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How Does Cholesterol Affect Membrane Fluidity
Cholesterol is an organic substance that belongs to the steroid family. This waxy substance is extremely important in order for the body to carry out several functions such as producing steroid hormones, vitamin D, and other compounds from which the body synthesizes bile acids.
Due to the above-mentioned reasons, the body has the capacity to produce cholesterol – this process occurs in the liver to be more precise – however, this is not the only source of cholesterol as it can also be found in animal foods like egg yolks, milk, cheese, and meat.
Moreover, cholesterol is the primary substance which composes the membrane that surrounds each cell and it has the capacity to either make the cell membrane fluid or rigid, due to its chemical characteristics.
Interested to understand how this process works? Follow me in this article for a quick review of the cell membrane, some factors that can affect membrane fluidity, and to understand how cholesterol affects membrane fluidity.
The cell membrane, also known as the plasma membrane is a semipermeable lipid bilayer, whose function is to separate the interior of the cell from its outside surroundings. This thin membrane surrounds every living cell.
Inside the cell membrane are the cell’s components such as lipids, carbohydrates, proteins, and many other substances implicated in cellular metabolism, whereas in the outside of the cell membrane there is a water-based environment filled with acids, ions, alkalis, and nutrients that the cell absorbs in order to live and grow.
Some of the functions of the cell membrane are acting as a barrier to maintain undesired substances outside the cells; providing structural support for the cell; transporting nutrients into the cell, and also transporting toxic substances outside of the cell.
Cell Membrane Components
In terms of composition, cell membranes are composed primarily of fatty-acid lipids, but it also contains proteins and carbohydrates. In 1972 scientists proposed that the cell membrane resembles a “fluid mosaic” due to the fact that the phospholipids, cholesterol, and proteins move fluidly and freely, continually sliding past one another.
Lipids are the predominant component of the membrane cell and there are three types of them, phospholipids, glycolipids, and sterols (mainly cholesterol). Their distinguishing characteristic is that they have the capacity to dissolve in organic solvents and part of them is attracted and soluble in water.
How Does Cholesterol Affect Membrane Fluidity – Importance of Membrane Fluidity
Maintaining membrane fluidity is extremely vital for the continues existence of the cell as it provides it with continuous protection. For instance, if you insert a needle into a cell membrane, it will penetrate without causing it to burst and once the needle is removed, the membrane will seamlessly self-seal. Other reasons why membrane fluidity is important include, allowing membrane fusion; guarantying equal distribution in membrane molecules; enabling separation of the membrane during cell division, and many others.
Factors Affecting Membrane Fluidity
Cell membrane fluidity can be affected by multiple factors and depends in large part on its lipid’s composition. Some of the factors that can affect membrane fluidity are:
Degree of Fatty Acids Saturation
Fatty acids can have saturated or unsaturated tails. Saturated fatty acids have no double bonds, for this reason, they are relatively straight. On the other hand, unsaturated fatty acids contain one or more double bonds and as a result they are crooked.
Due to this bending effect, unsaturated fatty acids increase fluidity, while saturated fatty acids increase rigidity in the cell membrane.
Length of the Fatty Acids Tail
The longer the fatty acid tail the more rigid the membrane will be. On the contrary, short length fatty acids can potentially increase cell membrane fluidity.
Saturated and unsaturated fatty acid tails behave differently under changes in temperature. When the temperature drops, saturated fatty acids become closer and firmer, thus making the membrane more rigid. Contrarily, unsaturated fatty acids, due to their bent structure cannot pack together, so they keep fluid in lower temperatures.
How does Cholesterol increase or decrease flexibility of the membrane?
Cholesterol deserves a separate paragraph with respect to membrane fluidity, as it has a more complicated relationship with the cell membrane. Cholesterol represents the most abundant substance in the cell membrane, around 25-30% and it has the capacity to either increase or decrease membrane fluidity depending on the temperature.
In animal cells, cholesterol acts by inserting itself into a phospholipid bilayer with its polar hydroxyl group. When the temperature rises cholesterol diminishes membrane fluidity by pulling phospholipids together and increasing intermolecular forces. On the other hand, when the temperature drops, cholesterol increases fluidity by keeping phospholipids from packing together.
In this manner cholesterol has the capacity to act as a buffer for the cell membrane, helping it keep fluidity even when the temperature rises or drops. In other words, cholesterol helps to expand the range of temperature in which the cell membrane is fluid and consequently functional.
How Does Cholesterol Affect Membrane Fluidity Conclusion
After reading this article, it should be clear that cholesterol is a vital substance in any animal’s cells. Firstly, it is essential to complete many body functions, secondly, it also plays a huge role in various metabolic pathways, and thirdly, it is fundamental for the functionality of the cell membrane.
With respect to the cell membrane, cholesterol affects membrane fluidity not only by increasing the temperature range in which the cell membrane can continue to function, but it also serves as a barrier, as due to its chemical structure it can fit in spaces between phospholipids, preventing water soluble substances from diffusing across the membrane.