Nitrogen metabolism: fixation and amino acids Flashcards
What is the most common form of nitrogen?
N2 (triple bond - gas)
What converts N2 to a useful form? (4)
Diazotrophs: azo, Brady, photo, Sino - rhizobium
What enzyme do diazotrophs use to fix N2?
Nitrogenase
What is the structure of nitrogenase?
Fe-protein: (homodimer with 2 ATP binding sites)
MoFe-protein: contains Fe and molybdenum
What is nitrogenase inhibited by and how do diazotrophs stop this occurring?
Oxygen
Thick walled cells and no photosystem 2 in root nodules - absence of O2 (must be oxygen freer to work)
What does nitrogen fixation require?
An electron source (oxidatively or photosynthetically)
Why does nitrogen fixation require electrons? (3)
Electrons are transferred to ferrodoxin
Electrons require ATP-dependent protein changes
2 ATP bind to Fe-protein and hydrolyse as an e- passes to MoFe-protein
Where does N2 reduction occur and what is the cost?
N2 reduction occurs on the MoFe protein
e- transfer occurs 6 times per N2 (12 ATP for 1 molecule)
What is the cost of nitrogenase reducing H20 to H2?
8 e- and 16 ATP
What are 3 ways we can obtain fixed N2 without plants?
Lightning discharges
Decaying organic matter
Applied fertiliser
What is the haber-bosch process and what are the conditions?
Industrial N2 creator High temp (200*C) Metal catalyst (iron) High pressure (200atm)
How is nitrogen used once its fixed? (2)
Assimilated into cells biomolecules
Forms amino acids then transaminated (aminotransferase)
Which 2 amino acids are vital for nitrogen use and why?
Glutamate ands glutamine
Act as N donors
What does glutamine synthetase do?
Incorporates an ammonium ion glutamate ti from glutamine
Which amino acids are essential? (10)
Arginine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine
What amino acids are non-essential? (10)
Alanine Asparagine Aspartate Cysteine Glutamate Glutamine Glycine Proline serine Tyrosine
What is the difference between an essential and non-essential amino acid?
Essential: Can’t be synthesised from scratch (diet)
Non - essential: Can be synthesised from intermediates
Where from are essential amino acids synthesised? (3)
Lysine, methionine & threonine: aspartate
Leucine, isoleucine & valine: pyruvate
Phenylalanine, tyrosine & tryptophan: glucose derivatives
How are non-essential amino acids synthesised?
Common metabolic intermediates: pyruvate, oxaloacetate
What are amino acids precursors for? (5)
Nucleotides Nucleotide coenzymes Hormones Heme (globin) Neurotransmitters
How are nucleotides synthesised?
De novo (from scratch) Salvaged
Where are purines and pyrimidines synthesised?
Purines: on the ribose
Pyrimidines: Cytoplasm
What is the one carbon pool?
Single carbons in a variety of oxidation states
What is methotrexate?
Inhibits FH2 to FH4
Used for cancer treatment
