Final answer:
Fats are the common biological molecules that are always hydrophobic, which means they repel water and do not mix with it. This property differentiates them from proteins, carbohydrates, and nucleic acids, which can be hydrophilic or have varying interactions with water.
Step-by-step explanation:
Understanding Macromolecules and Hydrophobicity
The type of common biological molecules that are always hydrophobic are fats. Unlike proteins, carbohydrates, and nucleic acids, fats are largely nonpolar and do not interact well with water, making them hydrophobic. This characteristic allows them to serve as important storage molecules for energy and as insulation in living organisms.
Macromolecules such as lipids and proteins form the main components of myelin, which is essential in the nervous system for insulating nerve fibers to increase the speed at which impulses are conducted. Molecules are often described in terms of their hydrophilicity or hydrophobicity, which are terms that indicate how they interact with water. Amphipathic molecules, for instance, have both hydrophilic and hydrophobic parts, whereas hydrophobic molecules like fats are water-repellent.
The various functional groups attached to biological molecules determine their overall hydrophobic or hydrophilic nature. Groups such as methyl are hydrophobic, while groups including carboxyl are hydrophilic. Understanding these properties is important when considering the structure and function of biological macromolecules in different cellular environments.