Cholesterol and the Cell Membrane Structure

Amanda Robb, Emily Lockhart
  • Author
    Amanda Robb

    Amanda has taught high school science for over 10 years. She has a Master's Degree in Cellular and Molecular Physiology from Tufts Medical School and a Master's of Teaching from Simmons College. She is also certified in secondary special education, biology, and physics in Massachusetts.

  • Instructor
    Emily Lockhart

    Emily has taught science and has a master's degree in education.

Learn about the role of cholesterol in the cell membrane. Understand the function of cholesterol in the cell membrane and how it provides structure to a cell. Updated: 01/25/2022

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Cholesterol in Cell Membrane

Cells are the basic units of life and make up all living things. Although there are different types of cells, all cells have some features in common. One example is the presence of a cell membrane, also known as the plasma membrane. The cell membrane is a thin, flexible barrier that separates the cell from the environment. It controls what enters and leaves the cell and allows the cell to be selectively permeable. Cell membranes are important because they allow the cell to create a stable set of internal conditions, called homeostasis. This allows the cell to remain in balance despite a changing external environment.

Cell membranes are primarily made of lipids, macromolecules that are hydrophobic and contain chains or rings of carbon and hydrogen. There are several important lipids that make up the cell membrane, including:

  • Phospholipids
  • Cholesterol
  • Glycolipids

Phospholipids make up most of the cell membrane, with cholesterol added in between. Glycolipids are lipids that have sugar molecules attached to them and can only be found on the external surface of the membrane.

Cell Membrane Structure

The cell membrane is made of two layers of phospholipids, called a phospholipid bilayer. Phospholipids are unique because they are an amphiphile, meaning they have both portions that can interact with water, called hydrophilic, and portions that cannot interact with water, called hydrophobic. The head portion of the phospholipid is made of a phosphate group and is hydrophilic. The tails are made of fatty acid chains and are hydrophobic.


Phospholipid structure

phospholipids


There are four main types of phospholipids in the cell membrane, including:

  • Phosphatidylcholine
  • Phosphatidylethanolamine
  • Phosphatidylserine
  • Sphingomyelin

Each one has a slightly different structure, making them positively or negatively charged. This can impact the way the cell membrane interacts with other molecules. Other phospholipids are also present in smaller quantities. For example, inositol phospholipids are present in very small quantities in the membrane, but are very important in cellular signaling.

Due to energetic favorability, when placed in water the phospholipids will naturally assemble into a bilayer with the heads facing the inside and outside of the sphere and the tails sandwiched in the middle. This shields the hydrophobic tails from interactions with the water. This is the most energetically favorable arrangement of the phospholipids. It also helps create a highly selective barrier where only very small and uncharged molecules, like oxygen or carbon dioxide, can pass directly through the membrane. Other molecules require proteins that can be tightly regulated by the cell.

Cholesterol is a sterol lipid and is made of multiple carbon rings and hydrocarbon chains. Cholesterol is smaller than the phospholipids and fits in between them in the cell membrane. Cholesterol is also an amphiphile, or amphipathic. The hydroxyl group of the cholesterol molecule is hydrophilic and able to fit in with the hydrophilic heads of the phospholipids. The carbon rings are inflexible and hydrophobic and sit in between the tails of the phospholipids.


Structure of cholesterol

structure of cholesterol


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What is The Function of Cholesterol in The Cell Membrane?

What is the purpose of cholesterol in the cell membrane and what does cholesterol do in the cell membrane? The main role of cholesterol in cell membrane is to provide structure and support to the membrane. Cholesterol is situated in the cell membrane in between the phospholipids. The rigid rings of the cholesterol molecule interact with the hydrophobic tails of the phospholipids. This stabilizes them and makes them more rigid as well. This makes the cell membrane less permeable to small molecules.

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Frequently Asked Questions

What is the function of cholesterol?

The function of cholesterol in the cell membrane is to stabilize the interactions between the phospholipids and prevent the membrane from getting too fluid or too flexible.

How does cholesterol stabilize the cell membrane?

Cholesterol stabilizes the cell membrane by forming interactions with the phospholipid tails and heads. This makes their structure more rigid and helps provide stability.

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