Describe the modern fluid mosaic model of membrane structure.

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The fluid mosaic model was proposed in 1972 by Singer and Nicolson. Their original model has changed over time; however, it is still the best model for explaining the cell membrane's structure and function. The core of the fluid mosaic model states that the cell membrane is primarily composed of...

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The fluid mosaic model was proposed in 1972 by Singer and Nicolson. Their original model has changed over time; however, it is still the best model for explaining the cell membrane's structure and function. The core of the fluid mosaic model states that the cell membrane is primarily composed of three things. Those are phospholipids, cholesterol, and proteins. The phospholipids make up the majority of the cell membrane, and they are composed of a head and two tails. The head is hydrophilic which means it is attracted to water. The tails are water repellent or hydrophobic. Because of this affinity or aversion to water, the phospholipids arrange themselves tail to tail so that the head portion faces the watery environment that is either inside the cell or outside the cell. If you looked at it on edge, the tail to tail phospholipids would appear as a double layer. This is why the cell membrane is said to be a phospholipid bi-layer. The proteins and cholesterol are distributed into the bi-layer, and the proteins are divided into "integral" and "peripheral" proteins. Integral proteins stick out of the phospholipid layer on both sides, but the peripheral proteins do not extend all the way through.

Because the cell membrane is composed of different molecules distributed throughout the membrane, it forms a pattern called a "mosaic." The fluid part is because the molecules are constantly moving in a "fluid" way. The cholesterol is integral to this fluidity. It prevents lower temperatures from limiting fluidity, and it prevents higher temperatures from creating too much fluidity. This is why the cholesterol is sometimes referred to as a "buffer."

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