Globular Proteins: Difference between revisions

Globular proteins have a 3D molecular structure that has a shape that is anywhere from a sphere to a cigar.  Usually the structure of a globular protein is divided into three or four levels.  The primary structure is simply the sequence of amino acids forming the peptide chain.  The peptide chain can be folded in an ordered and repetitive fashion, and the structures with ordered and repetitive conformations are called [[Secondary_structure|secondary structures]].  [[Helices_in_Proteins|Helices]], [[Sheets in Proteins|β-sheets]] and [[Turns in Proteins|turns]] are three important types of secondary structures.  Turns are classified as a secondary structure even though their structures are ordered but not repetitive.  The tertiary structure is the overall 3D structure of a globular protein and is produced by folding the helices and sheets upon themselves, and in the process of this folding turns and [[Loops in Proteins|loops]] are formed.  Some globular proteins have a quaternary structure, and it is formed when two or more globular protein molecules (monomer) join together and form a multimeric unit.  [[Hemoglobin]] is a good example of a protein that has a quarternary structure.  The tertiary structure of many globular proteins can be characterized by the number of layers of peptide backbone which are present and the attractive forces which are generated by these layers.<ref name='Garret'>Biochemistry, 4th ed., R. H. Garrett & C. M. Grisham, Thomson/Brooks/Cole, pages 167-170.</ref>  Other important characteristics in the absence of backbone layers are the presence of disulfice bonds, of chelated metal ions or of intrinsically unstructured segments <ref name='Garret'/>.  The objective of this page is to introduce the tertiary structures of globular proteins by illustrating these characteristics of globular proteins.