Nitrogen Turnover

Why do we need nitrogen in our bodies?

• Nitrogen ranks the fourth most abundant element of the mass of living cells

• amino acids (proteins) have nitrogen

• Nucleic acids (DNA/RNA) have nitrogen

Why do we need nitrogen biomolecules?

• nitrogen brings charge and polarity and allows for complex intra and intermolecular interactions

• peptide bonds in proteins

• hydrogen bonds in nucleic acids in proteins

The origin of N and N cycle in biosphere

• N is abundant but cannot be utilized directly: N2 is very inert

• needs to be converted into ammonia (NH4): nitrogen fixation

  • done by bacteria

• ammonia is further converted to more complex molecules using amino acids as intermediates of N metabolism

Barriers for nitrogen fixation

N2 bond has extremely high energy

• The Haber-Bosch Process: N2 + 3H2 → 2NH3; 200 ATM pressure + 400C

• Nitrogenase complex: lots of ATP required to make 2NH4; normal pressure + RT

  • feeds the entire planet

Two critical amino acids to know

• Glutamate: 5 carbon amino acid, 2 carboxy groups (acidic)

• Glutamine: 5 carbon amino acid, 2 nitrogen groups (amino and amido, net neutral)

main sources of nitrogen

glutamate biochemical reactions

Nitrogen balance (LO1)

• The difference between dietary nitrogen intake and excretion

• it is very difficult to increase/retain nitrogen-containing compounds in the body just by changing nitrogen input

  • nitrogen intake is matched by protein turnover and nitrogen excretion

  • N balance is biochemically orchestrated

• the bulk of nitrogen is in proteins

  • body proteins are predominantly in skeletal muscles

  • can be supplemented from dietary proteins

• body proteins can serve as a major source of energy

Drivers of positive and negative nitrogen balance

• Anabolic (regenerative)

  • testosterone → produced from cholesterol

  • growth hormone

  • insulin

• Catabolic (degenerative)

  • cortisol

  • adrenaline

  • glucagon