Phospholipids or Phosphatides are amphiphilic (a chemical compound containing both lipophilic or “water-loving” and hydrophilic or “water-fearing” properties) lipids. Phospholipids are composed of a glycerol and phosphate group (hydrophilic head) and two fatty acids (hydrophobic tails).
Hydrophilic (water-loving polar) properties of phospholipids found in the head section attract water molecules and bind readily through hydrogen bonds. The fatty acid or the hydrophobic tail of a phospholipid is nonpolar, making it insoluble to water. Phospholipids form a bilayer in water where the hydrophilic heads of the molecules are exposed to the water, while the hydrophobic tails interact with each other.
Contents
- 1 What makes up a phospholipid?
- 2 What happens when you add phospholipid to water?
- 3 Why do phospholipids form a bilayer when mixed with water?
- 4 Which end of a phospholipid can interact with water?
- 5 What part of a phospholipid is like water?
- 6 Are phospholipids hydrophobic, hydrophilic, or amphipathic?
What makes up a phospholipid?
The general structure of phospholipid is composed of:
- One glycerol, a simple trihydric alcohol compound
- Two fatty acids or carboxylic acids
- One or more inorganic phosphate group modified by an alcohol
Through esterification (a chemical reaction of a carboxylic acid with alcohol), two long chains of fatty acids are attached to two carbons of the glycerol molecule. The Phosphate group is attached to the third carbon of the glycerol backbone. This is only the precursor of a phospholipid, phosphate has to be modified by alcohol compounds such as serine, ethanolamine, choline, inositol to complete the whole structure of phospholipids.
A phospholipid has two parts, the head, and the tail. The head contains the glycerol and phosphate group, which are polar and hydrophilic, while the tail contains two fatty acids that are nonpolar and hydrophobic. These two properties of phospholipid make its amphiphilic properties.
What happens when you add phospholipid to water?
Phospholipids do not mix well with water because of its amphipathic properties (both water fearing and water loving properties). No matter how you shake it, it will not mix totally. Phospholipids have different formations depending on the amount of phospholipids concentration in water. If you put a small drop of phospholipid in the water, it forms a micelle (a spherical form in aqueous solutions as a response to the amphipathic nature of molecules). The hydrophilic polar heads turn toward the water, while the hydrophobic nonpolar tails aggregate inside and interact with each other. As phospholipids saturate the water, micelles will float to the surface and form an oily film. The polar head faces down the water, and fatty acids will stick up to the surface.
As more phospholipid saturates the water, it will result in a formation of a bilayer, allowing two adjacent polar layers to be in contact with water while simultaneously allowing all the fatty acid tails to bury itself in an oily layer away from the water. If the water is fully drenched with phospholipids, it would naturally form spherical bilayers of phospholipids that had water suspended inside and outside, which is similar to biological cell membranes and intracellular organelles.
Why do phospholipids form a bilayer when mixed with water?
In high phospholipids concentration in water, it will spontaneously form a lipid bilayer. Fatty acid (hydrophobic) chains meet at the center to stay away from the water. Phosphate (hydrophilic) ends stay in contact with water forming like a barricade to prevent fatty acids from having contact with water. The phospholipid bilayer is the same mechanism that we found in biological cell membranes and intracellular organelle. Phospholipids form in a spherical shape in the cell membrane. The inner and outer surfaces are phosphate groups, while the fatty acid chains gather in the middle.
Which end of a phospholipid can interact with water?
The phosphate head is negatively charged, making it polar and hydrophilic (water-loving). Thus, the phosphate heads tend to be attracted by polar covalent water molecules through hydrogen bonding. In contrast, the phospholipid tails are uncharged, non-polar, and hydrophobic. Hence, water molecules repel phospholipid tails.
What part of a phospholipid is like water?
Just like water (H2O), phospholipids have polar properties. The head of phospholipids is polar and hydrophilic. Thus, phospholipids can also attract polar water molecules through hydrogen bonds. However, unlike water, phospholipids interact more with non-polar molecules in chemical reactions and are less likely to interact with other polar molecules due to their amphipathic properties.
Are phospholipids hydrophobic, hydrophilic, or amphipathic?
Phospholipids are amphipathic, hydrophobic, and hydrophilic. But how does that happen? Phospholipids have amphipathic nature which means, it has both hydrophobic and hydrophilic properties. Having both properties is driven by the structural component of phospholipid: the fatty acid tail and the phosphate group head. One is hydrophilic and the other is hydrophobic.
Phospholipids’ hydrophobic properties repel water. The long chain of fatty acids is nonpolar and does not interact with water. They usually bury themselves away from the water and other polar molecules. Phospholipids’ hydrophilic properties are driven by the phosphate head. It is negatively charged and polar. This property makes the head attracted to water polar covalent molecules through hydrogen bonds. These unique properties of phospholipids make it essential to the existence of all biological organisms on this planet.
