Exchange of Carbon & Nitrogen to Build Biological Molecules (College Board AP® Biology)

Carbon & Nitrogen

The Role of Carbon in Organisms

• Carbon is a ubiquitous chemical element in biology

• Carbon dioxide is the ultimate source of the element carbon in all biological systems

• Photosynthesis is the process that removes the carbon from the atmosphere

• Carbon is used to build

  • Carbohydrates

  • Proteins

  • Lipids

  • Nucleic acids

• Carbon is also used to build

  • Storage compounds

    • Such as starch and cellulose

• Carbon can be used in cell formation

  • To build new biological molecules

  • All organisms use processes in new cell formation

The Role of Nitrogen in Organisms

• Nitrogen is also a ubiquitous chemical element in biology

• Nitrogen fixation is the process that removes the nitrogen from the atmosphere

• Nitrogen is used to build

  • Proteins

  • Nucleic acids (DNA and RNA)

  • Urea (an important waste product of protein metabolism that is excreted by animals)

• Nitrogen is a key part in building biomass because of its presence in all amino acids and, therefore, proteins

• Nitrogen exchanges with the environment via the nitrogen cycle

The Role of Phosphorus in Organisms

• Phosphorus is used to build

  • Nucleic acids

  • Some lipids such as phospholipids

Diagram of the Position of Phosphorus in Nucleic Acids and Phospholipids

Phosphate in DNA

Phosphate in phospholipids

Diagram of the key biological molecules required for living organisms

The key biological molecules for living organisms