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 with turns and [[Loops in Proteins|loops]] forming the folds.  Non-covalent molecular attractions are important forces in maintaining the folded conformation of a globular protein.  For the most part, these attractions are between the atoms of the side chains but can be between the side chains and a bound ligand.  Hydrogen bonds between back bone atoms are important in maintaining secondary structures, and those between side chains are involved in maintaining the tertiary structure.  Examples of finding and visualizing both types in globular proteins are at [[Hydrogen bonds |hydrogen bonds]]. The attractive forces of [[Salt_bridges |salt bridges]] are important in maintaining some tertiary structures, but they also can be involved in the binding of ligands. The Disulfide bond is the one type of covalent bond that can play an important role in maintaining the tertiary structure as well as connecting two or more peptide chains together. Links to sites having structures that illustrate disulfide bonds are at [[Cystine]]. 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.