Biochemistry of Nitrogen Fixation,
Amino Acid Metabolism, and Enzyme
Function Exam Actual Questions and
Answers 2026
2 steps of aa metabolism -
correct answer ✅1. Nitrogen fixation 2. Assimilation
Overcoming large energy barrier for fixation -
correct answer ✅coupled reactions: 1. ATP hydrolysis 2. E-
transfer (redox)
Bacterial enzyme that performs nitrogen fixation -
correct answer ✅nitrogenase complex
Electron donor for nitrogen fixation -
correct answer ✅ferredoxin
Electron acceptor for nitrogen fixation -
correct answer ✅N2 gas
ATP and e- requirement for N fixation -
correct answer ✅16 ATP and 8 e-
,Biochemistry of Nitrogen Fixation,
Amino Acid Metabolism, and Enzyme
Function Exam Actual Questions and
Answers 2026
Why must nitrogen be fixed -
correct answer ✅NH4+ is toxic to cells, must continuously be
regenerated
Structures involved in fixation in nitrogenase complex -
correct answer ✅4Fe:4S cluster → P cluster → FeMo cofactor
Inefficient step of nitrogen fixation -
correct answer ✅2H ⇄ H2 + 2e-
Assimilation involves which two amino acids -
correct answer ✅glutamate and glutamine
Glutamate downstream products -
correct answer ✅aa biosynthesis
Glutamine downstream products -
correct answer ✅carbamoyl-P (see pyrimidine biosynthesis),
glucosamine-6-P, CTP and AMP (nucleotides), tryptophan, histidine
,Biochemistry of Nitrogen Fixation,
Amino Acid Metabolism, and Enzyme
Function Exam Actual Questions and
Answers 2026
Where does primary assimilation of glutamine occur -
correct answer ✅plants
Step 1 of assimilation -
correct answer ✅glutamate → glutamyl-P → glutamine; via
glutamine synthetase
A synthetase requires -
correct answer ✅ATP
Step 2 of assimilation -
correct answer ✅reductive amination of ɑ-ketoglutarate:
glutamine + ɑ-ketoglutarate ⇄ 2 glutamate + ɑ-ketoacid via enzyme
glutamate synthase
A synthase does not require -
correct answer ✅ATP
, Biochemistry of Nitrogen Fixation,
Amino Acid Metabolism, and Enzyme
Function Exam Actual Questions and
Answers 2026
What is an ɑ-ketoacid -
correct answer ✅an amino acid without the NH3 group, ketone
group on alpha C instead
How to regenerate glutamate -
correct answer ✅reductive amination of ɑ-ketoglutarate using
glutamine, a the reverse of every other aa generation
Step 3 of assimilation -
correct answer ✅NH4+ + ɑ-ketoglutarate → glutamate; via
enzyme glutamate dehydrogenase
What is a less efficient way to generate glutamate -
correct answer ✅NH4+ + ɑ-ketoglutarate → glutamate; via
glutamate dehydrogenase
Negative feedback regulation of glutamine -
correct answer ✅excess downstream products of glutamine
inhibit the conversion of glutamate to glutamine
Amino Acid Metabolism, and Enzyme
Function Exam Actual Questions and
Answers 2026
2 steps of aa metabolism -
correct answer ✅1. Nitrogen fixation 2. Assimilation
Overcoming large energy barrier for fixation -
correct answer ✅coupled reactions: 1. ATP hydrolysis 2. E-
transfer (redox)
Bacterial enzyme that performs nitrogen fixation -
correct answer ✅nitrogenase complex
Electron donor for nitrogen fixation -
correct answer ✅ferredoxin
Electron acceptor for nitrogen fixation -
correct answer ✅N2 gas
ATP and e- requirement for N fixation -
correct answer ✅16 ATP and 8 e-
,Biochemistry of Nitrogen Fixation,
Amino Acid Metabolism, and Enzyme
Function Exam Actual Questions and
Answers 2026
Why must nitrogen be fixed -
correct answer ✅NH4+ is toxic to cells, must continuously be
regenerated
Structures involved in fixation in nitrogenase complex -
correct answer ✅4Fe:4S cluster → P cluster → FeMo cofactor
Inefficient step of nitrogen fixation -
correct answer ✅2H ⇄ H2 + 2e-
Assimilation involves which two amino acids -
correct answer ✅glutamate and glutamine
Glutamate downstream products -
correct answer ✅aa biosynthesis
Glutamine downstream products -
correct answer ✅carbamoyl-P (see pyrimidine biosynthesis),
glucosamine-6-P, CTP and AMP (nucleotides), tryptophan, histidine
,Biochemistry of Nitrogen Fixation,
Amino Acid Metabolism, and Enzyme
Function Exam Actual Questions and
Answers 2026
Where does primary assimilation of glutamine occur -
correct answer ✅plants
Step 1 of assimilation -
correct answer ✅glutamate → glutamyl-P → glutamine; via
glutamine synthetase
A synthetase requires -
correct answer ✅ATP
Step 2 of assimilation -
correct answer ✅reductive amination of ɑ-ketoglutarate:
glutamine + ɑ-ketoglutarate ⇄ 2 glutamate + ɑ-ketoacid via enzyme
glutamate synthase
A synthase does not require -
correct answer ✅ATP
, Biochemistry of Nitrogen Fixation,
Amino Acid Metabolism, and Enzyme
Function Exam Actual Questions and
Answers 2026
What is an ɑ-ketoacid -
correct answer ✅an amino acid without the NH3 group, ketone
group on alpha C instead
How to regenerate glutamate -
correct answer ✅reductive amination of ɑ-ketoglutarate using
glutamine, a the reverse of every other aa generation
Step 3 of assimilation -
correct answer ✅NH4+ + ɑ-ketoglutarate → glutamate; via
enzyme glutamate dehydrogenase
What is a less efficient way to generate glutamate -
correct answer ✅NH4+ + ɑ-ketoglutarate → glutamate; via
glutamate dehydrogenase
Negative feedback regulation of glutamine -
correct answer ✅excess downstream products of glutamine
inhibit the conversion of glutamate to glutamine
