Protein is a complex molecule found in all living things. Proteins are nutrient-dense and play an important role in the chemical reactions that keep life going. The importance of proteins was recognised In the early 19th century. Swedish chemist Jöns Jacob Berzelius coined the term protein in 1838, deriving it from the Greek prteios, which means “first position”. Proteins are species-specific, which means they differ from one species to the next. They are also organ-specific; muscle proteins differ from brain and liver proteins within the same organism. As far as the structure and functions of the biomolecule protein are concerned, proteins fold into specific shapes based on the amino acid sequence in the polymer, and the resulting 3D structure is closely tied to the protein function. Proteins can form complex assemblies by interacting with each other and other macromolecules in the body.

Properties of Proteins

• A protein molecule is much larger than a sugar or salt molecule and comprises several amino acids linked together in long chains, similar to beads on a string.

• Proteins contain around 20 distinct amino acids that exist naturally. Amino acid makeup and sequence are comparable in proteins with similar functions.

• Although it is impossible to explain all the functions of a protein from its amino acid sequence, the properties of amino acids can be assigned to proven connections between structure and function.

Types of Proteins

Antibodies, hormone proteins, structural proteins, enzymes, contractile proteins, storage proteins and transport proteins are the seven categories of proteins.

Functions of Proteins

Proteins are involved in a variety of vital biological processes and functions. They are highly adaptable and serve a variety of tasks in the body, as described below:

1. Act as catalysts
2. Transport other molecules
3. Store other molecules
4. Provide mechanical support
5. Provide immune protection
6. Generate movement
7. Transmit nerve impulses 
8. Control cell development and differentiation

Synthesis of Proteins

• Translation is the process through which proteins are made in the body. The process of translating genetic information into proteins takes place in the cytoplasm. 
• During DNA transcription, where DNA is decoded into RNA, genetic instructions are constructed. Ribosomes are cell structures that aid in the transcription of RNA into polypeptide chains, which must subsequently be changed to become functional proteins.
• All proteins, regardless of their function, are made up of amino acids.
• Proteins are made up of a 20-amino-acid chain. The human body can build whatever protein it requires by combining these 20 amino acids. 
• The structural template for most amino acids is that an alpha carbon is attached to one of the following forms:

1. A Hydrogen atom (H)
2. A Carboxyl group (-COOH)
3. An Amino group (-NH2)
4. A Variable group

• As all amino acids have hydrogen, carboxyl group, and amino group bonds, the variable group is largely responsible for variation across the different types of amino acids.

• Dehydration synthesis combines amino acids until peptide bonds are formed. A polypeptide chain is formed when these bonds join a number of amino acids together. A protein is composed of one or multiple polypeptide chains warped into a three-dimensional shape.

Structure of a Protein

A protein’s structure might be globular or fibrous, depending on its function (every protein is specialised). 

• Globular proteins are spherical in form, compact, and soluble.

• Fibrous proteins are typically elongated and insoluble.

Classification of Proteins Based on Structure

Proteins are classified into four structural levels: primary, secondary, tertiary, and quaternary.

• The degree of complexity in a polypeptide chain distinguishes these stages, which determine the form and function of a protein. The primary level describes the most fundamental and rudimentary bonding, whereas the quaternary level describes complex bonding.
• One or more of these protein structural levels can be found in a single protein molecule, and the structure and complexity of a protein determine its function.
• Collagen, for example, has a super-coiled helical form that is lengthy, stringy, strong, and rope-like, making it ideal for supporting the body.
• On the other hand, Haemoglobin is a folded and compact globular protein. Its spherical shape makes it easy to pass through blood vessels.

Conclusion

Proteins are the most abundant biological macromolecules and are found in every cell. They are also the most versatile organic molecules in living systems, with thousands of distinct types ranging in size from small peptides to large polymers. Proteins are polymers of amino acids held together by peptide bonds. The 20 naturally occurring amino acids are the building blocks of proteins. As a result, proteins are amino acid polymers. Proteins are the largest unit of cells in terms of dry weight. Proteins are involved in nearly all cell processes, and each role is assigned to a different type of protein, with duties ranging from general cellular support to cell signalling and movement. There are seven different types of proteins.