Amphipathic Definition

Amphipathic is a Greek word, where amphis means “both” and pathy means “feeling”. Compounds which are soluble in water as well as non-soluble are termed as Amphipathic. Thus, they are hydrophobic as well as hydrophilic. They play a vital role as they are important for micelle formation and membrane formation. Thus, plasma membrane makes a barrier so that only selective material can pass through. Thus, maintaining homeostasis and concentration level.

What is Amphipathic Molecule?

Amphipathic molecules possess both hydrophobic and hydrophilic parts. In the hydrocarbon part is a large molecule of carbon which is non- water loving and lipophilic. There is a charge which can be of cations or anions or no charge present on the hydrophilic part with functional groups that are polar. As anions are negative charged the groups present would be sulfonates, phosphates, carboxylates and phosphates. Positive charged groups is ammonium. Thus, the amphipathic molecule has hydrophobic as well as hydrophilic parts.

Amphipathic Characteristics

As the amphipathic molecule possess both hydrophobic and hydrophilic parts, it will have opposite function such as with polar molecules hydrophilic portion will interact. Hydrophobic end will interact with non-polar molecule. Thus, to separate amphipathic molecule into two parts, there should be aqueous as well as non-polar organic solvent.

Examples of Amphipathic Biomolecules

Many amphipathic biomolecule are saponin, cholesterol, lipid, glycolipid, phospholipid and proteins. The amphipathic compound is called the amphiphile.

i. Amphipathic Proteins

Polar and non-polar amino acid sequences are present on these proteins. For example, polar amino acid will be present on hydrophilic end which is formed from protein and on the hydrophobic end non-polar amino acid. In the membranes presence of membrane proteins. As they are amphipathic their hydrophobic portion allows them to interact with the nonpolar region and simultaneously the polar region with the hydrophobic end.

A protein helix with opposing faces is called as amphipathic helix. In the long axis of helix, face in the same direction is called as hydrophilic while the face in the opposite direction is hydrophobic. Proteins hydrophobic and hydrophilic domains can be separated. Protein-protein interaction and self- interaction is possible. Ion channel membrane proteins, apolipoprotein and lung surfactant proteins are example of protein with confirmation.

ii. Phospholipids

b) This molecule are lipid molecule with phosphate group and two fatty acid. the lipid present is glycerol. To the phosphate, which is negatively charged is attached to a glycerol. The phosphate group has the hydrophilic head of phospholipid, which is bound to choline, serine, inositol thus forming phosphatidylserine, phosphatidylinositol and other phospholipid. The tail is made up of two fatty acid which is lipophilic hydrophobic phospholipid tail. There are phospholipid layers in plasma membrane.

As the head is hydrophilic it will interact with polar molecule, whereas the tail is hydrophobic it will interact with non-polar molecule. Thus, the presence of phospholipid in water will make the head exposed to the water and the tails away from the water. Thus, the plasma membrane structure of phospholipids is formed due to amphipathic nature of phospholipid. The heads face the plasma membrane exterior whereas the tails are present in the plasma membrane internally.

iii. Cholesterol

Cholesterol is made up of the hydrophobic hydrocarbon chain and hydrophilic hydroxyl group. It is present in the plasma membrane of animals. To the aqueous medium, hydrophilic head will interact and the to the hydrophobic tail, non-polar solvents will interact.

iv. Glycolipids

Glycolipids are found in the plasma membrane. They are constructed from hydrophilic sugar and attached to hydrophobic lipid tail. In the cell’s outer environment is the carbohydrate which interacts with other sugars and in the lipid, bilayer is the lipid present.

v. Bile- acids

They have a ring like steroid structure with side chain as hydroxyl group with four rings. Around the lipid droplet, bile acid salts will coagulate to form micelle. Thus, forming surfactant. Fats are emulsified so as to stop the coagulation of fats into larger fats.

vi. Saponins

They are present in plants. To keep the herbivore in distant plants release them. It is made up of a glycoside molecule which is hydrophilic and a hydrophobic side chain of steroid. In taste they are pungent and savoury.

Amphipathic Function

i. Membrane Formation

The amphipathic property makes it selectively permeable. An example is plasma membrane which is formed from biomolecules. In plasma membrane, phospholipids has taken a huge space, which have hydrophilic and hydrophobic parts, forming a lipid bilayer. In the lipid bilayer lies the phospholipid tail and the head is positioned at the exterior of the lipid bilayer.

The hydrophobic head and tails are positioned in such a way so as to facilitate movement. Polar molecules cannot pass through the membrane and they have to be modulated, thus, requires a transporter to transport polar molecules but non-polar small molecules can pass. With the hydrophobic lipid bilayer, membrane proteins can interact as they are also amphipathic. Thus, polar and charged molecules can pass through with the help of membrane protein and homeostasis is well maintained.

The movement of molecule is also controlled by the organelles present inside. Cholesterol is present in the animal cell’s plasma membrane and keeps the structure of animal intact and maintains the fluidity of the membrane and thus they do not contain cell wall. Other functions are movement of molecules, conduction of nerve, intracellular transport and signaling of cell. cell to cell interaction, stability are the functions of glycolipid, which is a plasma membrane component. Cell adhesion and cell recognition are the other functions.

ii. Micelle Formation

When the hydrophilic head are with the polar solvent and the hydrophobic head are positioned in the middle, it forms a cluster of molecules it is called micelle. Bile acid can form micelle, due to the amphipathic property. Shape is spherical. Lipid digestion is possible due to micelles in the bile acid. For better absorption, lipids are moved to the edge of the intestinal brush.