What is Biotin Made Of? Exploring the Chemical Composition and Sources

December 12, 2025 •

3 min read

As a vital B-vitamin (B7) found in every living cell, biotin plays a critical role as an enzyme cofactor in numerous metabolic processes. To understand its function, we must first break down the question, 'what is biotin made of?' at a molecular level.

Quick Summary

Biotin is an organic, water-soluble compound with the chemical formula C10H16N2O3S. It is defined by its fused ring structure and valeric acid side chain, comprising carbon, hydrogen, nitrogen, oxygen, and sulfur atoms essential for its biochemical role.

Key Points

Elemental Composition: Biotin's molecular formula is C10H16N2O3S, meaning it is made of carbon, hydrogen, nitrogen, oxygen, and sulfur atoms.
Molecular Structure: Its core structure features two fused rings—a ureido ring and a tetrahydrothiophene ring—plus a valeric acid side chain.
Natural Production: Biotin is synthesized by plants, bacteria, and some fungi; humans cannot produce it and must obtain it from dietary sources.
Dietary Sources: The vitamin can be found in a variety of foods, including egg yolks, liver, legumes, and nuts.
Biochemical Function: The chemical structure allows biotin to act as a crucial coenzyme, primarily for carboxylase enzymes involved in vital metabolic processes.
Natural vs. Synthetic: The chemical composition of natural biotin found in foods and synthetic biotin in supplements is the same, though their delivery forms differ.

Biotin's Chemical Blueprint

At its core, biotin is an organic molecule, meaning it is built around a framework of carbon and hydrogen atoms. Its precise chemical formula is C10H16N2O3S, which indicates the specific number of atoms of each element that compose it. The intricate arrangement of these atoms gives biotin its unique properties and function. The molecular makeup consists of two fused rings—a ureido ring and a tetrahydrothiophene ring—connected to a side chain.

The ureido group, containing nitrogen (N), carbon (C), and oxygen (O) atoms, is one of the molecule's most significant functional components. This ring is crucial for the vitamin's metabolic function, specifically for carrying carbon dioxide in carboxylation reactions. Fused to this is the sulfur-containing tetrahydrothiophene ring, which gives biotin its classification as an organosulfur compound. The final key feature is a valeric acid side chain, a five-carbon carboxylic acid chain, which is essential for biotin's covalent attachment to enzymes in the body.

The Atom-by-Atom Breakdown of Biotin

To provide a clearer picture of biotin's composition, here is a list of the elements and their roles:

Carbon (C): The backbone of all organic compounds, carbon forms the structural skeleton of biotin's fused rings and its valeric acid side chain.
Hydrogen (H): Hydrogen atoms saturate the carbon skeleton, contributing to the molecule's overall structure and stability.
Nitrogen (N): Two nitrogen atoms are found within the ureido ring, participating in the critical carboxylation reactions for which biotin is known.
Oxygen (O): Oxygen is present in the carbonyl group of the ureido ring and the carboxylic acid group of the side chain, both important for biotin's biochemical activity.
Sulfur (S): A single sulfur atom is located within the tetrahydrothiophene ring, a distinguishing feature that classifies biotin as an organosulfur compound. This sulfur is inserted during biosynthesis in a process involving biotin synthase.

Synthesis and Cellular Origins

Unlike many other vitamins, biotin cannot be synthesized by mammals, who must acquire it through diet. The synthesis of this complex molecule is carried out primarily by bacteria, plants, and some fungi. This complex biosynthetic pathway starts with precursors like alanine and pimeloyl-CoA. In the final step, an enzyme called biotin synthase inserts the sulfur atom into a precursor molecule called dethiobiotin to complete the biotin structure. This intricate synthesis process ensures that biotin is available in the food chain for animals and humans who cannot produce it themselves. Small amounts of biotin can also be synthesized by bacteria residing in the large intestine, though how much is absorbed by the human host is still under investigation.

Natural vs. Synthetic Biotin

Whether sourced from food or produced in a laboratory, the chemical makeup of D-(+)-biotin is identical. However, the context of natural vs. synthetic sources can impact delivery and efficacy.


Feature	Natural (Food-Derived) Biotin	Synthetic (Supplement) Biotin
Composition	D-(+)-biotin, often bound to proteins or polypeptides.	D-(+)-biotin in its free, crystalline powder form.
Absorption	Bound biotin requires digestive enzymes like biotinidase to be freed for absorption.	Free, synthetic biotin is easily and nonsaturably absorbed by the body.
Delivery	Delivered alongside a host of other nutrients and co-factors in whole foods like egg yolks, legumes, and liver.	A concentrated dose delivered in a supplement format, such as a capsule or tablet.
Common Forms	Biocytin (biotin + lysine) and other biotin-bound peptides.	Free D-(+)-biotin.
Cost	Part of the overall cost of groceries and diet.	A separate, additional expense.

Conclusion: Biotin's Molecular Significance

In summary, biotin is made of a precise arrangement of carbon, hydrogen, nitrogen, oxygen, and sulfur atoms, forming a unique heterocyclic structure with a valeric acid side chain. This specific molecular composition, which is consistent whether found in nature or manufactured synthetically, is what enables its vital function as a coenzyme for carboxylase enzymes. Humans and animals rely on this vitamin from dietary sources, primarily produced by bacteria and plants. The intricate chemistry of biotin is the foundation of its crucial role in cellular metabolism, impacting fatty acid synthesis, amino acid metabolism, and gluconeogenesis. A deeper understanding of its chemical structure provides significant insight into its biological importance and its widespread use in nutritional science. For a more detailed look into the biochemical pathways involving biotin, refer to research articles published by the National Institutes of Health.

Frequently Asked Questions

The primary function of biotin is to act as an essential coenzyme for carboxylase enzymes. These enzymes are involved in critical metabolic processes, including the metabolism of fats, carbohydrates, and amino acids.

The biotin molecule is composed of five elements: carbon (C), hydrogen (H), nitrogen (N), oxygen (O), and sulfur (S), as indicated by its chemical formula, C10H16N2O3S.

No, humans cannot synthesize their own biotin because they lack the necessary enzymes. While intestinal bacteria can produce small amounts, the majority of biotin must be obtained through dietary sources.

The main structural parts of biotin are its fused ring system, which includes a ureido ring and a sulfur-containing tetrahydrothiophene ring, and a valeric acid side chain that extends from the ring structure.

In the biosynthetic process carried out by bacteria and plants, the sulfur atom is inserted into a precursor molecule called dethiobiotin. This final step is catalyzed by the enzyme biotin synthase.

Yes, synthetic biotin, such as that found in supplements, is chemically identical to the D-(+)-biotin found naturally in food. The main difference lies in its delivery format and concentration.

Biotin is a relatively stable vitamin and is not destroyed by typical cooking methods. However, raw egg whites contain a protein called avidin that binds to biotin and prevents its absorption.