The human body is composed of cells that are fundamentally made up of several different molecules. These molecules are essential to carry out all physiological processes in the body and are broadly classified into organic and inorganic based on their chemical structures.

Inorganic Compounds Essential to Human Functioning

Inorganic compounds essential to human functioning include water, salts, acids, and bases. These compounds are inorganic, i.e., they do not have a carbon-hydrogen bond. Water is a lubricant, a cushion, a heat sink, a component of liquid mixtures, a by-product of dehydration synthesis reactions, and a reactant in hydrolysis reactions. Salts are an important group of compounds and a source of several minerals. When dissolved in water, salts dissociate into ions other than H⁺ or OH^–. In contrast, acids release H⁺ in the solution upon dissociation. Bases accept H⁺, thereby making the solution more alkaline. Salts, acids, and bases, collectively termed electrolytes, are essential for homeostatic control mechanisms of body fluids.

Organic Compounds Essential to Human Functioning

Organic compounds, including carbohydrates, lipids, proteins, and nucleotides, are also vital for the body. These compounds are defined as organic because they contain carbon and hydrogen. Carbohydrates are a unique group of compounds that act as fuel to generate energy for the body. They include monosaccharides such as glucose; disaccharides such as lactose; and polysaccharides, including starches (polymers of glucose), glycogen (the storage form of glucose), and indigestible dietary fibers.

Lipids are hydrophobic compounds that act as a source of reserve energy and are also essential components of many cell organelles, such as cell membranes. Phospholipids are amphipathic, meaning they contain both hydrophobic and hydrophilic groups. In the cell membrane, their hydrophilic phosphate heads face the water present outside and inside the cell, whereas the hydrophobic tails face each other to form a bilayer. Triglycerides are the most abundant lipid in the body, composed of a glycerol backbone attached to three fatty acid chains. Some lipid derivatives, like prostaglandins, act as signaling molecules.

Proteins are critical components of all body tissues. They are composed of amino acid monomers joined by peptide bonds to form long polypeptide chains. These polypeptide chains fold to form a secondary and tertiary structure.

The nucleic acids, DNA and RNA, are polymers of nucleotides. These nucleotides are primarily composed of three primary building blocks— a phosphate group, a pentose sugar, and a nitrogenous base. DNA stores genetic information. This information is transferred to the RNA. The RNA acts as a blueprint for protein synthesis essential to the survival and reproduction of an organism.

Adenosine triphosphate (ATP) is composed of a ribose sugar, an adenine base, and three phosphate groups. It is classified as a high-energy compound because the two covalent bonds linking to three phosphates store a significant amount of potential energy. The energy released from these high-energy bonds in the body helps fuel the body's activities, such as muscle contraction, nutrient transport, and metabolic reactions.

This text is adapted from Openstax, Anatomy and Physiology 2e, Section 2.4: Inorganic Compounds Essential to Human Functioning; Openstax, Anatomy and Physiology 2e, Section 2.5: Organic Compounds Essential to Human Functioning.