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Lipids are a diverse group of organic compounds that comprise uncharged hydrocarbon chains, making them hydrophobic and insoluble in water.

Based on the number and type of hydrocarbons, lipids can be grouped into three major categories: triglycerides, phospholipids, and steroids.

Triglycerides, often called fats, are made up of glycerol and three fatty acid chains. Lipids are classified as saturated or unsaturated depending on the presence or absence of double bonds in the fatty acid chain.

Unlike triglycerides, phospholipids have only two fatty acid chains attached to a glycerol molecule. The third fatty acid chain is replaced by a charged phosphate group. The fatty acid chains in a phospholipid can also be saturated or unsaturated.

Phospholipids are amphipathic, meaning they contain both hydrophobic and hydrophilic groups.

Their hydrophilic phosphate heads face the water present outside and inside the cell, whereas the hydrophobic tails face each other to form a bilayer, the cell membrane.

The third type, steroids, such as cholesterol, have a unique structure with a carbon skeleton of four hydrocarbon rings and hence, chemically very different from triglycerides and phospholipids.