Organic Molecules: Structure, Function, and Examples

Organic Molecules

Organic molecules are the chemical compounds that form the basis of life. The four major classes—carbohydrates, lipids, proteins, and nucleic acids—each have unique structures and functions essential to living organisms.

Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio. They serve as a primary energy source and provide structural support in plants.

• Function(s): Energy source and structural support in plants

• Chemical Makeup: Carbon, hydrogen, oxygen; 1:2:1 ratio

• Monomer(s): Monosaccharide (simple sugars such as glucose)

• Examples: Glucose, sucrose, starch, cellulose, glycogen

• Additional Information:

  • Names often end in -ose (e.g., glucose, sucrose)

  • Starch: storage form of sugar in plants

  • Cellulose: provides structural support in plant cell walls

  • Glycogen: storage form of sugar in animals

  • Pentose: Monosaccharide with 5 carbon atoms

  • Aldose: Monosaccharide containing an aldehyde group

Lipids

Lipids are hydrophobic molecules made mostly of carbon and hydrogen, with little oxygen. They are important for cell membrane structure, energy storage, and insulation.

• Function(s): Make up cell membranes; structural support; communication; long-term energy storage

• Chemical Makeup: Carbon, hydrogen, oxygen; lots of C and H, little O

• Monomer(s): Fatty acid tail

• Examples: Triglycerides, phospholipids, sterols

• Additional Information:

  • Fatty acid tails can be saturated (solid, single bonds) or unsaturated (liquid, double bonds)

  • Phospholipids are key components of cell membranes

Proteins

Proteins are polymers made of amino acids. They perform a wide range of functions, including catalyzing reactions, structural support, transport, and immune defense.

• Function(s): Enzymatic activity, communication, structure, transport, immunity, defense

• Chemical Makeup: Amine and carboxyl groups around a central carbon

• Monomer(s): Amino acid

• Examples: Enzymes, hemoglobin, antibodies

• Additional Information:

  • Primary structure: linear sequence of amino acids

  • Secondary structure: alpha helix or beta-pleated sheet

  • Tertiary structure: folding based on R group interactions

  • Quaternary structure: multiple polypeptide chains joined together

  • Form peptide bonds between amino acids

Nucleic Acids

Nucleic acids store and transmit genetic information. They are polymers made of nucleotide monomers.

• Function(s): Heredity, protein synthesis, energy transfer

• Chemical Makeup: 5-carbon sugar (pentose), phosphate group, nitrogenous base

• Monomer(s): Nucleotide

• Examples: DNA, RNA

• Additional Information:

  • DNA contains deoxyribose sugar; RNA contains ribose sugar

  • DNA stores genetic information; RNA is involved in protein synthesis

  • Nucleotides are composed of a sugar, phosphate group, and nitrogenous base

Comparison Table: Major Organic Molecules

Category	Carbohydrates	Lipids	Proteins	Nucleic Acids
Function(s)	Energy source, structural support in plants	Cell membrane structure, energy storage, insulation	Enzymatic activity, structure, transport, immunity	Genetic information storage, protein synthesis
Chemical Makeup	C, H, O (1:2:1)	C, H, little O	Amine and carboxyl groups, central carbon	Pentose sugar, phosphate, nitrogenous base
Monomer(s)	Monosaccharide	Fatty acid tail	Amino acid	Nucleotide
Examples	Glucose, sucrose, starch, cellulose, glycogen	Triglycerides, phospholipids, sterols	Enzymes, hemoglobin, antibodies	DNA, RNA
Additional Info	Names end in -ose; storage and structural roles	Saturated/unsaturated; hydrophobic	Primary to quaternary structure; peptide bonds	DNA: deoxyribose; RNA: ribose