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Davson-Danielli Model & Singer-Nicolson Fluid Mosaic Model

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Uploaded on Oct 14, 2008

Davson-Danielli Model & Singer-Nicoloson Fluid Mosaic Model

Video Summary Life occurs in an aqueous environment. Proteins are essential to life because they help maintain solute homeostasis. The phospholipid bi-layer, which is found in cell membranes, is one way a phospholipid arranges itself. The phosphate head, which is hydrophilic, moves toward the water. The hydrocarbon tail is hydrophobic. The Davson-Danielli model is an idea proposed on how cells regulate their environment. The proteins are on the outside of the bi-layer membrane. However, membranes need to allow for solute particles to pass back and forth. When proteins are on the outside, it blocks the solutes from passing through, preventing homeostasis. Therefore, we have to reject this model. In the Singer-Nicholson Fluid Mosaic Model, the integral proteins are embedded in the bi-layer. They have the ability to open up and let particles move back and forth. This model differs from the Davson-Danielli Model because it recognizes that biological systems are open systems that interact with their environments. This is a much more dynamic entity. This model allows for homeostasis, or a balance. The embedded proteins act as gatekeepers. They transport with the concentration gradient. Passive transport and facilitated transport move from a region of high solute concentration to a region of low solute concentration. Neither of these processes require energy because they are working with the concentration gradient. The active transport uses proteins to move substances from a region of low to high and uses energy to accomplish this.

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