Proteins are generally large, complex molecules that play many vital roles in the body. They perform the majority of the work in cells and are needed for the structure, function, and regulation of the body’s tissues and organs. Proteins are composed of many smaller units known as amino acids, that are further attached in long chains. There are around 20 different types of amino acids that can be combined to form a protein. The sequence of amino acids helps to determine each protein’s unique 3-dimensional structure and its specific function. Amino acids are mainly coded by combinations of three DNA building blocks (known as the nucleotides), determined by the sequence of genes.

The number of proteins that are encoded in a genome roughly depends on the number of genes (however there may be several genes that encode RNA of protein, e.g. ribosomal RNAs). Viruses mainly encode a few hundred proteins, archaea and bacteria a few hundred to a few thousand, whereas eukaryotes encode a few thousand to tens of thousands of proteins.

Structure of Proteins

The majority of proteins fold into unique 3D structures. The shape into which a protein generally folds is referred to as its native conformation. However many proteins get folded unassisted, simply via the chemical properties of their amino acids, whereas others need the aid of molecular chaperones to get folded into their native states. Biochemists have often referred to four distinct aspects of a protein’s structure these aspects are discussed below:

Primary structure: this represents the amino acid sequence. This type of protein arrangement is known as polyamide.

Secondary structure: regularly repeating local structures gets stabilized by hydrogen bonds. Some very common examples are the α-helix, β-sheet and turns. Since secondary structures are local, many regions of different secondary structures can be present in the same protein molecule.

Tertiary structure: it represents the overall shape of a single protein molecule and the spatial relationship of the secondary structures to one another. Tertiary structure is stabilized via nonlocal interactions, mainly the formation of a hydrophobic core, but also through salt bridges, hydrogen bonds, disulphide bonds, and also posttranslational modifications. The term “tertiary structure” is very often used as synonymous with the term fold. The tertiary structure is something that controls the basic function of the protein.

Quaternary structure: it represents the structure formed by several protein molecules (i.e. the polypeptide chains), usually known as the protein subunits in this context, which serve as a single protein complex.

Quinary structure: It is the signatures of protein surface that organise the crowded cellular interior. The quinary structure is wholly dependent on transient, yet it is essential, macromolecular interactions that occur inside living cells.

Proteins are not wholly rigid molecules. In addition to these levels of structure, proteins may vary among several related structures whereas they perform their functions. In the context of these functional rearrangements, these tertiary or quaternary structures are generally known as the “conformations”, and transitions between them are known as the conformational changes. These types of changes are often induced by the binding of a substrate molecule to an enzyme’s active site or the physical region of the protein that participates in chemical catalysis. In solution, proteins also undergo some changes in structure due to thermal vibration and the collision with other molecules.

Types of Proteins

Antibodies

Antibodies are specialized proteins that defend the body against antigens or foreign invaders. Their ability to travel through the bloodstream enables them to be utilized by the immune system to identify and defend against bacteria, viruses, and any other foreign intruders in blood. The only way by which the antibodies can counteract antigens is by immobilizing them so that they can be destroyed easily via white blood cells.

Contractile Proteins

These proteins are mainly responsible for muscle contraction and movement. Some examples of these proteins include actin and myosin. Eukaryotes tend to possess huge amounts of actin, that control muscle contraction as well as cellular movement and division processes. Myosin functions to power the tasks carried out by actin by supplying it with energy.

Enzymes

Enzymes are proteins that facilitate and speed up any biochemical reaction, because of which they are often known as catalysts. Some very common enzymes include lactase and pepsin, proteins that are mostly known for their roles in digestive medical conditions and special diets. Lactose intolerance is a result of lactase deficiency, an enzyme that breaks down the sugar lactose found in milk. Pepsin is a digestive enzyme that works in the stomach to break down the proteins in food a shortage of this enzyme may lead to indigestion.

Some of the examples of digestive enzymes are the ones present in saliva such as salivary amylase, salivary kallikrein, and lingual lipase all perform vital biological functions. Salivary amylase is the main enzyme found in saliva and it helps in breaking down starch into sugar.

Hormonal Proteins

Hormonal proteins are the messenger proteins that help in coordinating some bodily functions. Some examples include insulin, oxytocin, and somatotropin. Insulin helps to regulate glucose metabolism by controlling blood sugar levels in the body, oxytocin helps in the contraction of the uterus during childbirth, and somatotropin is a growth hormone that is involved in protein production in muscle cells.

Structural Proteins

These are fibrous and stringy, their formation makes them ideal for supporting various other proteins like keratin, collagen, and elastin.

Storage Proteins

These proteins reserve amino acids for the body until ready for use. Some examples of storage proteins include ovalbumin, which can be found in egg whites, and casein, which is a milk-based protein. Ferritin is another protein that helps in storing iron in the transport protein, haemoglobin.

Transport Proteins

These proteins are also known as carrier proteins that can move molecules from one place to another in the body. Haemoglobin is one of these and is responsible for transporting oxygen through the blood with the help of red blood cells. Cytochromes, it is another type of transport protein, that operates in the electron transport chain as electron carrier proteins.

Conclusion

With this, I would like to conclude that proteins are made up of chains of amino acids, which further fold into unique three-dimensional shapes. Bonding within protein molecules helps in stabilizing their structure, and the final folded forms of proteins are well-adapted for their functions. We, hope that you were able to grasp a clear concept of the topic.