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Biochem 2 > Lecture 14 - Nitrogen Metabolism > Flashcards

Lecture 14 - Nitrogen Metabolism Flashcards

1
Q

At what oxidation states does nitrogen exist as in nature?

A

Every form from +5 to -3

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2
Q

What is nitrogen +5?

A

Nitrate (NO3-)

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3
Q

What is nitrogen +4?

A

NO2

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4
Q

What is nitrogen +3?

A

Nitrite (NO2-)

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5
Q

What is nitrogen +2?

A

NO

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6
Q

What is nitrogen +1?

A

N2O2 2-

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7
Q

What is nitrogen 0?

A

Nitrogen gas (N2)

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8
Q

What is nitrogen -1?

A

Di-imide (HN=NH)

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9
Q

What is nitrogen -2?

A

Hydroxyl amine (NH2OH)

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10
Q

What is nitrogen -3?

A

Ammonia (NH3)

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11
Q

What process converts N2 in the air to ammonia?

A

Nitrogen fixation

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12
Q

What process converts ammonia to NO2-?

A

Nitrification

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13
Q

What process converts NO2- to NO3-?

A

Nitrification

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14
Q

What process converts NO3- to N2 in the air?

A

Denitrification

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15
Q

What process converts ammonia to organic nitrogen in living systems?

A

Assimilation

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16
Q

What process converts organic nitrogen in living systems to ammonia?

A

Excretion

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17
Q

What process converts NO3- to ammonia?

A

Nitrate reduction

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18
Q

What is the main source of reduced nitrogen?

A

Nitrogen fixation

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19
Q

What is nitrogen reduction?

A

Conversion of NO3- to NH4+ by plants

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20
Q

What is nitrification?

A

Conversion of NH3 or NH4+ into nitrite and nitrate by bacteria

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21
Q

What nitrification reaction occurs in nitrosomonas?

A

NH3 + O2 -> NO2-

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22
Q

What nitrification reaction occurs in nitrobacter?

A

NO2- + O2 -> NO3-

23
Q

What is the most abundant form of nitrogen in soil?

A

NO3-

24
Q

How much energy is needed to reduce the triple bond of nitrogen gas?

A

930 kJ/mol

25
Q

Nitrogen fixation is carried out by _____

A

Bacteria

26
Q

What 3 types of bacteria carry out nitrogen fixation?

A
  • Azotobacter
  • Clostridium
  • Rhizobium
27
Q

In general, what is nitrogen fixation?

A

A series of three 2 electron transfers that reduce N2 to 2 NH3

28
Q

What are the 2 stages of nitrogen fixation?

A

1) Phosphoroclastic reaction - reduced electron carrier and ATP producing stage
2) Nitrogenase - nitrogen reducing stage

29
Q

Is nitrogen fixation carried out aerobically or anaerobically?

A

Anaerobically

30
Q

How is NO3- converted to NH3?

A
  • NO3- -> NO2- -> N2O2 2- -> NH2OH -> NH3

- Cofactor for each reaction is NADH + H+ -> NAD+

31
Q

What are the 3 main routes for ammonia assimilation that utilize NH3?

A

1) Glutamine synthetase and glutamate synthase
2) Glutamate dehydrogenase
3) Carbamoyl phosphate synthetase

32
Q

High [NH3] can be survived by _____ but not by ______. Why?

A
  • Bacteria; eukaryotes
  • Because the reversal of glutamate dehydrogenase by high [NH3] depletes NADH levels and upsets oxidative metabolism and ATP production
33
Q

What does glutamine synthetase do?

A

Catalyzes the conversion of glutamate to glutamine

34
Q

What are the cofactors needed by glutamine synthetase?

A
  • ATP -> ADP + Pi

- NH3

35
Q

Do all organisms have glutamine synthetase?

A

Yes

36
Q

Which amino acid is in the highest concentration and why?

A
  • Glutamine

- Used as a primary source of NH3

37
Q

In eukaryotes, what is glutamine synthetase the main route for?

A

NH3 assimilation

38
Q

What is the main route for transferring ammonia into amino acids?

A

Glutamate

39
Q

What does glutamate synthase do?

A

Converts glutamine into glutamate, but retains ammonia in the organic form

40
Q

Describe the glutamate synthase reaction

A
  • Alpha-ketoglutarate and glutamine -> glutamate

- Cofactors = NADH + H+ -> NAD+ + H2O

41
Q

Is glutamate synthase found in animals?

A

No, transamination reactions are used instead

42
Q

What does glutamate dehydrogenase do?

A

Converts alpha-ketoglutarate to glutamate

43
Q

What are the cofactors needed for glutamate dehydrogenase?

A

NADH + H+ -> NAD+ + H2O

44
Q

In what organisms does glutamate dehydrogenase work in and why?

A

Bacteria, because they are the only ones that can survive a high enough [NH3] for the enzyme to work

45
Q

To produce NH3, does glutamate work in the forward or backward direction?

A

Backward

46
Q

_____ is a major donor of NH3 in transamination reactions

A

Glutamate

47
Q

Which 2 enzymes produce carbamoyl phosphate?

A
  • Carbamoyl phosphate synthetase (NH3)

- Carbamoyl phosphate synthetase (glutamine)

48
Q

What is the reaction that carbamoyl phosphate synthetase (NH3) catalyzes?

A

NH3 + CO2 + H2O -> carbamoyl phosphate

49
Q

What is the reaction that carbamoyl phosphate synthetase (glutamine) catalyzes?

A

Glutamine + CO2 + H2O -> carbamoyl phosphate

50
Q

What cofactor is needed for carbamoyl phosphate synthetase (NH3)?

A

2 ATP -> 2 ADP + Pi

51
Q

What cofactor is needed for carbamoyl phosphate synthetase (glutamine)?

A

2 ATP -> 2 ADP + Pi

52
Q

Where is the carbamoyl phosphate synthetase (NH3) situated and what is it mainly used for?

A
  • Situated in the mitochondria

- Mainly used for the urea cycle

53
Q

Where is the carbamoyl phosphate synthetase (glutamine) situated and what is it mainly used for?

A
  • Situated in cytoplasm

- Used for pyrimidine synthesis

Biochem 2 (40 decks)

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