21749167
Description
Flashcards by Marissa Alvarez, updated more than 1 year ago
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Created by Marissa Alvarez
almost 5 years ago
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| Question | Answer |
| GOALS | ->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 |
| TUTORIAL 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 |
| Transamination reactions are catalyzed by ____ or _____ Aminotransferases require the co-enzyme ___ | aminotransferases or transaminases PLP |
| Nitrogen 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 |
| Nitrogen fixation is catalyzed by ______ _____ is a protein complex and reduction occurs in the ___ center. (electrons are transferred from NADH) | nitrogenase nitrogenase active |
| Nitrogen 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 ____ first | inorganic nitrogen Inorganic nitrogen Glutamine synthetase ATP ammonium |
| Glutamate 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 molecules | a-ketoglutarate glutamate synthase NADPH |
| Direct 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 ____ nitrogen | Glutamate dehydrogenase NH4+ assimilate |
| Amino 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 |
| Amino 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 |
| Overview 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 |
| Transamination 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 |
| Mechanism 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 acid | transaminase Transimination keto acid reverse |
| Recap 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-essential | fixation assimilation glutamine Transamination aminotransferases diet |
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