EasyBiologyHigh School (11–12)Cell Biology › Cell Structure and OrganellesCell Biology › Transport Across the Cell MembraneConceptual
A scientist joins a glowing dye to the proteins on one small patch of a cell's surface…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A scientist joins a glowing dye to the proteins on one small patch of a cell's surface. Within a few minutes, the glow has spread evenly over the whole cell. (a) Which model of the membrane does this support? Who proposed it? (b) What property of the lipid layer lets the proteins spread? (c) Name two jobs of the cell that need this property.
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. The model. The proteins moved sideways, so they are not fixed. This supports the fluid mosaic model of Singer and Nicolson.
Step 2. The property. The lipid layer is quasi-fluid, so proteins can make lateral movements in it.
Step 3. Its uses. Fluidity is needed for cell growth, junctions between cells, secretion, endocytosis and cell division.
Answer: (a) the fluid mosaic model, Singer and Nicolson; (b) the quasi-fluid nature of the lipid layer; (c) any two of cell growth, forming junctions, secretion, endocytosis and cell division.
Discussion (0)
Log in to join the discussion.
Loading…