The two fat-based molecules that make up part of the structure of the plasma membrane are:

1. Phospholipids: These are the most abundant component of the plasma membrane. They have a polar head (hydrophilic) and two nonpolar tails (hydrophobic), forming a phospholipid bilayer. This structure allows the membrane to be selectively permeable, allowing only certain molecules to pass through.

2. Cholesterol: This lipid molecule is embedded within the phospholipid bilayer. Cholesterol contributes to the membrane's fluidity and stability, helping it to maintain its structure at different temperatures.