Karteikarten
Lecture 29 - Nitrogen cycle and nitrogen fixation
Karten in diesem Stapel (19)
- 1GOALS->Describe the nitrogen cycle
->Understand definitions for nitrogen fixation and nitrogen assimilation
->Describe the reactions catalyzed by nitrogenase, glutamine synthase,
glutamate synthetase, glutamate dehydrogenase, and transaminases /aminotransferases
->Understand definitions of essential and nonessential amino acids - 2TUTORIAL SLIDES Nitrogen Atmospheric nitrogen is non-reactive and must be ___ prior to use. Nitrogen fixation is the ___ of N2 to NH3 (ammonia). This is catalyzed by ___. Ammonia (NH3) is inorganic and must be incorporated into an organic molecule. This is called nitrogen ____. Major mechanism of nitrogen assimilation - Ammonium (NH4+) reacts with glutamate to form ____. Catalyzed by glutamine ____. Glutamate synthase transfers the side chain amino group from glutamine to α-ketoglutarate to generate 2 molecules of _____. Amino groups from amino acids can be transferred to an α keto acid to generate a new amino acid. These ____ reactions are catalyzed by aminotransferases/ transaminases. Animals can make some amino acids (called nonessential amino acids) and must acquire other amino acids from the diet (____ AAs).reduced
reduction
nitrogenase
assimilation
glutamine
synthetase
glutamate
transamination
essential - 3Transamination reactions are catalyzed by ____ or _____ Aminotransferases require the co-enzyme ___aminotransferases or transaminases
PLP - 4—
- 5Nitrogen gas Air is __% N2 N2 is ___ (stable/nonreactive) and we can't use Atmospheric N2 must be ___ to a useful form Nitrogen ____ = reduction of atmospheric N2 - can only be done by some prokaryotes -reaction is very SLOW and requires a lot of ____~78%
inert
reduced
fixation
energy - 6Nitrogen fixation is catalyzed by ______ _____ is a protein complex and reduction occurs in the ___ center. (electrons are transferred from NADH)nitrogenase
nitrogenase
active - 7Nitrogen assimilation Nitrogen assimilation — incorporation of ___ ___ (e.g. NH4+ or N03-) into organic molecules ___ ___ is incorporated into amino acids Organic nitrogen moves through the ecosystem primarily as amino acids ____ ___ — catalyzes this reaction Glutamate + NH4(+) --> Glutamine This reaction is __ dependent To incorporate nitrogen from N03-, the nitrate must be reduced to ____ firstinorganic nitrogen
Inorganic nitrogen
Glutamine synthetase
ATP
ammonium - 8—
- 9Glutamate Synthase •Glutamine acts as nitrogen donor for reductive amination of __-____ Catalyzed by __ ____ (only in prokaryotes and plants) **Requires ____ •Enzyme is NOT present in animals a-ketoglutarate + glutamine + NADPH + H(+) --> 2 glutamate + NADP(+) Amino group from glutamate can be transferred in the synthesis of other moleculesa-ketoglutarate
glutamate synthase
NADPH - 10—
- 11Direct amination of α-ketoglutarate ____ ____ catalyzes this reaction Reaction is REVERSIBLE Reaction primarily runs in reverse in eukaryotes to generate ___ for nitrogen excretion Very MINOR mechanism to ____ nitrogenGlutamate dehydrogenase
NH4+
assimilate - 12Amino Acid Biosynthesis Plants and prokaryotes can make ALL of their amino acids Animals can only make some amino acids (____ amino acids) and must get the other amino acids from their diet (____ amino acids)nonessential
essential - 13Amino Acid Metabolism Principle source of ____ for biosynthetic reactions Source of amino acids is the ___ Metabolic mechanisms are required since dietary amino acids may not be in the proportions that we need Recall gluconeogenesis BCAA (branched-chain amino acids): transport of nitrogen from the ___ to other tissues Amino acids cross cell membranes using specific transport ___nitrogen
diet
liver
proteins - 14Overview of reactions in amino acid and nucleotide biosynthesis Three major types of reactions we will discuss: 1) ____ reactions catalyzed by pyridoxal phosphate-containing enzymes — aminotransferases or transaminases 2) Transfer of one-carbon groups using ___ or ___ cofactors 3) Transfer of amino groups from ____Transamination
THF or SAM
glutamine - 15Transamination reactions ____ reactions Function in synthesis and degradation of amino acids **Aminotransferases — many in eukaryotes: •Cytoplasmic and mitochondrial enzymes •Specifically recognize the donor amino acid and acceptor keto acid •____ is most often DONOR amino acid — α-ketoglutarate/____ pair is important •Oxaloacetate/___pair — important for urea cycle (___ of nitrogen) •Pyruvate/___ pair important in the glucose-alanine cycle (gluconeogenesis)Reversible
Glutamate
glutamate
aspartate
disposal
alanine - 16Mechanism for transamination PLP is covalently bound to ____ ____— PLP now covalently bound to amino acid substrate in active site Hydrolysis of bond leaving the amino group bound to PMP and freeing the __ ___ Reaction then runs in ____ to transfer amino group to a different keto acid to make a new amino acidtransaminase
Transimination
keto acid
reverse - 17—
- 18—
- 19Recap Nitrogen ___- the reduction of atmospheric nitrogen (catalyzed by nitrogenase) Nitrogen ____— the incorporation of ammonia into organic molecules (catalyzed by ____ synthetase) _____— transfer of amino group from amino acid to keto acid to generate new amino acid (catalyzed by transaminases /aminotransferases) Pyridoxal-5'-phosphate (PLP) coenzyme required for ______ Some amino acids are essential (come only from the ___) and some are non-essentialfixation
assimilation
glutamine
Transamination
aminotransferases
diet