Nitrogen Flashcards
Describe the first stage of converting atmospheric nitrogen to dietary protein.
Nitrogen fixation: Certain bacteria (e.g., Rhizobium, found in legume root nodules) convert atmospheric nitrogen (N₂) into ammonia (NH₃) through nitrogenase enzymes.
Describe the stage after nitrogen fixation.
Nitrification: Ammonia in the soil is converted by soil bacteria into nitrite (NO₂⁻) and then to nitrate (NO₃⁻), which plants can absorb.
Describe the stage after nitrification.
Plants assimilate nitrate or ammonia into organic molecules, forming amino acids like glutamate and glutamine, which serve as nitrogen donors for other amino acids.
How is alanine derived?
Pyruvate; direct product of glycolysis.
What is the biosynthetic precursor of serine and where does it come from?
3-phosphoglycerate, a glycolysis intermediate.
How is glutamate synthesised?
From α-ketoglutarate, an intermediate in the citric acid cycle, through a transamination reaction.
How is aspartate formed?
From oxaloacetate through a transamination reaction.
What are biogenic amino acids?
Those that play active roles in metabolism, acting as precursors to various biomolecules essential to life.
List functions biogenic amino acids are fundamental in.
Neurotransmission, hormone synthesis, detoxification and immune response.
What are the two categories of amino acids?
Glucogenic and ketogenic (or both)
Define glucogenic amino acids and name two examples.
Degrade into intermediates that can enter gluconeogenesis - alanine, cysteine, serine, aspartate and methionine.
Define ketogenic amino acids and name two examples.
Degrade into acetyl-CoA or acetoacetate, which can lead to ketone body production - leucine and lysine.
How do terrestrial animals excrete nitrogenous waste?
Mainly as urea through the urea cycle.
How do birds and reptiles excrete nitrogen?
Excrete nitrogen in the form of uric acid.
How do fish excrete nitrogen?
Generally excrete ammonia directly into the water through gills.
