Key Protein Classes and Their Roles in the Human Body
Proteins are long chains of amino acids that form a molecular chain. In this blog post, we will look at the different types of proteins and their functions along with how they can be classified into groups.
The main function of all proteins is to build tissues in our body by binding cells together through its peptide bonds
Proteins have four levels where it can exist: primary, secondary, tertiary and quaternary structure . Primary Structure refers to the order/ sequence of amino acid residues within a polypeptide backbone while Secondary Structure involves hydrogen bonding between atoms which causes folding or bending such as Alpha Helix or Beta Strand formation . Tertiary structure describes proteins' three dimensional shape while Quaternary structure pertains to the formation of complexes between two or more polypeptide chains.
Classes of Proteins
There are five main classes of proteins which can be classified according to their function: Enzymes, Structural Proteins, Transport Proteins, Regulatory Proteins and Hormones. The following is a brief description of each type:
Enzyme proteins catalyse biochemical reactions in the body while some inhibitors stop these enzymes from working.
Structural proteins provide support for cells and tissues while also aiding in movement.
Transport proteins move molecules across cell membranes such as ions, nutrients and waste products.
Regulatory proteins control cellular processes by turning genes on or off.
Hormones act as chemical messengers to communicate between cells.
Importance of Studying Proteins:
Proteins play a vital role in many biological processes and are essential for the body to function properly. By understanding their structure and function, we can gain insight into how they work together to carry out various tasks. This knowledge can be used to develop treatments for diseases or create new drugs that target specific proteins.
Here are Some Best Ways to Study Proteins:
Online resources provide an easy and convenient way to learn about proteins. Simply typing in 'how do proteins work', you will get a plethora of articles that describe their functions, structure and interactions with other molecules.
There are also several apps which can be downloaded onto your phone or tablet for free such as the ‘Proteins Database’ by Hao Wang from Yale University . This app presents users with information on more than 250 different types of proteins.
Learn the basics- It is important to have a thorough understanding of the basics before you delve into more complex concepts.
Taking an online course can be helpful in this regard, especially if it is available for free . Coursera offers numerous courses by universities that have partnered with them which include ‘Cell and Molecular Biology’ from Yale University or 'Bioinformatics: Life Sciences' offered by Johns Hopkins University.
Look up specific amino acids- Amino Acid databases such as Expasy's Peptide Atlas provides information on individual residues such as their three dimensional structure (Cartesian Coordinates), chemical properties (e.g., molecular weight) and other physical data along with protein complexes they are involved in . This will help identify patterns within proteins to find regions/ motifs which are important for their function.
Protein Databases
Once you have a general understanding of proteins, you can then delve into more specific databases that focus on particular proteins or protein families. The two main databases are the Protein Data Bank (PDB) and the National Centre for Biotechnology Information (NCBI). The PDB is curated by the Research Collaboratory for Structural Bioinformatics and contains over 114,000 entries from experimentally determined structures of proteins, nucleic acids and complex assemblies while NCBI houses over 26 million sequences including genes, transcripts, proteins and peptides .
Blast Searching
The most common way to search for information in these databases is through blast searching. This allows you to input a protein sequence and will return all the relevant information from the database related to that sequence.
Structural Homology
Proteins can be classified into families based on their structural homology. This is determined by comparing the amino acid sequences of two or more proteins and looking for regions that are conserved (i.e., have not changed much over time). This allows researchers to identify new proteins, as well as understand how they function and interact with other molecules .
Domain Analysis
Another way to study proteins is through domain analysis. This approach looks at individual domains within a protein and determines their function. By understanding the role of each domain, we can get a better idea of how the protein works as a whole .
Protein Interactions
As proteins are composed of multiple domains, it is important to understand how they interact with one another. This can be done through protein-protein docking simulations which use mathematical models to predict the likely interactions between two or more proteins. These simulations can help identify potential drug targets as well as how best to disrupt those interactions .
FAQs on Types of Proteins and Their Functions
1. What are proteins and what are they made of?
Proteins are essential complex macromolecules found in all living organisms. They are polymers, meaning they are large molecules made up of smaller repeating units called amino acids. These amino acids are linked together by chemical bonds known as peptide bonds to form long chains called polypeptides, which then fold into specific three-dimensional structures to become functional proteins.
2. How are proteins classified based on their molecular shape?
Based on their overall molecular shape and solubility, proteins are broadly classified into two main types as per the NCERT syllabus:
- Fibrous Proteins: These have long, thread-like, or sheet-like structures. They are generally insoluble in water and serve structural or protective roles. Examples include keratin (in hair and nails) and collagen (in connective tissue).
- Globular Proteins: These proteins are folded into a compact, spherical, or globe-like shape. They are typically soluble in water and are involved in metabolic functions. Examples include most enzymes, hormones like insulin, and transport proteins like haemoglobin.
3. What are the main functions of proteins in the body?
Proteins perform a vast array of functions essential for life. Some of the most important functional types include:
- Enzymes: Catalyse biochemical reactions (e.g., amylase digests starch).
- Structural Proteins: Provide support and framework (e.g., collagen and keratin).
- Transport Proteins: Carry substances throughout the body (e.g., haemoglobin transports oxygen).
- Hormonal Proteins: Act as chemical messengers (e.g., insulin regulates blood sugar).
- Contractile Proteins: Enable movement (e.g., actin and myosin in muscles).
- Storage Proteins: Store essential nutrients (e.g., ovalbumin in egg white).
- Defensive Proteins: Protect the body from pathogens (e.g., antibodies).
4. What are the four levels of protein structure?
The structure of a protein is organised at four distinct levels, each building upon the previous one:
- Primary Structure: The unique linear sequence of amino acids in a polypeptide chain.
- Secondary Structure: The local folding of the polypeptide chain into regular patterns, such as the α-helix (a spiral) and the β-pleated sheet.
- Tertiary Structure: The overall three-dimensional folding of a single polypeptide chain, which determines its specific biological function.
- Quaternary Structure: The arrangement and assembly of two or more polypeptide chains (subunits) to form a single, larger functional protein complex, like haemoglobin.
5. What type of protein is haemoglobin and what is its primary role?
Haemoglobin is a globular protein. It is also classified as a conjugated protein because it contains a non-protein part, the 'heme' group, which has an iron atom at its centre. Haemoglobin exhibits a quaternary structure, as it is composed of four polypeptide subunits. Its primary function is to transport oxygen from the lungs to the body's tissues.
6. How does the tertiary structure of a protein determine its biological function?
The tertiary structure refers to the final, specific 3D shape of a protein. This shape is critical because it creates specific regions, such as the active site in an enzyme or a binding site on a receptor. The precise geometry of these sites allows the protein to interact with specific molecules (substrates, hormones, etc.) with high precision. If this 3D structure is disrupted (a process called denaturation), the active site is altered, and the protein loses its biological function.
7. Since there are only 20 common amino acids, does that mean there are only 20 types of proteins?
This is a common misconception. While there are only 20 standard amino acids used to build proteins, they can be arranged in countless different sequences, lengths, and combinations. Think of it like the 26 letters of the alphabet, which can be combined to form an almost infinite number of words and sentences. Similarly, the vast number of possible amino acid sequences allows for the creation of millions of different proteins, each with a unique structure and function.
8. What is the fundamental difference between a globular and a fibrous protein?
The fundamental difference lies in their structure and corresponding function. Fibrous proteins are elongated and insoluble, providing structural support and strength, like the cables in a bridge. An example is collagen. In contrast, globular proteins are compact, spherical, and soluble, carrying out dynamic metabolic functions like catalysis and transport. An example is an enzyme like pepsin, which actively digests food.
9. Why is understanding protein types and functions so important in biology?
Understanding protein types and functions is fundamental to nearly every field of biology. It helps explain how our bodies are built (structural proteins), how they function (enzymes, hormones), and how they defend themselves (antibodies). This knowledge is crucial for medicine in diagnosing diseases caused by faulty proteins (like sickle cell anaemia) and in designing new drugs that target specific proteins.
