globular proteins
![Comparison of globular and fibrous proteins.](../../images21/comparison_of_globular_and_fibrous_proteins.jpg)
![Structural comparison of globular and fibrous proteins.](../../images21/globular_and_fibrous_proteins.jpg)
Globular proteins are proteins that consist of long chains of amino acids folded up into complex shapes. Globular proteins serve as, or form important components of, the following:
· Enzymes
· Hormones
· Antibodies
Some globular proteins have a structural role. For example, globular proteins form part of the cell membrane, which has a structural role as well as a role in transporting ions in and out the cell.
The structure of globular proteins has been traditionally discussed in terms of four levels of structure: primary, secondary, tertiary, and quaternary. Two additional levels are now commonly distinguished: motifs and domains.
The other main type of protein, in terms of its structure, is fibrous protein.