Final answer:
Fatty acids are the subunits that make up fats, which, when combined with glycerol molecules, form triglycerides by establishing ester bonds.
Step-by-step explanation:
The subunit that makes up fats are called fatty acids. A fat molecule, often referred to as a triglyceride or triacylglycerol, comprises two main components: glycerol and fatty acids. Glycerol is an organic compound with a backbone of three carbon atoms, each attached to a hydroxyl (OH) group. Fatty acids are long chains of hydrocarbons terminating with an acidic carboxyl group. Carboxyl groups of the fatty acids form ester bonds with the hydroxyl groups of the glycerol molecule during a dehydration synthesis reaction, releasing water molecules. This structure is why fats are also known as triglycerides, as each glycerol molecule can carry three fatty acids. The fatty acids can be saturated, which contain no carbon-to-carbon double bonds, or unsaturated, which include one or more double bonds between carbon atoms.