Lecture 14 - Nitrogen Fixation Mechanism

Question 1

Step 1

Answer 1

Pyruvate -> acetyl-CoA

Question 2

Enzyme of step 1

Answer 2

Pyruvate dehydrogenase

Question 3

Cofactor of step 1

Answer 3

• CoA-SH -> CO2

- NAD+ -> NADH + H+

Question 4

Step 2

Answer 4

Acetyl-CoA -> acetyl-phosphate

Question 5

Enzyme of step 2

Answer 5

Phospho transacetylase

Question 6

Cofactor of step 2

Answer 6

Pi -> CoA-SH

Question 7

Step 3

Answer 7

Acetyl-phosphate -> acetate

Question 8

Enzyme of step 3

Answer 8

Acetate kinase

Question 9

Cofactor of step 3

Answer 9

ADP -> ATP

Question 10

What 2 proteins make up the nitrogenase complex?

Answer 10

• Dinitrogenase reductase (azoferridoxin)

- Dinitrogenase (molybdoferridoxin)

Question 11

How many electrons does nitrogenase require?

Answer 11

8 (6 for NH3, and 2 for H2)

Question 12

What is always produced as a biproduct of nitrogen fixation?

Answer 12

H2

Question 13

What happens to the ammonia produced by nitrogen fixation?

Answer 13

It can be incorporated directly into organic form, or excess is excreted into soil where it is converted into nitrate by bacteria

Question 14

What happens to the energy produced by nitrogen fixation?

Answer 14

It is used by Nitrosomonas and Nitrobacter for growth

Question 15

Can NO3- be used or must it be converted to something else?

Answer 15

Must be reduced to ammonia to be used

Question 16

What do plants use nitrates for?

Answer 16

Incorporation of nitrogen into amino acids

Question 17

What reaction occurs in the dinitrogenase reductase protein of the nitrogenase complex?

Answer 17

Fe-prot (reduced) -> Fe-prot (reduced) + 16 ATP -> Fe-prot (oxidized) + 16 ADP + Pi -> Fe-prot (oxidized) -> Fe-prot (reduced)

Question 18

What cofactor is needed to convert Fe-prot (reduced) to Fe-prot (reduced) + 16 ATP?

Answer 18

16 ATP in

Question 19

What cofactor is needed to convert Fe-prot (reduced) + 16 ATP to Fe-prot (oxidized) + 16 ATP + 16 Pi?

Answer 19

8 electrons

Question 20

What cofactor is needed to convert Fe-prot (oxidized) + 16 ADP + 16 Pi to Fe-prot (oxidized)?

Answer 20

16 ADP + 16 Pi out

Question 21

What reaction is coupled to the conversion of Fe-prot (oxidized) to Fe-prot (reduced)?

Answer 21

Ferridoxin (reduced) -> ferridoxin (oxidized)

Question 22

What reaction is coupled to the conversion of ferridoxin (oxidized) to ferridoxin (reduced)?

Answer 22

NADH + H+ -> NAD+ + 2H+

Question 23

What reaction is coupled to the conversion of Fe-prot (reduced) + 16 ATP to Fe-prot (oxidized) + 16 ADP + 16 Pi?

Answer 23

MoFe-prot (oxidized) + N triple-bond N -> MoFe-prot (reduced) + N triple-bond N

Question 24

What reaction occurs in the dinitrogenase protein of the nitrogenase complex?

Answer 24

MoFe-prot (oxidized) + N triple-bond N -> MoFe-prot (reduced) + N triple-bond N-> MoFe-prot (oxidized) + HN=NH -> MoFe-prot (oxidized)

Question 25

What cofactor is needed to convert MoFe-prot (reduced) to MoFe-prot (oxidized) + HN=NH?

Answer 25

2 H+ in

Question 26

What happens to MoFe-prot (oxidized) + HN=NH?

Answer 26

Converted to N2H4, and then NH3

Question 27

What cofactor is needed to convert MoFe-prot (oxidized) to MoFe-prot (oxidized) + N triple-bond N?

Answer 27

N2 in