A student completed a lab investigation on an unknown biomolecule sample. The student ran a test and discovered that the sample contains only carbon. hydrogen, and oxygen. The student then rubbed a small amount of the sample on a piece of paper and noticed that the sample left a greasy stain. Which of the following biomolecules does the student have?
A Nucleic acids
B Carbohydrates
C Lipids
D Proteins
The correct answer and explanation is:
The correct answer is C) Lipids.
Lipids are a group of biomolecules that primarily consist of carbon, hydrogen, and oxygen, which matches the elements found in the sample. Lipids are characterized by their hydrophobic (water-repelling) nature, and they do not dissolve in water. The greasy stain left on the paper is a key indicator of lipids. Lipids, such as fats and oils, tend to leave a stain on paper because they are nonpolar substances that can interact with the paper’s surface and leave behind a mark.
Nucleic acids, carbohydrates, and proteins do not generally leave greasy stains on paper. Nucleic acids (such as DNA and RNA) are primarily composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus. They are not greasy and have distinct functions related to genetic information storage and protein synthesis. Carbohydrates (such as sugars and starches) also consist of carbon, hydrogen, and oxygen, but they are hydrophilic (water-loving) and do not leave a greasy residue. Proteins, which are made of amino acids, can have elements like nitrogen and sulfur, but they do not leave a greasy mark on paper either.
The greasy stain is a hallmark feature of lipids, which includes substances like fats, oils, and waxes. These molecules are used for energy storage, insulation, and making up cellular membranes, particularly phospholipids. Lipids are important for maintaining cell structure and function and are an essential part of the diet for their energy-providing capabilities.
In conclusion, the sample is most likely a lipid, as indicated by the presence of carbon, hydrogen, and oxygen, along with the greasy stain left on paper.