nitrogen Flashcards
N2 cycle
process (biological + physical) by which N2 converted bet various chem forms
1. fixation
2. ammonification
3. nitrification
4. denitrification
symbiotic nitrogen fixation
N2 in air -> NH3/NH4+ for use by plants
* carried out by nitrogenase complex (dinitrogenase reductase + dinitrogenase)
* plant has mutualistic relationship w nitrogen-fixing bac, e.g. Rhizobium = can survive independently but benefit each other - provide NH3 + carbs respectively
in plants harbouring N2-fixing bac w/in tissues = DONE IN PLANTS
major storage form N in soil
NO3-
conversion soil nitrate + nitrite to ammonia
w equs
reduction NO3- + NO2- to NH3 in bac in soil/in plants as required for building blocks make aas
how is NH3 present in plants
usually as NH4+ at physiological pH (7.4)
incorporation NH3 into aas
- NH3 -> glutamate using glutamate dehydrogenase
- glutamate -> glutamine using glutamine synthase
which aas synthed from glutamate
- glutamine
- proline
- arginine - missing final part synth pathway in mammals = can’t make, have to eat
transamination
transfer of amino grp (-NH2) bet aas - usually from glutamate
role of precursor in citric acid cycle for biosynth aas
oxaloacetate precursor aspartate, which is a precursor for other aas, all part aspartate family
of these, only asparagine has biosynthetic pathway for synth in animals
how is asparagine synthed from aspartate
transfer amine grp from glutamine to aspartate by asparagine synthase
biosynth precursor serine family aas
3-phosphoglycerate
aas for which pyruvate precursor
alanine, valine, leucine
* only alanine has biosynthetic pathway in mammals
essential vs non-essential aas defn
aas that must be provided in diet to meet animal’s metabolic needs
non-essential = no need provide as can be biosynthed in adequate amounts
some non-essential become essential in growth/illness - need start eating it as can’t make
list essential aas
- arginine
- histidine
- isoleucine
- leucine
- lysine
- methionine
- phenylalanine
- threonine
- tryptophan
- valine
use tryptophan
precursor for serotonin (NT) - marketed sleep aid + antidepressant
use leucine
additive flavour enhancer - slows degradation muscle by increasing muscle prot in ageing rats
use methionine
racemic mix added pet foods
biogenic amines - how formed, examples w precursor + function
table
formed decarboxylation aas
pathway for catecholamine biosynth
glucogenic vs ketogenic aas
try to give degradation products
glucogenic broken down to citric acid cycle intermediates
* can be converted to glucose by gluconeogenesis
ketogenic broken down to acetyl-CoA or acetoacetate
* can be converted to ketone bodies (= emergency fuel source)
some aas are both
how are aas broken down for excretion mammals
- Transamination: aa gives amine grp to α-ketoglutarate = glutamate, cated aminotransferase/transaminase
- Deamination: glutamate broken down to α-ketoglutarate by glutamate dehydrogenase, releasing NH4+
- NH4+ used make urea
- urea is safe for excretion
how is NH3 excreted
free NH3 excreted by conversion to urea in urea cycle in liver as free NH4+ toxic bc reacts w lots things
How is nitrogen in NH4+ transported to liver
for conversion to urea
ammonium ions converted to alanine or glutamine for transport in blood
* alanine then converted to glutamate + deaminated in liver
how is urea excreted
- in mammals by the kidneys + in saliva + sweat
- in ruminants into GI sys where can be reused for aa biosynth
N2 excretion in aquatic animals
directly excrete ammonium = ammonotelic
* NH4+ gened in gills by deamination, secreted + rapidly diluted in aquatic environ
sharks + cartilaginous fish can prod urea asw as NH3
nitrogen excretion in birds + reptiles
excrete N2 as uric acid = ureotelic
* conserves water even though uses relatively large amount E
uric acid formed following generation aspartate, glutamine, glycine, then synth purine nucleotides - degradation purine prods uric acid
also occurs in mammals + fish but not primary route N2 excretion
ruminant nitrogen metabolism
- prots hydrolysed to aas by ruminal microbes
- prots that escape digested in SI where aas absorbed
- ruminal microbes use aas for own prot synth or degrade them further to ammonia
- some ammonia to liver for conversion to urea + excretion
- rumen microbes fix ammonia into aas - can make any want, used make microbial prots
- microbial prots digested + absorbed in SI
can reabsorb urea, used make aas + incorporated prots
