MediumBiologyHigh School (11–12)Cell Biology › Cell Structure and OrganellesCell Biology › Transport Across the Cell MembraneNumerical
A student bursts red blood cells in water and collects 250 micrograms of their membranes…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student bursts red blood cells in water and collects micrograms of their membranes. (a) About what mass of the sample is protein? (b) What mass is lipid? (c) What mass is left for carbohydrate and other parts? (d) Why is a red blood cell a good source of almost pure cell membrane?
Need a reminder? The key ideaShow
The cell membrane is a lipid bilayer: polar heads outwards, hydrophobic tails inwards, mostly phosphoglycerides, with cholesterol. It also holds proteins (integral, buried; peripheral, on the surface) and carbohydrates. The human red blood cell membrane is about 52 per cent protein and 40 per cent lipid. Fluid mosaic model (Singer and Nicolson, 1972): a quasi-fluid lipid in which proteins move sideways. Passive transport: diffusion and osmosis, no energy. Active transport: against the gradient, using ATP; the Na+/K+ pump moves 3 Na+ out and 2 K+ in for each ATP.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Protein. micrograms.
Step 2. Lipid. micrograms.
Step 3. The rest. micrograms.
Step 4. Why red blood cells. A mature red blood cell has no nucleus and no organelles. So its only membrane is the cell membrane.
Answer: (a) micrograms; (b) micrograms; (c) micrograms; (d) it has no nucleus or organelles, so the membrane collected is almost pure cell membrane.
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