Carbon is the central component of all life forms on Earth. It is also the basis of the formation of all naturally occurring organic compounds. 

The capacity of a Carbon atom to form four covalent bonds gives it the ability to form a vast range of compounds. About 40-45% of the total living biomass is Carbon. In the human body, about 12% of all the atoms are Carbon. 


By definition, Organic compounds are those made of a carbon atom covalently linked with Hydrogen or other carbon atoms (forming the backbone). However, a covalent linkage of C--H is a must for a compound to be called organic. 

Britannica defines organic compounds as--

"any of a large class of chemical compounds in which one or more atoms of carbon are covalently linked to atoms of other elements, most commonly hydrogen, oxygen, or nitrogen. The few carbon-containing compounds not classified as organic include carbides, carbonates, and cyanides. "

Among different forms of organic compounds in living organisms- Carbohydrates, Lipids, Proteins and Nucleic Acids are the most important ones. It is because life would not have been possible in this form without them.


These are organic compounds made of Carbon, Hydrogen, and Oxygen. Their general formula is (CH2O)n. Carbohydrates function basically as an energy source and structural component. 

The types of Carbohydrates include:

Simple carbohydrates - Monosaccharides, Disaccharides, and Oligosaccharides (Sugars). Eg. Glucose, Table sugar, Lactose, etc. 

Complex Carbohydrates - Polysaccharides (Starch and Fibres) Eg. Starch, Cellulose, Pectin, etc.


Lipids are a large group of hydrophobic and non-polar (insoluble in water) organic molecules. Lipids include fats, wax, oils, hormones, and other components in living organisms.

Lipids function to store energy (lipids), form structural components (phospholipids), and act as chemical messengers(steroid hormones).

Major types of lipids include:

Phospholipids - Phospholipids are major components of the cell membrane. They are made of fatty acids, phosphoric acid, Nitrogen, and alcohol. 

Triglycerides - Commonly called fats and oils, these are the components we consume in our diets. It constitutes the major volume of lipids (about 95%).

Sterols - Sterols are essential to synthesize and maintain metabolic components. The most important sterol is Cholesterol.


Proteins are highly complex organic molecules found in almost every part of living beings. They are a highly diverse group of molecules in their structure and function. The proteins are formed by the linkage of amino acids by a peptide bond (A bond formed by the Carbonyl group of one molecule with the amino group of another).

Photo by Erol Ahmed on Unsplash

Proteins coordinate and function in almost all the processes of living beings. They carry out different structural (building blocks, cytoskeleton), metabolic (enzymes, hormones, neurotransmitters), protective (immunoglobulins, cell adhesives), and storage. They also have crucial roles in the cell cycle and signaling. 

Based on the function, proteins are of numerous types- 

  • Structural
  • Enzymes
  • Regulatory
  • Transport
  • Sensory
  • Motor
  • Defense
  • Storage and 
  • Signaling proteins.

Nucleic Acids

These are organic biomolecules that store the bits-and-bytes information of living beings such as protein coding and heredity transfer. Nucleic Acids are the primary information-carrying molecules in living beings such as DNA, RNA, etc. Some nucleic acids also function as energy-generating molecules in the cells.

The structure of nucleic acids is a polymerized structure of nucleotides that comprises- a 5-carbon sugar, a nitrogenous base, and a phosphate group. 

 Nucleic acids are primarily of two types. 

Photo by Sangharsh Lohakare on Unsplash

DNA: The structure of DNA is a double-stranded helical structure. Each strand is a polymer of nucleotide units. The nucleotide units in DNA contain - a deoxyribose sugar, a nitrogenous group (Adenine, Guanine, Thymine, or Cytosine), and a phosphate group. 

RNA: RNA is mostly a single-stranded and folded structure. The strand of RNA is a polymer of nucleotide units containing - ribose sugar, a nitrogenous base (Adenine, Guanine, Cytosine, and Uracil), and a phosphate group. 

Read the differences between DNA and RNA.

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