Difference between Globular and Fibrous Proteins

Proteins are micro-molecules, which perform various functions in the cells of living organism’s body. Proteins are made of amino acid. The shape of a protein molecule is decided by how amino acids are arranged within the molecule.

Depending on the gross structure of the protein molecule, the proteins are classified as −

• Globular proteins
• Fibrous proteins

Read through this article to understand more about each type and the differences between them.

Important Properties of Proteins

To understand the difference between Globular and Fibrous proteins, first go through the following properties, which are considered as parameters to compare the two proteins −

• Amino Acid Sequence − It is the arrangement of amino acids in a protein.

• Shape − Shape of the protein molecule.

• Solubility − If the protein is soluble in aqueous environments.

• Temperature and pH sensitivity − If there is any change in the behavior of a protein due to change in temperature.

• Stability of Structure − If the structure of a protein changes with respect to the changes in its environment.

What are Globular Proteins?

The most common type of proteins which appear in nearly-spherical shape are Globular proteins. They exist in abundance in nature.

Functions of Globular Protein

The shape of a protein and its function are interlinked. Any change in the protein’s shape can result in the change in their function. They act as messengers, transporters, activators, or regulators.

Globular protein has the following functions −

• Enzymes − They catalyze biological reactions in the cells.

• Albumin − It is used to replace lost fluid or blood during trauma and restore them.

• Hemoglobin − It transports Oxygen (O₂) from lungs to blood and facilitates transportof Carbon Dioxide (CO₂) from blood to lungs.

• Ferritin − It is yet another Globular protein that stores iron into cells, which helps make red blood cells healthy.

• Antibodies − They activate immune system and are responsible to keep it healthy.

• Insulin − It regulates sugar or glucose levels in the bloodstream.

There are many more Globular proteins as such, which are vital for normal body functions of a living organism.

Structure of Globular Proteins

Globular protein molecule has a structure of 4 levels −

• Primary − A sequence of amino acids

• Secondary − A spring-shaped helix made of the sequence of amino acids

• Tertiary − A string of the spring-shaped helixes made of the sequence of amino acids

• Quaternary − A bundle of the string of the spring-shaped helixes made of the sequence of amino acids

The resulting bundle is the protein molecule. The following picture depicts how the two proteins are formed from amino acids −

As you can see, Amino Acid Sequence is the fundamental unit of protein structure. The acid forms Peptide Chains and then the chain wraps around to form a Globular protein molecule or Fibrous protein molecule.

What are Fibrous Proteins?

Fibrous proteins are multiple elongated-shaped polypeptide chains that run together in parallel, which are linked together. These proteins are mechanically strong and resistant to dissolving in water. These proteins form the structure of nails, hair, bones, teeth, and cartilage. In vertebrate mammals it is found in claws, fur, and horns. These proteins are damage-tolerant and self-repairing. Keratin, Collagen, Myosin, and Sericin are some examples of fibrous proteins.

Function of Fibrous Proteins

The fundamental function of these proteins is to bind. For example −

• Keratin − It forms the outer layer of skin named as Epidermis. It gives strength to hair, nails, and heals shallow wounds on the skin. It stops brittleness of hair and nails.

• Collagen − It is a Fibrous protein that makes up 35% of the total proteins in the body. It helps bind hard and soft tissues in the body and arrest excess blood loss. It also provides elasticity to skin and keeps joins and bones healthy.

• Myosin − It is found in muscles and controls cell mutation, and muscle contraction and movement.

• Sericin − This protein is produced by silkworms and spiders. When blended with Gelatine, it is used as a binding agent in silk painting, the adheres on the work surface for long.

Structure of Fibrous Proteins

Fibrous protein molecule has a structure of elongated filaments that run in parallel. The filaments are held together tightly with each other via some bonds.

Difference between Globular and Fibrous Proteins

Here are some key differences between Globular and Fibrous Proteins −

Key Factor	Globular Protein	Fibrous Protein
Amino Acid Sequence	They have highly specific amino acid sequence.	These proteins have repetitive sequence of amino acid.
Objective	To carry out almost all cell functions in the body.	To facilitate a solid structure for body parts.
Sensitivity to Temperature and pH	These proteins are highly sensitive to temperature and pH changes.	These proteins are less sensitive to temperature and pH changes.
Shape	The protein molecule is nearly globular or spherical.	The protein molecule is shaped as long filaments bound together.
Solubility	They are soluble in water.	They are not soluble in water.
Stability of Structure	Its structure is unstable when it is exposed to environmental changes such as heat, pH value change, etc.	Its structure is mostly rigid, unaffected due to environmental changes.

Conclusion

Proteins are classified depending on their structure. Both Globular and Fibrous proteins are important for proper functioning of body cells. We also understand that they are noticeably different in some ways such as their amino acid sequence, molecular shape, solubility in water, and sensitivity to environment factors like body temperature.