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Biol 4890 > Chapter 24 > Flashcards

Chapter 24 Flashcards

1
Q

Used to generate only L - AAs

A

PLP transaminations

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2
Q

Source of all AA nitrogen

A

NH3

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3
Q

AA C backbone comes from

A

CAC, glycolysis, pentose phosphate

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4
Q

net nitrogen fixation rxn

A

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

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5
Q

nitrogen fixation enzyme? Two subunits?

A

nitrogenase complex. Consists of reductase and nitrogenase.

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6
Q

reductase function

A

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

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7
Q

nitrogenase function

A

reduces N2 to NH3

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8
Q

nitrogenase complex become inactive by ?

A

O2

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9
Q

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

A

leghemoglobin

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10
Q

8 high potential electrons for N2 reductiuon come from ?

A

ferredoxin

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11
Q

ATP required per electron transfer from reductase to nitrogenase

A

2 ATP

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12
Q

importance of ATP hydrolysis in reductase

A

lowers activation energy to make the rxn KINETICALLY feasible

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13
Q

reductase and nitrogenase are both this type of protein

A

Fe-S

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14
Q

electrons are transferred to this part of the nitrogenase

A

P-cluster

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15
Q

ATP binds to this part of reductase

A

P-loop

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16
Q

site of nitrogen fixation within nitrogenase

A

FeMo cofactor

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17
Q

FeMo cofactor is coordinated to ?

A

homocitrate

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18
Q

Acts as N donor for AA’s

A

glutamate

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19
Q

Acts as N donor for AA side chains

A

glutamine

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20
Q

glutamate dehydrogenase reaction catalyzed

A

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

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21
Q

glutamine synthase reaction catalyzed

A

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

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22
Q

glutamate synthase reaction catalyzed

A

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

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23
Q

glutamate synthase function

A

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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24
Q

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

A

high, high

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25
Q

Alanine is made from ?

A

pyruvate

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26
Q

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

A

3PG. Cysteine and glycine.

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27
Q

glutamate is used to make ? (3)

A

glutamine, proline, arginine

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28
Q

asparagine is made from ? which is made from ?

A

aspartate, OAA

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29
Q

histidine is made from ?

A

R5P

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30
Q

Tyrosine is made from ?

A

PEP and E4P

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31
Q

? AA’s must be consumed in diet

A

essential

32
Q

negative nitrogen balance

A

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

33
Q

complicated AA that is synthesized by humans

A

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

34
Q

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

A

aspartate, alanine, glutamate

35
Q

model aminotransferase

A

aspartate aminotransferase

36
Q

conserved sequence among all amontransferaces

A

lysine residue and arginine residue

37
Q

function of lysine residue in aminotransferase

A

forms schiff base with PLP cofactor

38
Q

function of arginine residue in aminotransferase

A

interacts w/ a-carboxylate group of the ketoacid

39
Q

How is only L-AA formed

A

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.

40
Q

mechanism for synthesis of asparagine from asparate

A

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

41
Q

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

A

cell is not exposed to toxic NH4+

42
Q

intermediates between glutamate and Arginine

A

glutamic gamma-semialdehyde, ornithine

43
Q

intermediates between glutamate and Proline

A

glutamic gamma-semialdehyde, delta-pyrolline 5-carboxylate

44
Q

intermediates between 3PG and serine

A

3-phosphohydroxy pyruvate, 3-phosphoserine

45
Q

reaction catalyzed by serine hydroxymethyltransferase

A

serine + tetrahydrofolate&raquo_space; glycine

46
Q

significance of intermediate in synthesis of proline

A

nonenzymatic formation of schiff base

47
Q

Formation of cysteine from serine uses S from ?

A

methionine/homocysteine

48
Q

significance of THF

A

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

49
Q

sulfa drugs

A

antibiotics that inhibit synthesis of THF

50
Q

THF as an activated one-carbon carrier

A

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.

51
Q

fully oxidized one carbon unit ?, is carried by ?

A

CO2, biotin

52
Q

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

A

SAM

53
Q

SAM is synthesized by ?

A

adenylation of methionine with ATP (uses all three Pi)

54
Q

SAM loses a methyl group to form ?(2)

A

adenosine and homocysteine

55
Q

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

A

homocysteine. B12

56
Q

cysteine is synthesized from ? (2)

A

homocysteine and serine

57
Q

two PLP enzymes used in cysteine synthesis

A

cystathione B-synthase, cystathionase

58
Q

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

A

vascular disease. cystathione b-synthase

59
Q

betaine-homocysteine methyltransferase reaction catalyzed

A

betaine + homocysteine&raquo_space; dimethylglycine + methionine

60
Q

key intermediates in aromatic AA synthesis

A

shikimate and chorismate

61
Q

shikimate is formed from ? (2)

A

PEP and E4P

62
Q

chorismate is made from ?

A

shikimate

63
Q

glyphosate significance

A

uncompetitive inhibitor of of chorismate synthesis

64
Q

chorismate is the precursor for ? (2)

A

phenylalanine and tyrosine

65
Q

key substrates in tryptophan synthesis

A

chorismate, glutamine, PRPP, Serine

66
Q

tryptophan synthetase structure

A

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

67
Q

inhibition in serine synthesis

A

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

68
Q

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

A

isoleucine, valine

69
Q

3PGDH is structurally similar to ?

A

threonine deaminase. 4 alpha helices and 8 beta strands.

70
Q

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

A

aspartokinase

71
Q

glutamine synthase shows ? feedback inhibition from ? (5)

A

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

72
Q

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

A

reversible covalent, AMP

73
Q

adenylation of glutamine synthetase is controlled by ?

A

uridylylation

74
Q

uridylylation

A

interconversion of Pa and Pd. Pa adenylates glutamine synthetase.

75
Q

organisms capable of nitrogen fixation

A

bacteria and archaea

76
Q

transamination swaps ? and ?

A

carbonyl oxygen and amino group

77
Q

intermediate in synthesis of phenylalanine, tryptophan, and tyrosine

A

chorismate

Biol 4890 (16 decks)

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