To determine the percentage of each type of lipid in the plasma membrane by mass, the scientists would follow these general steps:
1. Sample Collection: Obtain samples of the plasma membrane from each type of cell: the cell lining the ileum of a mammal, the red blood cell of a mammal, and the bacterium Escherichia coli.
2. Lipid Extraction: Extract the total lipids from the plasma membrane using appropriate biochemical techniques, such as solvent extraction methods.
3. Separation of Lipid Types: Separate the extracted lipids into different types (cholesterol, glycolipid, phospholipid, and others). This can be achieved using chromatographic techniques like thin-layer chromatography (TLC) or high-performance liquid chromatography (HPLC).
4. Quantification of Each Lipid Type: Measure the mass of each type of lipid. This can be done using various methods like mass spectrometry, colorimetric assays, or NMR spectroscopy.
5. Calculate Total Lipid Mass: Determine the total mass of all the extracted lipids combined.
6. Calculate the Percentage:
- For each type of lipid, such as cholesterol, calculate the percentage by taking the mass of the specific type of lipid, dividing it by the total mass of all lipids, and then multiplying by 100.
The mathematical expression for this calculation is:
[tex]\[
\text{Percentage of specific lipid} = \left( \frac{\text{Mass of specific lipid}}{\text{Total mass of all lipids}} \right) \times 100
\][/tex]
Using this method, the scientists determined the following percentages:
- For the cell lining the ileum of a mammal:
- Cholesterol: 17%
- Glycolipid: 7%
- Phospholipid: 54%
- Others: 22%
- For the red blood cell of a mammal:
- Cholesterol: 23%
- Glycolipid: 3%
- Phospholipid: 60%
- Others: 14%
- For the bacterium Escherichia coli:
- Cholesterol: 0%
- Glycolipid: 0%
- Phospholipid: 70%
- Others: 30%
These percentages represent the relative abundance of each type of lipid in the plasma membrane by mass, reflecting the lipid composition unique to each cell type.
