BIOL301 Class 15 Flashcards
How can nitrogen enter the Biosphere?
- N2 Fixation
- N2 Assimilation
N2 is extremely abundant but the cost and difficulty of nitrogen fixation has made nitrogen assimilation the predominant strategy
nitrogen cycle
- environmental sources of N are mostly in oxidized forms (N2, NO2-, NO3-)
- movement of N into the biosphere requires reduction of N2 into usable forms
- plants and bacteria can readily reduce Nitrate to Ammonia (assimilation)
- animals must acquire Nitrogen from Diet
nitrogen fixation
- found only in prokaryotes but this is the only biologival tap into the largest reservoir of N in the world: atmospheric N2
- although the reaction is exothermic overall (favorable) the strong bonding of the 2 N atoms creates a huge energy of activation that is impossible
- industrial fixation of nitrogen requires heating nitrogen and hydrogen gasses to 500 deg C under 300 atm pressure!
- picture **
nitrogen fixation is catalyzed by the nitrogenase complex
- bacteria do this
picture - essentially an electron transport chain that reduces N2 to NH4+
nitrogen assimilation
- accounts for 99% of all nitrogen acquisition into the biosphere
- Nitrate reductase
- Nitrite reductase
- the goal is to get nitrogen into a reduced state that can be directly incorporated into biomolecules (ammonia)
picture - ammonium can be then brought into metabolism via multiple mechanisms that lead to either glutamate or glutamine
1) glutamate dehydrogenase
- uses the reductive power of NAD(P)H to drive amination of alpha ketoglutarate
- links nitrogen metabolism to carbon and energy metabolism
- found in bacteria and plants; in mitochondria of mammals
picture
how does glutamate dehydrogenase link nitrogen metabolism to carbon and energy metabolism ?
glutamate dehydrogenase links nitrogen metabolism to carbon and energy metabolism by converting glutamate to α-ketoglutarate. This process facilitates the incorporation of nitrogen-containing molecules into the citric acid cycle for energy production while simultaneously detoxifying ammonia.
In which direction would increased NADP+/NADPH drive the reaction? increased glu? under what conditions might you want to change the direction?
- an increased NADP⁺/NADPH ratio would favor the reduction of α-ketoglutarate to glutamate
- higher concentrations of glutamate would favor the forward reaction of GDH, leading to the production of α-ketoglutarate.
- If the cell requires ATP or NADH, it may want to favor the oxidative deamination reaction of GDH, which converts glutamate to α-ketoglutarate, producing NADH and NH₄⁺. This reaction occurs under conditions of high energy demand, such as during intense exercise or periods of fasting.
2) Glutamine Synthetase (GS)
- catalyzes ATP-dependent amidation of glutamate to yield glutamine
- present in ALL organism
- glutamine can donate nitrogen to alpha ketoacids to generate other amino acids and is also important for nucleic acid biosynthesis
- in plants and bacteria, its used in low NH4+ environments
in mammals GS is used to remove toxic NH$+ from amino acid catabolism (synthesis)
picture
Regulation of E.coli glutamine synthetase
- E. coli glutamine synthetase plays a vital role in nitrogen assimilation and metabolism, contributing to the synthesis of glutamine, an essential molecule in numerous cellular processes.
- Glutamine synthetase is often regulated by feedback inhibition and post-translational modification to ensure proper control of glutamine synthesis in response to cellular nitrogen and energy status
picture
3) Glutamate Synthase (GOGAT)
- prokaryotes & plants
- reductive transfer of NH3 from one molecule of Gln to alpa-KG to yield 2 molecules of glutamate
- used in combination with glutamine synthetase for additional glutamate synthesis
- glutamate can be used for protein synthesis & ammonia detoxification
two pathways available for nitrogen assimilation through glutamate
1) GDH Pathway
2) GS-GOGAT Pathway
Picture
amino acid biosynthesis
- once nitrogen is organically integrated, all amino acids can theoretically be built by:
1) assembling the carbon skeletons (alpha keto acid followed. by
2) transamination reactions: transferring amino group from an abundant amino acid (glutamate) to the alpha keto acid of a new amino acid
what do transaminase enzymes do
catalyze the reversible transfer of an amino group between two alpha keto acids
what symptoms/defects might vitamin B6 deficiency create?
Vitamin B6 deficiency can cause various problems:
Numbness or tingling in hands and feet.
Skin issues like rashes and cracked lips.
Anemia and weakened immune system.
Mood changes like depression and irritability.
Increased risk of heart disease.
Hormonal imbalances and menstrual irregularities.
