Globular proteins also referred to as spheroproteins are the most abundant proteins in nature. 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 structures. Helices, β-sheets and 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 forming the folds. The α-helix and β-sheet regions contain random coils forming irregular structured regions which allow for the polypeptide chain to fold in a unique way. 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.
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 quaternary structure.
Globular proteins are soluble in water and tend to be involved in metabolic functions, as opposed to fibrous proteins which tend to have a structural role. Common globular proteins include:
What You Need To Know About Globular Proteins
- Globular proteins are highly branched or coiled structures and are majorly responsible for transportation of vital nutrients like oxygen through hemoglobin.
- Globular proteins are made up of not only primary, secondary but also tertiary and occasionally quaternary structures.
- The amino acid sequence is irregular in globular proteins.
- Example of globular protein include: Hemoglobin, myoglobin, insulin and enzymes.
- Globular proteins have multiple functions as they are used to form enzymes, cellular messengers, and amino acids.
- Globular proteins are more sensitive to factors such as Temperature and PH.
- They are generally soluble in water and form colloids.
- Globular proteins act as a functional protein performing functions like enzymes as messengers, in the transportation of molecules and regulators.
Fibrous proteins also referred to as Scleroproteins consist of elongated polypeptide chains that run parallel to one another and are stabilized by cross-linkages or have sheet-like structure. These fibers and sheets are mechanically strong and are water insoluble. Fibrous proteins are distinguished from globular proteins by their filamentous, elongated form. The roles of such proteins include protection and structural role by forming connective tissue, tendons, bone matrices and muscle fiber.
Fibrous proteins have amino acid sequences that favor a particular kind of secondary structure which, in turn, confer particular mechanical properties on the proteins. Scleroprotein consists of many super-families including Keratin, Collagen, Elastin and Fibrin. The α keratins are fibrous proteins involved in the structure of hair, finger nails and horns, and their secondary structure is the α-helix with a higher level of structure being the coiled coil.
Fibroins (a β-keratin) are fibrous proteins making up silk and spider webs, and their secondary structure is β-sheets. Collagen is an abundant fibrous protein in vertebrate animals being found in tendons, cartilage and bone, and it has a unique structure. Elastin is an important component of tissues, such as ligaments and skin, and is highly elastic. Its polymeric fibers are made from monomeric units having no secondary structure but having a flexible, disordered structure. The disordered structure permits it to stretch in two dimensions.
What You Need To Know About Fibrous Proteins.
- Fibrous proteins are elongated strand-like structures and are usually present in the form of rods or wires.
- Fibrous proteins have primary and secondary structures.
- Fibrous proteins are made up of regular amino acid strands.
- Examples of Fibrous proteins include: Keratin, Collagen, Fibrin, Actin and Elastin.
- Fibrous proteins act only as structural proteins.
- Fibrous proteins are less sensitive to changes in factors such as changes in temperature and PH.
- They are generally insoluble in water.
- Fibrous proteins help in providing protection and play a structural role in organisms.
Difference Between Fibrous And Globular Protein In Tabular Form
|BASIS OF COMPARISON||GLOBULAR PROTEINS||FIBROUS PROTEINS|
|Description||Globular proteins are highly branched or coiled structures and are majorly responsible for transportation of vital nutrients like oxygen through hemoglobin.||Fibrous proteins are elongated strand-like structures and are usually present in the form of rods or wires.|
|Structures||Globular proteins are made up of not only primary, secondary but also tertiary and occasionally quaternary structures.||Fibrous proteins have primary and secondary structures.|
|Amino Acid Sequence||The amino acid sequence is irregular in globular proteins.||Fibrous proteins are made up of regular amino acid strands.|
|Examples||Hemoglobin, myoglobin, insulin and enzymes.||Keratin, Collagen, Fibrin, Actin and Elastin.|
|Role||Globular proteins are used to form enzymes, cellular messengers, and amino acids.||Fibrous proteins act only as structural proteins.|
|Sensitivity To PH & Temperature||Globular proteins are more sensitive to factors such as Temperature and PH.||Fibrous proteins are less sensitive to changes in factors such as changes in temperature and PH.|
|Solubility||They are generally soluble in water and form colloids.||They are generally insoluble in water.|
|Function||Globular proteins act as a functional protein performing functions like enzymes as messengers, in the transportation of molecules and regulators.||Fibrous proteins help in providing protection and play a structural role in organisms.|