GOALS

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).

Transamination reactions are catalyzed by ____ or _____

Aminotransferases require the co-enzyme ___

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 ____

Nitrogen fixation is catalyzed by ______

_____ is a protein complex and reduction occurs in the ___ center.

(electrons are transferred from NADH)

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

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

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

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)

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 ___

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 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)

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

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