Triglycerides and phospholipids have an important part of their chemical anatomy in common: they both contain fatty acid "tails" that are strongly hydrophobic (high-droh-FOH-bik) or ''water'' (hydr) ''hating'' (phobic).
Each triglyceride molecule has ''three'' (tri-) fatty acid tails attached to a three-carbon molecule called glycerol (GLIH-ser-ahl). Triglycerides make up most of the body fat we humans store as extra energy within some of our cells and tissues. Hundreds of triglyceride molecules tend to group together and form sphere-shaped fat droplets.
Not surprisingly, the hydrophobic fatty acid tails are located deep within the fat droplet, far from any contact with water. But the glycerol end of each triglyceride molecule lies near the surface of the fat droplet, where it may come into contact with water. The fatty acid tails are almost entirely composed of bonded carbon-carbon and carbon-hydrogen atoms, which, having no net electrical charge, do not mix at all with charged H2O!
The phospholipid molecules are an important anatomical component of most cell membranes. The phospholipids are arranged in two columns, with their hydrophobic fatty acid tails mixing together in the middle of the membrane, far from any saltwater. Since they are arranged in ''two'' (bi-) layers, they are often called the phospholipid bilayer (BUY-lay-er) of the membrane.
Each phospholipid molecule has a single polar phosphate (FAHS-fayt)-nitro-gen head end, with both PO4- (phosphate) and N+ charged ends or ''poles.'' The polar phosphate-nitrogen head, bearing positive and negative charges, is considered hydrophilic (high-droh-FILL-ik) or ''water'' (hydr) ''loving'' (phi-lic). Thus, the charged phosphate head of the outer phospholipid layer sticks outward from the cell surface, contacting the watery extracellular fluid, which it so strongly ''loves'' (phil). Similarly, the charged phosphate heads of the inner phospholipid layer project inward to contact the watery intracellular fluid.
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