Understanding What Are Examples of Simple Proteins

December 22, 2025 •

4 min read

By definition, a protein is classified as "simple" if it yields only amino acids or their derivatives upon hydrolysis, without any non-protein components. These fundamental biological molecules include a wide variety of compounds, such as those that provide structural support, store nutrients, and aid in genetic packaging, which are all excellent examples of simple proteins.

Quick Summary

A diverse array of pure protein molecules exists, categorized by their composition of amino acids and distinct biological roles, including transport, structure, and storage.

Key Points

Definition: Simple proteins consist solely of amino acids, yielding only these upon hydrolysis.
Albumin: A key simple protein that maintains osmotic pressure and transports substances in the blood, found in plasma and egg whites.
Globulin: A simple protein found in blood and plants, functioning in immune response (antibodies) and transport.
Histones: Basic simple proteins that organize and package DNA in the nucleus, forming chromatin and chromosomes.
Structural Proteins: Fibrous simple proteins like keratin and collagen provide strength and support to tissues.
Storage Proteins: Plant-based simple proteins like glutelins and prolamins are primarily for nutrient storage.
Distinction from Conjugated Proteins: Unlike conjugated proteins, which have non-protein components, simple proteins are composed purely of amino acid chains.

Defining Simple Proteins

Simple proteins, also known as homoproteins, are one of the three major classifications of proteins based on their chemical composition. Unlike conjugated proteins, which contain a non-protein part called a prosthetic group, simple proteins are made exclusively of polypeptide chains formed from amino acids. Their classification further depends on their solubility in various solvents, such as water, salt solutions, and alcohol, as well as their resistance to denaturation by heat. This pure composition makes them fundamental to countless biological processes across all life forms, from microscopic organisms to complex vertebrates.

Major Classes and Examples of Simple Proteins

Simple proteins are broadly categorized based on their physical properties, including shape and solubility. These properties dictate their function, leading to several distinct classes with numerous examples in nature.

Albumins

Albumins are a group of globular proteins that are highly soluble in water and coagulate when heated. They play crucial roles in maintaining osmotic pressure and transporting molecules in the bloodstream. Notable examples include:

Serum Albumin: The most abundant protein in human blood plasma, responsible for transporting fatty acids, hormones, and drugs, and regulating blood volume.
Ovalbumin: Found in egg whites, it makes up about 55% of the egg's total protein content and is a key nutritional protein.
Lactalbumin: A protein found in milk, also serving as a nutrient source.

Globulins

Globulins are globular proteins that are insoluble or sparingly soluble in pure water but dissolve readily in dilute salt solutions. They have diverse functions, including immune response and transport. Examples include:

Immunoglobulins: Also known as antibodies, these are a class of gamma globulins produced by plasma cells to neutralize pathogens.
Serum Globulins: Other globulins found in blood plasma that transport lipids, hormones, and assist with blood clotting.
Legumin: A globulin found in the seeds of peas and other legumes, serving as a storage protein.

Glutelins

Glutelins are plant proteins found in cereals like wheat and rice. They are insoluble in water and saline but soluble in dilute acids and alkalis. A well-known example is glutenin from wheat, which is a major component of gluten and contributes to the elasticity of dough.

Prolamins

Another group of plant storage proteins, prolamins are characterized by their solubility in 70-80% aqueous alcohol but insolubility in water. They are rich in proline and glutamine amino acids. Examples include:

Gliadin: Found in wheat, it is another component of gluten.
Zein: The primary prolamin found in maize (corn).

Histones

Histones are small, highly basic proteins found within the cell nuclei of eukaryotic organisms. They are rich in the basic amino acids lysine and arginine, giving them a positive charge. Their primary function is to package and organize the vast amount of DNA into structural units called nucleosomes, which in turn form chromatin and chromosomes. There are five main types of histones: H1, H2A, H2B, H3, and H4.

Protamines

Protamines are very small, arginine-rich basic proteins that replace histones late in the haploid phase of spermatogenesis. They allow for even denser packaging of DNA in the sperm head. Examples include salmine from salmon sperm and clupeine from herring sperm.

Scleroproteins (Fibrous Proteins)

Also known as albuminoids, these are insoluble, fibrous proteins that play structural roles in the body. They are long protein filaments that provide support and protection. Key examples include:

Keratin: The primary structural protein of hair, nails, and the outer layer of skin.
Collagen: The most abundant protein in mammals, a major component of connective tissues like tendons, cartilage, and bone.
Elastin: A fibrous protein found in tissues that require elasticity, such as the lungs and blood vessel walls.

Comparison of Simple vs. Conjugated Proteins

To better understand simple proteins, it's helpful to contrast them with conjugated proteins. The key difference lies in their composition, which directly influences their function and properties.


Feature	Simple Proteins	Conjugated Proteins
Composition	Made only of amino acids.	Contain amino acids plus a non-protein part (prosthetic group).
Hydrolysis Product	Yields only alpha-amino acids.	Yields amino acids and a non-protein component.
Examples	Albumin, Globulin, Histone, Keratin.	Hemoglobin (protein + heme group), Glycoproteins (protein + carbohydrate).
Function	Structural support, storage, transport (e.g., albumin).	Specialized functions like oxygen transport (hemoglobin) or immune recognition (glycoproteins).
Structure	Can be fibrous (keratin) or globular (albumin).	Complex structures influenced by the prosthetic group.

The Critical Importance of Simple Proteins

The functionality of simple proteins is a testament to the elegant complexity of biology. From the structural integrity provided by fibrous proteins like collagen to the crucial transport and immune functions of albumins and globulins, these pure polypeptide chains form the workhorses of the cellular world. Histones, by organizing DNA, are fundamental to genetic regulation, while protamines ensure efficient DNA compaction in sperm. Their diverse roles highlight why understanding simple proteins is a cornerstone of modern biochemistry.

Conclusion

The world of simple proteins is vast and essential, covering everything from the building blocks of our hair and skin to the molecules that regulate our blood volume and organize our genetic material. Examples of simple proteins like albumins, globulins, and histones demonstrate that even without additional components, a single chain of amino acids can perform incredibly diverse and critical functions. Their classification by solubility and function helps us categorize these vital molecules and appreciate the fundamental importance they hold in all living organisms. For further information on protein classification, an excellent resource can be found at Britannica.

Frequently Asked Questions

The primary difference is that simple proteins are made exclusively of amino acids, while conjugated proteins contain amino acids along with a non-protein component called a prosthetic group.

No, simple proteins are found in both plants and animals. For example, albumins, globulins, histones, and protamines are common in animals, while glutelins and prolamins are plant-based storage proteins.

Histones are fundamental to genetic regulation. Their main function is to package and organize the long strands of DNA into compact structures called nucleosomes, allowing them to fit inside the cell nucleus.

Albumin and globulin differ in their solubility. Albumin is highly soluble in water, while globulin is insoluble in pure water but dissolves in dilute salt solutions. They also have different functions, with albumin maintaining osmotic pressure and globulins including antibodies and transport proteins.

Common examples of fibrous simple proteins, also known as scleroproteins, include keratin (found in hair and nails) and collagen (found in connective tissues, bones, and tendons).

While proteins are not a primary energy source, the amino acids from digested simple proteins can be catabolized for energy if necessary, though their main roles are structural, transport, and enzymatic.

Glutenin and gliadin are classified as simple proteins (specifically glutelins and prolamins, respectively) because they consist only of amino acid chains and contain no additional non-protein components.

Albuminoid is an older term for scleroproteins or fibrous simple proteins, which are insoluble in water and play structural roles.