used to separate proteins according to their electrophoretic mobility, depending on polypeptide chain length, molecular mass, post-translational modifications and other factors. SDS (sodium dodecylsulfate) is an anionic surfactant compound that breaks non-covalent bonds in proteins, denatures them causing these protein molecules to lose their native conformation and provides the polypeptide with a negative charge that is proportional to the chain length (the number of amino acids) and, therefore, to the molecular mass of the protein. The electrostatic repulsion created by the binding of SDS to the protein is one of the causes of the protein losing its native conformation, thus eliminating the differences in conformation of the different proteins to be separated in the gel.

An electric current is applied to the gel where the proteins are seeded, causing the negatively charged proteins to migrate through the gel in the direction of the anode (positively charged region). Short proteins will move more easily and faster through the pores of the gel, while larger proteins will find it more difficult to do so. After a certain time, the proteins will have migrated according to their size (measured in kDa or kiloDaltons). After electrophoresis, the gel should be stained with Coomassie blue or silver stain, allowing visualization of the separated proteins. After staining, the different proteins will appear as distinct bands on the gel. In addition, the higher the amount of a protein, the more intense the color of its band will be.

Extract No. 1 shows three bands: 25, 30 and 35 kDa. This means that it has three different proteins, each with a different molecular weight. Extract number 2 shows two bands: 25 and 35 kDa. It means that this sample has only 2 proteins. And being bands of higher intensity, we can say that there is more of each protein.

Sample 1 then, has more variety of proteins but less quantity of each one, while sample 2 has less variety but more quantity of the two proteins present.