Lecture 14 - Nitrogen Metabolism

Question 1

At what oxidation states does nitrogen exist as in nature?

Answer 1

Every form from +5 to -3

Question 2

What is nitrogen +5?

Answer 2

Nitrate (NO3-)

Question 3

What is nitrogen +4?

Answer 3

NO2

Question 4

What is nitrogen +3?

Answer 4

Nitrite (NO2-)

Question 5

What is nitrogen +2?

Answer 5

NO

Question 6

What is nitrogen +1?

Answer 6

N2O2 2-

Question 7

What is nitrogen 0?

Answer 7

Nitrogen gas (N2)

Question 8

What is nitrogen -1?

Answer 8

Di-imide (HN=NH)

Question 9

What is nitrogen -2?

Answer 9

Hydroxyl amine (NH2OH)

Question 10

What is nitrogen -3?

Answer 10

Ammonia (NH3)

Question 11

What process converts N2 in the air to ammonia?

Answer 11

Nitrogen fixation

Question 12

What process converts ammonia to NO2-?

Answer 12

Nitrification

Question 13

What process converts NO2- to NO3-?

Answer 13

Nitrification

Question 14

What process converts NO3- to N2 in the air?

Answer 14

Denitrification

Question 15

What process converts ammonia to organic nitrogen in living systems?

Answer 15

Assimilation

Question 16

What process converts organic nitrogen in living systems to ammonia?

Answer 16

Excretion

Question 17

What process converts NO3- to ammonia?

Answer 17

Nitrate reduction

Question 18

What is the main source of reduced nitrogen?

Answer 18

Nitrogen fixation

Question 19

What is nitrogen reduction?

Answer 19

Conversion of NO3- to NH4+ by plants

Question 20

What is nitrification?

Answer 20

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

Question 21

What nitrification reaction occurs in nitrosomonas?

Answer 21

NH3 + O2 -> NO2-

Question 22

What nitrification reaction occurs in nitrobacter?

Answer 22

NO2- + O2 -> NO3-

Question 23

What is the most abundant form of nitrogen in soil?

Answer 23

NO3-

Question 24

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

Answer 24

930 kJ/mol

Question 25

Nitrogen fixation is carried out by _____

Answer 25

Bacteria

Question 26

What 3 types of bacteria carry out nitrogen fixation?

Answer 26

- Azotobacter - Clostridium - Rhizobium

Question 27

In general, what is nitrogen fixation?

Answer 27

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

Question 28

What are the 2 stages of nitrogen fixation?

Answer 28

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

Question 29

Is nitrogen fixation carried out aerobically or anaerobically?

Answer 29

Anaerobically

Question 30

How is NO3- converted to NH3?

Answer 30

- NO3- -> NO2- -> N2O2 2- -> NH2OH -> NH3 | - Cofactor for each reaction is NADH + H+ -> NAD+

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

What does glutamine synthetase do?

Answer 33

Catalyzes the conversion of glutamate to glutamine

Question 34

What are the cofactors needed by glutamine synthetase?

Answer 34

- ATP -> ADP + Pi | - NH3

Question 35

Do all organisms have glutamine synthetase?

Answer 35

Yes

Question 36

Which amino acid is in the highest concentration and why?

Answer 36

- Glutamine | - Used as a primary source of NH3

Question 37

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

Answer 37

NH3 assimilation

Question 38

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

Answer 38

Glutamate

Question 39

What does glutamate synthase do?

Answer 39

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

Question 40

Describe the glutamate synthase reaction

Answer 40

- Alpha-ketoglutarate and glutamine -> glutamate | - Cofactors = NADH + H+ -> NAD+ + H2O

Question 41

Is glutamate synthase found in animals?

Answer 41

No, transamination reactions are used instead

Question 42

What does glutamate dehydrogenase do?

Answer 42

Converts alpha-ketoglutarate to glutamate

Question 43

What are the cofactors needed for glutamate dehydrogenase?

Answer 43

NADH + H+ -> NAD+ + H2O

Question 44

In what organisms does glutamate dehydrogenase work in and why?

Answer 44

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

Question 45

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

Answer 45

Backward

Question 46

_____ is a major donor of NH3 in transamination reactions

Answer 46

Glutamate

Question 47

Which 2 enzymes produce carbamoyl phosphate?

Answer 47

- Carbamoyl phosphate synthetase (NH3) | - Carbamoyl phosphate synthetase (glutamine)

Question 48

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

Answer 48

NH3 + CO2 + H2O -> carbamoyl phosphate

Question 49

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

Answer 49

Glutamine + CO2 + H2O -> carbamoyl phosphate

Question 50

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

Answer 50

2 ATP -> 2 ADP + Pi

Question 51

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

Answer 51

2 ATP -> 2 ADP + Pi

Question 52

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

Answer 52

- Situated in the mitochondria | - Mainly used for the urea cycle

Question 53

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

Answer 53

- Situated in cytoplasm | - Used for pyrimidine synthesis