Phospholipids are any of numerous phosphorus-containing intricate lipids (such as lecithin’s and phosphatidylethanolamines) that are originated from glycerol and are crucial components of the membranes of cells and intracellular organelles and vesicles.


Phospholipids commonly consist of a hydrophilic polar phosphate head and a hydrophobic tail of two fatty acids. In aqueous environments, phospholipids usually form semipermeable bilayers in which the hydrophilic heads point exterior and the hydrophobic tails point interior toward each other.


The structure of the most common class of phospholipids, phosphoglycerates’, is stationed on glycerol, three-carbon alcohol with the formula:


Following are some examples of phospholipids

  • Main phospholipids

  • Phosphatidic acid (phosphatidate PA)

  • Phosphatidylethanolamine (cephalin) (PE)

  • Phosphatidylcholine (lecithin) (PC)

  • Phosphatidylserine (PS)

Formation of phospholipids

Phospholipids are mostly assembled from glycerides by replacing one of the three fatty acids with a phosphate group with some other molecule fastened to its end. The other configuration of phospholipids is sphingomyelin, which is emanated from sphingosine alternatively of glycerol.

Phospholipid bilayer in the plasma membrane

The cell membrane is created mainly of phospholipids, which comprise fatty acids and alcohol. The phospholipids in the cell membrane are systemized in two layers, called a phospholipid bilayer. Each phospholipid molecule possesses a head and two tails. The head “loves” water (hydrophilic) and the tails “hate” water (hydrophobic). The water-hating tails are on them onto the surface, while on the contrary, the water-loving heads end outside, alternatively the cytoplasm or the fluid that are adjacent to the cell.

Molecules that are hydrophobic can freely render across the cell membrane, if they are sufficiently minute, as long as they are water-hating like the innards of the membrane. Small lipids and steroids are hydrophobic and can voluntarily navigate the membrane. Molecules that are hydrophilic, on the other hand, cannot perambulate via the cell membrane at the minimum not without aid for they are water-loving like the external of the membrane and are consequently shut out from the inside of the membrane. Hydrophilic molecules such as glucose and ions like Na+ and K+ necessitate the assistance of particular proteins to pass through the membrane.

Membrane fluidity

A cell’s plasma membrane accommodates proteins and other lipids (such as cholesterol) inside the phospholipid bilayer. The organic layer keeps on solution being of the unsaturated hydrophobic tails, which cease phospholipid particles from building a solid.

If a drop of phospholipids is set down in the water, the phospholipids impulsively mould a construction known as a micelle, with their hydrophilic heads aligned on the way to the water. Micelles are lipid molecules that organize themselves in a circular appearance in an aqueous solution. The surfacing of oligomers is a reaction in which both polar and non-polar section in the essence of fatty acids, which means that they carry a couple of hydrophilic and hydrophobic to an extent.

Fluid mosaic model

The fluid mosaic model, to begin with, was put forward in 1972. This model has uncoiled slowly, yet, it still supplies a useful representation of the creation and behaviour of membranes in many cells.

In accordance with the fluid mosaic model, the plasma membrane is a patchwork of building blocks principally, phospholipids, cholesterol, and proteins that shift readily and facilely in the plane of the membrane. Particularly, a sketch of the membrane (like the one below) is wholly an illustration of an effective procedure in which phospholipids and proteins are frequently creeping past reciprocally.

Fascinatingly ample, this fickleness means that if you slot a very thin pointer into a cell, the membrane will plainly part to dislocate in the vicinity of the pointer; once the pointer is detached, the membrane will slide back together jointly.

The key role of the plasma membrane is lipids (phospholipids and cholesterol), proteins, and carbohydrate species that are embedded in some of the fats and amino acids.

A phospholipid is a lipid formed of glycerol, two fatty acid tails, and a phosphate-associated head group. Biological membranes basically composed of two layers of phospholipids with their tails inside, this change is known as the phospholipid bilayer.

Cholesterol, one more lipid comprised of four amalgamated carbon rings, is present alongside phospholipids in the centre of the membrane.

Membrane proteins may expand pathways into the plasma membrane, navigate the membrane completely, or be roughly hooked to its inside or outside face.

Carbohydrate groups are on the outside of the plasma membrane and are connected to proteins, to create glycoproteins, or lipids, forming glycolipids.

The ratio of proteins, lipids, and carbohydrates in the plasma membrane alternate between varying types of cells.

An individual cell, for all that, for the formation by a mass the number of proteins are about 50 per cent, lipids (of all types) include 40 per cent, and the remaining 10 per cent from carbohydrates.

Classification of Phospholipids

Phospholipids are classified into two types.

  1. Glycerophospholipids (or) Phosphoglycerides that comprise glycerol as alcohol.

  2. Sphingophospholipids that comprise sphingosine as alcohol.


These are the significant lipids that appear in biological membranes. They occur in every plant and animal cell. They are appreciably existing in the heart, brain, kidney, egg yolk and soya bean. The essential glycerophospholipids are lecithin, cephalin, phosphatidylinositol, cardiolipin and plasmalogen.

The lecithin accommodates glycerol, fatty acids, phosphoric acid and choline (nitrogenous base). Lecithins normally consist of a saturated fatty acid at a1 position and an unsaturated fatty acid at β position.

The cephalin carries glycerol, fatty acids, phosphoric acids and ethanolamine as a nitrogenous base.

Phosphatidylinositol holds hexahedral alcohol called inositol.

Plasmalogens contains an ether link in a1 position rather ester link. The alkyl radical is unsaturated alcohol and they are present in the brain and nervous tissue.


These are found in the plasma membrane and myelin sheath. They are amphipathic lipids containing polar heads and non-polar tails. They have amino alcohol called sphingosine. It is fastened to a fatty acid by an amide linkage to form ceramide. Ceramide is associated with phosphorylcholine to make sphingomyelin, which is a crucial member of sphingophospholipids.

Properties of Glycerophospholipids

Glycerophospholipids are white waxy material, which develops into the dark when bare to air and light, owing to autoxidation and breakdown. This is due to the existence of unsaturated fatty acids in the molecules.

  • They are dissolved in alcohol and other fat solvents excluding acetone.

  • They are hygroscopic and merge completely with water to form cloudy, colloidal and slimy solutions.

  • They do not have an explicit melting point and deteriorate when excited.

  • They are easily hydrolyzed by boiling with acids and alkalis to their components.

  • They are hydrolyzed by enzyme phospholipase to various constituents.

Properties of sphingophospholipids

  • They are white crystalline materials.

  • They form a lustrous suspension in water.

  • They are irresolvable in fat solvents like ether and acetone.

  • They are firm in air and light.

Types of phospholipids

In the plasma membrane of several primate cells, four essential phospholipids are present i.e. phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin.

1.Phosphatidylcholine (lecithin)

These are Glycerophospholipids together with choline. These are the most important phospholipids of the cell membrane having both structural and metabolic purposes. Dipalmitoyl lecithin is abundant phosphatidylcholine detected in the lungs, manufactured by lung type II epithelial cells. It executes the task of a lung surfactant and is important for normal lung function. It reduces surface area tension in the alveoli, hence preventing alveolar fall (adherence of the inner surface areas of the lungs).

2. Phosphatidylethanolamine (Cephalin)

They differ from lecithin in containing nitrogenous base ethanolamine rather than choline. Thromboplastin (coagulation factor III), which is required to initiate the clotting process, is composed of particularly cephalins.

3. Phosphatidylserine

It contains the amino acid serine instead of ethanolamine and is present in many tissues.

4. Sphingomyelin

Sphingomyelin is the exclusive phospholipid in membranes that are not derived from glycerol. Relatively, the alcohol in sphingomyelin is amino alcohol i.e. sphingosine. In sphingomyelin, the amino group of the sphingosine is attached to fat to provide ceramide (sphingosine fatty acid complex). Moreover, the primary hydroxyl group of sphingosine is esterified with phosphorylcholine. Sphingomyelin is between the main compositional lipids of membranes of nerve stuff.

Reactions of phospholipids

At the point of sn3, the third hydroxyl part of glycerol reacts with phosphoric acid give rise to phosphatidate. Common phospholipids, extensively spread in nature, are assembled by further reaction of the phosphate group in phosphatidate with an alcohol, such as serine, ethanolamine, choline, glycerol, or inositol.

Importance of phospholipids

  • They create the structural constituents of the membrane and adjust the membrane absorptive nature.

  • They perform a crucial role in cellular respiration.

  • They take part in the permeability of fat from the intestine.

  • They behave as surface tension reducing agents.

  • They are important constituents of bile where they perform the function of detergents and aid in the dissolution of cholesterol.

  • They also participate in blood clotting.

  • They secure the neuronal fibres of the myelin sheath.

  • They are participating in the exchange of hormones with receptors.

  • They behave as oleophilic factors and protect from the evolution of the fatty liver.

  • They aid in the altered transmission of cholesterol.

Functions of Phospholipids

  • They check the permeability of the membrane as well as activate a few membranes covering enzymes.

  • Phospholipids are enclosed nerve impulse (like the plastic or rubber covering around an electric wire) from the nearby arrangement, e.g., sphingomyelins function as electrical insulators around the myelin sheath.

  • Phospholipids are a necessary element of lipoproteins.

  • Phospholipids act as lipophilic features. The lipophilic is the part that protects the sebaceous bile, i.e., the expansion of fat bile.

  • These are better breaking compounds that resist the digestion of fatty acids.

  • Thromboplastin (coagulation factor III), which is required to begin the clumping action, is specifically made up of phospholipid found especially in the cells of systema nervosum.

  • Phospholipid (lecithin) acts as a lung surfactant, which avoids alveolar collapse.

  • Phosphatidylinositol functions as a second messenger for the task of particular hormones.

  • In mitochondria, cardiolipin is required for supreme roles of the electron transportation procedure.

  • Plasminogen (platelet-activating element) is linked with platelet accumulation and degranulation.

Acting as a surfactant

Pulmonary surfactant is a blend of lipids, primarily phospholipids, and protein that permit breathing with less work. Surfactant phospholipids are manufactured in type II epithelial cells of the lung. The lipids and surfactant proteins are collected in intracellular storage organelles, called lamellar bodies, and are eventually discharged into the alveolar space. Surrounded by this extracellular space surfactants experience various modifications. First, the lamellar bodies unwind to make a greatly assembled lattice-like lipid: protein structure tubular myelin. Second, the arranged construction, in specific tubular myelin, uptake to form a lipid at the air-liquid configuration of the alveoli. It is, in point of fact, this surface tension lowing film that is responsible for the physiological character of surfactant, to avoid lung fall down and permit proficiency of inflation. Third, the surface film is transformed into a minute vesicular arrangement. Eventually, these little vesicles are adopted by the type II cells for reusing and deterioration and by alveolar macrophages for degradation.

Tests for phospholipids

Below are a few tests for phospholipid

Simplified acid Haematein test

Colourimetric method

Simplified acid Haematein test

The acid haematein test of Baker was analyzed by the successive manner: Tissues were fastened in either formal-calcium or formal-calcium-cadmium, frozen-sectioned in a cryostat, aromatized with potassium dichromate, washed in water, spotted in acid haematein solution, washed in water one more time, transformed in borax-ferricyanide, dehydrated in alcohols, removed in xylene, and eventually arranged in balsam. The process demands only 2 days rather than the 6 days important for the authentic test of Baker. The technique darkens phospholipid in mitochondria and in more cellular elements and is suggested chiefly for mitochondria.

Colourimetric method

Phospholipids are accelerated with trichloroacetic acid and react to phosphate with sulphuric acid and perchloric acid. Inorganic phosphorus available as phosphate makes a phosphomolybdate complex with molybdic acid. The complex is decreased by stannous chloride to a blue colour which can be calculated calorimetrically.

Frequently Asked Questions

Q.1 How do phospholipids affect the body?

Phospholipids play an important role in body health and promote the involvement and distribution of essential alpha-linolenic fatty acids.

Q.2 Can you take too many phospholipids?

The daily uptake of more than 30 grams of phospholipids causes dysentery, sickness, cough up.

Q.3 Are phospholipids good for the heart?

Some plasma phospholipids are saturated fatty acids linked with an increased rate of cardiac disorder and increased blood pressure. It is a big danger for the failure of the heart.

Q.4 How many phospholipids should I take daily?

The uptake of phospholipids is more or less 2-8 grams every day.

Q.5 When phospholipids are mixed with water Their?

When phospholipid is situated in water, it forms a lipid molecule called micelles that arrange itself in a globular form in an aqueous solution.

Q.6 What are phospholipids composed of?

Phospholipids are comprised of two alcohol, one or two fatty acids, and a phosphate group. Phosphate group and one alcohol are present on one polar end of the molecule i.e. it is attracted towards the water and possesses an electric charge.

Q.7 What is the head of a phospholipid?

A phospholipid has two parts: a head and a tail. The head molecule consists of a phosphate group and is hydrophilic i.e. destroyed in water. While the tail part of the molecule is made up of two hydrophobic fatty acids i.e. do not destroy in water.


Phospholipids are the important biological components of the human body that plays an important role in providing 9 calories/gram of energy and maintaining the fluidity of membranes. Moreover, phospholipids are the best source of strengthening the body besides proteins and carbohydrates. Besides it, they are also of great use in daily life as oil and ghee.

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