A phospholipid is similar to a triglyceride except instead of one of the fatty acid groups it has a phosphate group. A glycolipid has a nonpolar section made of a fatty acid chain and hydrocarbon chain, and a polar section made of a sugar molecule. Phospholipids and glycolipids both have a polar and nonpolar section.

Triglycerides are the main form of stored energy in animals and are a key part of human metabolism. Understanding the structure of triglycerides is crucial as they are a significant contributor to various biological functions. A triglyceride is composed of one glycerol molecule bonded to three fatty acid tails.

The glycerol operates as a backbone, with each of its three hydroxyl (-OH) groups forming an ester linkage with the carboxyl (-COOH) group of a fatty acid during a dehydration synthesis reaction. This means that for each bond, a water molecule is removed, effectively joining the fatty acids and glycerol.

These long fatty acid chains can vary in length and in the number of double bonds present, influencing the triglyceride’s properties such as melting point and solidity at room temperature.

Amphipathic molecules possess both hydrophilic (water-loving or polar) and hydrophobic (water-fearing or nonpolar) parts, which allow them to interact with diverse substances. This dual nature is vital for the formation and function of cell membranes.

The polar section, often referred to as the 'head', attracts water, while the nonpolar 'tails', typically made up of long hydrocarbon chains, repel water. The arrangement of these molecules in biological systems leads to the formation of bilayers, as seen in cell membranes, with the heads pointing outward towards the water environments on either side, and the tails pointing inward, avoiding water.

The cell membrane, also known as the plasma membrane, is predominantly made of phospholipids arranged in a bilayer layout. This strategic arrangement is fundamental to the membrane's function as a semipermeable barrier controlling entry and exit of substances.

In addition to phospholipids, the cell membrane comprises proteins that serve various roles, including transport, communication, and attachment points. Cholesterol molecules also scatter within the bilayer, adding fluidity and stability to the structure. Glycolipids, present on the extracellular surface of the cell membrane, contribute to cell recognition and signaling.

Dehydration synthesis is a chemical reaction type central to many biological processes, including the formation of triglycerides and phospholipids. During this reaction, two molecules are covalently bonded together with the elimination of a water molecule.

In the context of lipid synthesis, dehydration synthesis involves the bonding of fatty acid chains to glycerol or the addition of a phosphate group in phospholipids. This reaction is facilitated by enzymes in biological systems and is a form of condensation reaction where water is the byproduct of joining molecular components.

Differentiating between polar and nonpolar sections within molecules is pivotal to comprehending why amphipathic molecules, such as phospholipids and glycolipids, function as they do. Polar sections of these molecules can form hydrogen bonds and interact with water.

They are often involved in chemical reactions or creating links with other molecules in a water-based environment, like blood or cellular cytoplasm. Conversely, nonpolar sections mainly consist of carbon and hydrogen atoms linked by nonpolar covalent bonds and exhibit no difference in electrical charge across the molecule. These hydrophobic sections tend to cluster away from water, preferring to interact with oils or other nonpolar substances.