Chapter 24 Flashcards by Dylan Johnson

Used to generate only L - AAs

PLP transaminations

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Source of all AA nitrogen

NH3

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AA C backbone comes from

CAC, glycolysis, pentose phosphate

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net nitrogen fixation rxn

16H20 + 8H+ + N2 + 8e- + 16 ATP&raquo_space; 2NH3 + 16ADP + 16 Pi + H2

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nitrogen fixation enzyme? Two subunits?

nitrogenase complex. Consists of reductase and nitrogenase.

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reductase function

provides e- with reducing power. e- transfer to nitrogenase is coupled to ATP hydrolysis.

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nitrogenase function

reduces N2 to NH3

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nitrogenase complex become inactive by ?

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O2 in root nodules binds to ? to lower O2 concentration to keep nitrogenase complex active

leghemoglobin

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8 high potential electrons for N2 reductiuon come from ?

ferredoxin

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ATP required per electron transfer from reductase to nitrogenase

2 ATP

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importance of ATP hydrolysis in reductase

lowers activation energy to make the rxn KINETICALLY feasible

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reductase and nitrogenase are both this type of protein

Fe-S

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electrons are transferred to this part of the nitrogenase

P-cluster

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ATP binds to this part of reductase

P-loop

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site of nitrogen fixation within nitrogenase

FeMo cofactor

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FeMo cofactor is coordinated to ?

homocitrate

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Acts as N donor for AA’s

glutamate

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Acts as N donor for AA side chains

glutamine

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glutamate dehydrogenase reaction catalyzed

a-KG + NH4+ + NADPH (or NADH) + H+&raquo_space; L-glutamate + H2O + NADP+ (or NAD+)

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glutamine synthase reaction catalyzed

L-glutamate + ATP + NH3&raquo_space; glutamine + ADP + Pi

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glutamate synthase reaction catalyzed

a-KG + glutamine + NADPH&raquo_space; 2glutamate + NADP+

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glutamate synthase function

to synthesize glutamate when NH4+ is scarce. Energetically expensive therefore only highly active at low NH4 concentrations. Low Km for NH4+.

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glutamte dehydrogenase has a low/high Km, therefore it is only affective at low/high NH4+ concentration

high, high

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Alanine is made from ?

pyruvate

serine is made from ? and is used to make ? and ?

3PG. Cysteine and glycine.

glutamate is used to make ? (3)

glutamine, proline, arginine

asparagine is made from ? which is made from ?

aspartate, OAA

histidine is made from ?

R5P

Tyrosine is made from ?

PEP and E4P

? AA's must be consumed in diet

essential

negative nitrogen balance

caused by deficiency in as little as one AA. More protein is degraded than synthesized. More N is excreted than ingested.

complicated AA that is synthesized by humans

Arginine (synthesized in ten steps or in three steps from ornithine of the urea cycle)

PLP transamination dependent AA's formed from alpha-keto acids OAA, pyruvate, and a-KG respectively

aspartate, alanine, glutamate

model aminotransferase

aspartate aminotransferase

conserved sequence among all amontransferaces

lysine residue and arginine residue

function of lysine residue in aminotransferase

forms schiff base with PLP cofactor

function of arginine residue in aminotransferase

interacts w/ a-carboxylate group of the ketoacid

How is only L-AA formed

in the protonation step of the quinonoid intermediate to form an external aldimine, the arginine residue orients the substrate so that the lysine residue adds a proton to the bottom face of the quinonoid substrate.

mechanism for synthesis of asparagine from asparate

aspartate is adenylated by ATP to form acyl-adenylate intermediate and PPi. NH3 (glutamine in mammals) is added to form asparagine and AMP.

Why do mammals use glutamine instead of NH3 in asparagine synthesis?

cell is not exposed to toxic NH4+

intermediates between glutamate and Arginine

glutamic gamma-semialdehyde, ornithine

intermediates between glutamate and Proline

glutamic gamma-semialdehyde, delta-pyrolline 5-carboxylate

intermediates between 3PG and serine

3-phosphohydroxy pyruvate, 3-phosphoserine

reaction catalyzed by serine hydroxymethyltransferase

serine + tetrahydrofolate >> glycine

significance of intermediate in synthesis of proline

nonenzymatic formation of schiff base

Formation of cysteine from serine uses S from ?

methionine/homocysteine

significance of THF

used in glycine synthesis. cannot synthesize in its entirety. must intake as folic acid in our diet. amphibolic. a one-carbon group carrier.

sulfa drugs

antibiotics that inhibit synthesis of THF

THF as an activated one-carbon carrier

group is bonded to its N10 or N5 or both. methyl group in most reduced form. intermediate form carrier methylene. most oxidized form carries formyl, formimo, or methenyl.

fully oxidized one carbon unit ?, is carried by ?

CO2, biotin

activated methyl donor is usually ? because THF transfer potential is too low

SAM

SAM is synthesized by ?

adenylation of methionine with ATP (uses all three Pi)

SAM loses a methyl group to form ?(2)

adenosine and homocysteine

methinine synthase catalyzed formation of methionine from ?. Uses ? as a catalyst.

homocysteine. B12

cysteine is synthesized from ? (2)

homocysteine and serine

two PLP enzymes used in cysteine synthesis

cystathione B-synthase, cystathionase

high homocysteine levels correlate with ?. Caused by mutations in ?.

vascular disease. cystathione b-synthase

betaine-homocysteine methyltransferase reaction catalyzed

betaine + homocysteine >> dimethylglycine + methionine

key intermediates in aromatic AA synthesis

shikimate and chorismate

shikimate is formed from ? (2)

PEP and E4P

chorismate is made from ?

shikimate

glyphosate significance

uncompetitive inhibitor of of chorismate synthesis

chorismate is the precursor for ? (2)

phenylalanine and tyrosine

key substrates in tryptophan synthesis

chorismate, glutamine, PRPP, Serine

tryptophan synthetase structure

a2B2. alpha subunit generates and channels indole. beta uses PLP to activate serine for attachment to indole.

inhibition in serine synthesis

3-PGDH is inhibited allosterically by serine. 4 serines inactivate completely.

a-ketobutyrate is deactivated by high ? conc and activated by ?

isoleucine, valine

3PGDH is structurally similar to ?

threonine deaminase. 4 alpha helices and 8 beta strands.

in E. coli there are three isozymes of ? with different regulatory properties

aspartokinase

glutamine synthase shows ? feedback inhibition from ? (5)

cumulative. Trp, His, carbamoyl-P, CTP, AMP

glutamine synthetase shows ? modification by attachment of ? making it less active

reversible covalent, AMP

adenylation of glutamine synthetase is controlled by ?

uridylylation

interconversion of Pa and Pd. Pa adenylates glutamine synthetase.

organisms capable of nitrogen fixation

bacteria and archaea

transamination swaps ? and ?

carbonyl oxygen and amino group

intermediate in synthesis of phenylalanine, tryptophan, and tyrosine

chorismate

Chapter 24 Flashcards

(77 cards)