Final answer:
Protein domains are functional and structural units that can fold independently and are subject to molecular evolution. They contribute to the protein's three-dimensional conformation and are distinct from RNA, with varying characteristics such as being hydrophobic in membrane-spanning proteins.
Step-by-step explanation:
Domains within the structure of a protein are functional and structural units that contribute significantly to the protein's overall shape and function. Structural domains often fold independently and can be found across different proteins, indicating their role in molecular evolution. These domains can be swapped in gene families, allowing for the generation of chimeric proteins with new functions. They also play a crucial part in shaping the protein's three-dimensional conformation, which facilitates the correct positioning of amino acids for function, including in interactions with other molecules.
Domains can be hydrophobic, especially in membrane-spanning proteins, where hydrophobic alpha-helical domains interact with the hydrophobic interior of membranes. However, not all domains are hydrophobic; for instance, polar and charged amino acids tend to be found on the surface of proteins that interact with water, showing diversity in domain characteristics. Moreover, domains are not involved in translation nor are they found only in RNA; rather, they are distinct structural features of proteins themselves.