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What is a Phospholipid? - Structure, Functions & Composition

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  • 0:01 Structure of Phospholipids
  • 0:47 Composition of Phospholipids
  • 1:33 Function of Phospholipids
  • 3:04 Lesson Summary
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Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Your body is made up of cells, but what makes up the cells? Phospholipids are important molecules that provide structure and protection to cells - the very basic units of life.

Structure of Phospholipids

Your body is a complicated machine, so you may be surprised to learn that important biological molecules that make up living things fall into only four main classes: carbohydrates, lipids, proteins, and nucleic acids.

Your cells are surrounded by a very important type of lipid, called phospholipids. Phospholipids consist of a hydrophilic (or 'water loving') head and a hydrophobic (or 'water fearing') tail. Phospholipids like to line up and arrange themselves into two parallel layers, called a phospholipid bilayer. This layer makes up your cell membranes and is critical to a cell's ability to function.

Composition of Phospholipids

Lipids all have one thing in common - they do not mix well with water. You can see this quite well if you try to combine oil and water. No matter how much or how hard you shake them together, they remain separated. This can be useful for organisms. For example, ducks produce lipids in their feathers, allowing the water to roll right off their backs and helping the ducks stay afloat.

Phospholipids are made up of two fatty acids (long chains of hydrogen and carbon molecules), which are attached to a glycerol 'head.' The glycerol molecule is also attached to a phosphate group, and this is the hydrophilic part of the molecule. The 'tail' ends of the fatty acid chains opposite the glycerol is the hydrophobic part of the molecule.

Function of Phospholipids

The most important function for a phospholipid is to form the phospholipid bilayer. In this bilayer, the phospholipids are arranged so that all the hydrophillic heads are pointing outward and the hydrophobic tails are pointing inward. This arrangement comes about because the areas both outside and inside your cell are mostly water, so the hydrophobic tails are forced in.

Since lipids do not get broken down by water, the bilayer provides a barrier around the cell and only lets in certain molecules. Some small molecules, like carbon dioxide and oxygen, pass through the phospholipid bilayer quite easily. This is good because these gases are involved in cellular respiration, which is how your body makes energy from the food you eat.

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