Question

please somebody answer me by giving diagram that at which step how many atp are formed. it's from biological nitrogen fixation
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Answer 1

Answer:

(d) 16 ATP

Explanation:

NITROGEN FIXATION

· N2 is quite stable (The N≡N has a bond energy of 945 kJ mol−1, versus 351 kJ mol−1 for C−O bond).

· Requires a substantial amount of energy to fix N2 into NH3.

· Can be done by a few strains of bacteria – diazotrophs (such as certain marine cyanobacteria and bacteria that is symbiotic in the roots of legumes).

· Diazotrophs contain “nitrogenase” that catalyzes:

N2 + 8H+ + 8e− + 16 ATP + 16 H2O à 2 NH3 + H2 + 16 ADP + 16 Pi

NITROGENASE

A multi-subunit complex of two proteins (see Fig.20-41)

1. A Fe-protein homodimer g2 containing one [4Fe-4S] cluster and 2 ATP binding sites.

2. A MoFe-protein α2β2 hetero-tetramer containing Mo-Fe cofactor and a P-cluster (consisting of two iron-sulfur clusters).

Mechanism of Nitrogenase

· The required electrons are derived from photosynthesis or oxidative electron transport.

· 2 ATP are utilized for the transfer of one electron.

· 2 ATP bind to reduced Fe-protein and are hydrolyzed as the electron is transferred to MoFe-protein.

· The ATP hydrolysis causes a conformational change of Fe-protein, altering its E°’ from -0.29 to -0.40 V. This enables the subsequent reduction of N2 to 2NH3 (E°’ = -0.34 V for N2 + 6H+ + 6e− ⇌ 2 NH3)

· This occurs in three steps of 2e-reduction:

N≡N + 2H+ + 2e− à H−N=N−H (Diimine)

H−N=N−H + 2H+ + 2e− à H2N−NH2 (Hydrazine)

H2N−NH2 + 2H+ + 2e− à 2 NH3

· The step-wise reduction of N2 occurs on the MoFe-protein.

· However, for every N2 reduced to 2 NH3, at least one additional N2 goes through a 2e-futile cycle via diimine:

N2 + 2H+ + 2e− à HN=NH

HN=NH + H2 à N2 + 2 H2

· Therefore, the overall reaction for the net formation of 2 NH3 from one N2 is:

N2 + 8H+ + 8e− + 16 ATP + 16 H2O à 2 NH3 + H2 + 16 ADP + 16 Pi