Fibrous and Globular Proteins
Protein is present abundantly in our body. They are compounds formed by amino acids. These amino acids are attached to one another in a long chain-like structure to form a protein. Proteins are polymers or macromolecules made up of smaller structural units. Most functions in our body occur due to the presence of protein. Different types of protein help in the smooth functioning of our body.
Processes like DNA replication, transporting molecules, providing structural balance to cells and organs, response to stimuli, and metabolic reactions are supported by proteins. Proteins are classified on the basis of the sequence of amino acids, and upon the basis of structure and function. The four different levels of a protein structure are- primary, secondary, tertiary, and quaternary structure. On the basis of function, proteins can be classified as fibrous protein, globular protein, and membrane protein. We will discuss the difference between fibrous and globular proteins and the different types of protein.
Types of Proteins
Protein is present in our hairs, nails, muscles, and in the haemoglobin present in our red blood cells. Depending upon the functions of protein we differentiate protein into three types- globular, fibrous, and membrane proteins. These proteins help in the normal functioning of the body. Let us discuss these three types of proteins in detail.
Globular Proteins:
Globular proteins have a spherical structure. These are one of the most abundant types of proteins. Globular proteins help in bodily functions. These proteins are mostly soluble in water and form colloids. They act as enzymes, messengers, transporters, regulators, and sometimes also as structural protein. Haemoglobin is a common globular protein.
Fibrous Proteins:
Fibrous proteins are made up of sheet-like filamentous structures. Fibrous proteins have low solubility in water. These types of protein provide protection and function in the structural role by forming connective tissues, tendons, and muscle fibres. Fibrous proteins are made up of regular amino acid sequences. The most common form of fibrous protein is collagen.
Membrane Proteins:
Membrane proteins as the name suggests are commonly found and are present in the membranes. They interact with biological membranes and therefore are the target of medicinal drugs. These help in providing receptor signals between the internal and external environments of the cell. Also, they help in transporting molecules and allow interaction between molecules. Types of membrane proteins include integral membrane protein and peripheral membrane protein.
Common Proteins and Their Uses
Globular Proteins
Haemoglobin: It is the red colour pigment found in our red blood cells. Haemoglobin is the reason why our blood is red in colour. Its main function is to store and transport oxygen to different parts of the body. The level of haemoglobin should always be maintained in a body as lower amounts of haemoglobin can lead to lower amounts of oxygen and higher amounts of haemoglobin can lead to thickening of the blood which can further lead to heart attack, strokes.
Insulin: Insulin is formed in our pancreas which regulates the level of sugar in our body. It allows glucose to enter our body so that the cells can provide energy.
Fibrous Proteins
Collagen- It is a type of protein that is most abundant in humans (30%). It is made up of amino acids which are further made up of carbon, hydrogen, and oxygen. It gives strength to our various body parts and also protects them. It is a major part of human skin and nails.
Keratin- It is a type of fibrous protein which is present in our hair, nails, and skin. It can also be found in most of the organs inside our body.
What is the Difference between Fibrous Protein and Globular Protein?
Globular protein and fibrous protein are different types of protein that are essential in the proper functioning of a human body. While globular helps in a variety of functions, fibrous proteins are involved in providing structural stability to the organism. Proteins are made up of amino acid strands.
Globular protein and fibrous protein have some differences. These are due to changes in the structure of the protein and the sequence of amino acids. The differences between fibrous protein and globular protein are given below:
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FAQs on Difference Between Globular and Fibrous Protein
1. What is the primary difference between globular and fibrous proteins as per the CBSE Class 12 syllabus?
The primary difference lies in their structure and function. Globular proteins have polypeptide chains that are folded into a compact, spherical shape. They are generally soluble in water and perform dynamic metabolic functions, such as acting as enzymes or transporters. In contrast, fibrous proteins consist of long, parallel polypeptide chains that form strong, rope-like fibres or sheets. They are insoluble in water and primarily serve structural roles, providing strength and support to tissues.
2. How does the shape of globular and fibrous proteins determine their specific biological functions?
The shape of a protein is critical to its function.
- Globular proteins have a complex tertiary structure, creating a specific, compact shape with crevices that form active sites. This precise shape is essential for their function as enzymes (catalysing reactions), antibodies (binding to antigens), and hormones (fitting into receptors). Their spherical shape and solubility allow them to be easily transported in the blood.
- Fibrous proteins have a simple, elongated, and repetitive structure. This arrangement allows them to pack together tightly, forming strong, stable fibres. This makes them perfectly suited for structural roles, such as keratin in hair and nails, and collagen in connective tissues, where strength and insolubility are required.
3. Can you give some important examples of globular and fibrous proteins?
Certainly. Here are some key examples relevant for examinations:
- Examples of Globular Proteins: Insulin (hormone), Haemoglobin (oxygen transport), Albumin (osmotic balance in blood), and most enzymes like Pepsin.
- Examples of Fibrous Proteins: Keratin (in hair, nails, and skin), Collagen (the main protein in connective tissue), Myosin (in muscles), and Fibroin (in silk).
4. What makes globular proteins soluble in water, while fibrous proteins are not?
This difference in solubility is due to the arrangement of amino acid side chains (R-groups) during protein folding. In globular proteins, the polypeptide chain folds in such a way that the hydrophilic (polar) R-groups are positioned on the outer surface, where they can form hydrogen bonds with water molecules. The hydrophobic (non-polar) R-groups are buried in the protein's core, away from the water. In fibrous proteins, the long chains often have a high proportion of hydrophobic amino acids exposed on their surface, which makes them repel water and be insoluble.
5. How does the tertiary structure differ between a typical globular and fibrous protein?
While both protein types have a tertiary structure, its nature is vastly different. The tertiary structure of a globular protein is a complex, non-repetitive, and highly specific three-dimensional folding pattern that results in a compact, globe-like shape. This structure is stabilised by various interactions like hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions. The tertiary structure of a fibrous protein is much simpler and more regular, often consisting of repeating secondary structures (like alpha-helices in keratin or beta-sheets in silk) that are twisted or packed together to form a long filament.
6. Is haemoglobin a fibrous or globular protein, and why?
Haemoglobin is a classic example of a globular protein. Although it has a complex quaternary structure made of four polypeptide subunits, each subunit folds into a compact, spherical shape. It is soluble in the cytoplasm of red blood cells, which is essential for its function of transporting oxygen throughout the body via the bloodstream. Its structure is not long and fibre-like, so it is not classified as a fibrous protein.
7. How does denaturation affect the function of globular versus fibrous proteins?
Denaturation, the disruption of a protein's secondary and tertiary structure by factors like heat or pH changes, has different consequences for each type. For globular proteins, denaturation causes them to uncoil and lose their specific 3D shape. This destroys their active site or binding site, leading to a complete loss of biological activity (e.g., a denatured enzyme cannot catalyse reactions). For fibrous proteins, denaturation also disrupts their structure, but since their function is primarily structural rather than enzymatic, the loss of function manifests as a change in physical properties, such as collagen turning into gelatin upon boiling, losing its tensile strength.
