Amino Acid Metabolism

Question 1

What is the importance of nitrogen in biochemistry?

Answer 1

Nitrogen (with H, O, and C) is a major elemental constituent of living organisms

Question 2

What is nitrogen mostly in?

Answer 2

Nucleic acids and proteins

Question 3

What is converted in nitrogen fixation?

Answer 3

N2 –> NH3

During nitrogen fixation, molecular nitrogen (N2) serves as substrate for the nitrogenase reaction. Nitrogenase is the primary enzyme involved in nitrogen fixation.

Question 4

Is nitrogen fixation ATP dependent?

Answer 4

Yes, takes 16 ATP to convert N2 –> NH3

Question 5

What is the oxidation state of the nitrogen atom in NO3- (nitrate)?

Answer 5

+5

This is because each oxygen is assigned an oxidation state of –2, and there are three oxygen atoms in nitrate. The overall charge of the polyatomic ion is –1, so the nitrogen atom must be experiencing an oxidation of +5. Compared to other molecules containing nitrogen, +5 is quite oxidized.

Question 6

Symbiotic bacteria synthesize which two amino acids that are used by the plant cell as a source of nitrogen?

Answer 6

glutamate and asparate

Question 7

Does breaking the triple bond of N=N (N2) have very high bond energy?

Answer 7

True

Question 8

What three processes are used to overcome the high energy barrier required to break the nitrogen triple bond?

Answer 8

Biological, Industrial, Atmospheric nitrogen fixation

Question 9

What is biological nitrogen fixation?

Answer 9

Takes place in bacteria

Primary process by which atmospheric N2 gas is converted to ammonium (NH4+) and nitrogen oxides NO2- and NO3-) in the biosphere

Question 10

What is Industrial nitrogen fixation?

Answer 10

Uses N2 and H2 gases under conditions of extreme temperature and pressure to produce NH3

via Haber-Bosch process

Requires Temp ~500C and pressure ~250 atm

Question 11

What is Atmospheric nitrogen fixation?

Answer 11

Occurs when energy from lightning combines N2 with O2 to form nitrogen oxides, which are dissolved in rain and fall to Earth

(lightning breaks the triple bond and combines N with O to form nitrogen oxides that dissolve in rain)

Question 12

How is bacteria useful in fixing nitrogen?

Answer 12

They have the nitrogenase complex that overcomes the high activation energy needed to fix N2 into NH3

Question 13

What are the two functional components of nitrogenase complex?

Answer 13

Reductase (Fe protein)

• provides electrons to nitrogenase
• homodimeric (dimer of two identical subunits)

Nitrogenase (MoFe protein)

• uses electrons to reduce N2 to NH3
• Heterodimeric (tetramer of 2 copies of 2 different subunits)