Phospholipids:
-Bi-layer of amphipathic (both water and non-water properties) phospholipids -The head is hydrophilic (likes water) and the tail is hydrophobic (repels water) |
Cholesterol:
-Only in animal cells -Reduces the movement of phospholipids across the membrane during high temperatures -reduces stiffness of phospholipids during low temperatures Controls fluidity of phospholipids regardless the temperature |
Proteins:
Have different shape, structures, and functions. Placed within the phospholipid bi-layer. The first model that was considered to be the most accurate was the Davson-Danielli model. That included a layer of proteins on top and under the phospholipid bi-layer (the sandwich model). Later, this model was replaced by the Singer-Nicolson model, which states that the proteins lie within the phospholipids and that they are also amphipathic.
Have different shape, structures, and functions. Placed within the phospholipid bi-layer. The first model that was considered to be the most accurate was the Davson-Danielli model. That included a layer of proteins on top and under the phospholipid bi-layer (the sandwich model). Later, this model was replaced by the Singer-Nicolson model, which states that the proteins lie within the phospholipids and that they are also amphipathic.
Evidence of phospholipid Bilayer: In the 1920's, Gorter and Grendel extracted phospholipids of a cell membrane and arranged them in a monolayer, which revelled that it was twice the area of the membrane
Singer-Nicolson model evidence: Singer and Nicolson discovered that the proteins where within the membrane when they freezed the cell and fractured it. When they did this they discovered that the proteins had different shapes and sizes, and that they were also amphipathic.
Singer-Nicolson model evidence: Singer and Nicolson discovered that the proteins where within the membrane when they freezed the cell and fractured it. When they did this they discovered that the proteins had different shapes and sizes, and that they were also amphipathic.
TOK: The explanation of the structure of the plasma membrane has changed over the years as new evidence and ways of analysis have come to light. Under what circumstances is it important to learn about theories that were later discredited?
It is important to understand the theories that were proven wrong so that we can learn from them and where they went wrong because when a similar situation presents itself, we know what is already proven wrong and can't be considered as an option
It is important to understand the theories that were proven wrong so that we can learn from them and where they went wrong because when a similar situation presents itself, we know what is already proven wrong and can't be considered as an option