Learning outcomes (15-16-17)

Question 1

why is there a discrepancy for nitrogen in the environment but not for use for plants

Answer 1

Nitrogen (N₂) is abundant in the atmosphere but not directly usable by most plants.

Plants require nitrogen in ammonium (NH₄⁺) or nitrate (NO₃⁻) forms.

Question 2

Major Components of the Nitrogen Cycle

Answer 2

Nitrogen Fixation: Conversion of atmospheric N₂ into ammonium by Nitrogen-fixing bacteria like rhizobium

Nitrification: Conversion of ammonium to nitrate by soil bacteria, the more mobile form of nitrogen in the soil

Assimilation: Uptake of ammonium and nitrate by plants (ammonium is directly into AA, but nitrate is reduced to ammonium, then incorporated)

Denitrification: Conversion of nitrate back to N₂ by bacteria.

Question 3

Molecular Nitrogen (N₂):

Ammonium (NH₄⁺):

Nitrate (NO₃⁻):

Nitrite (NO₂⁻):

explain each form

Answer 3

Inert atmospheric form.

Assimilated directly by plants.

Converted to ammonium in plants in AAs

Intermediate in nitrate reduction (nitrite reductase)

Question 4

nitrase reductase

structure, function, and role

Answer 4

Structure:
Contains molybdenum cofactor, dimer or tetramer, heme group and FAD

Function:
Reduces nitrate (NO₃⁻) to nitrite (NO₂⁻).

Role in Nitrogen Assimilation:
First step in converting nitrate to a form usable for amino acid synthesis.

Question 5

Ammonium Assimilation in Plants

Answer 5

Glutamine Synthetase (GS): Converts ammonium and glutamate to glutamine.

Glutamate Synthase (GOGAT): Converts glutamine and 2-oxoglutarate to two molecules of glutamate.

Question 6

Glutamate Dehydrogenase (GDH):
Aspartate Aminotransferase:

Asparagine Synthase:

Answer 6

Reversible conversion of glutamate and ammonium.

Transfers amino groups between glutamate and oxaloacetate

Converts aspartate and glutamine to asparagine.

Question 7

Aminotransferases in Amino Acid Metabolism
role

Answer 7

Facilitate the transfer of amino groups between amino acids and keto acids.

Question 8

Biological Nitrogen Fixation

Answer 8

Conversion of atmospheric N₂ into ammonium by nitrogen-fixing bacteria.

root nodules are structures in legumens that house nitrogen-fixing bacteria (rhizobia).

nitrogenase reduces N2 to NH3 to NH4+

Leghemoglobin: Binds oxygen in root nodules to maintain low oxygen levels, protecting nitrogenase from inactivation.

REQUIRES ATP

Question 9

non biological nitrogen fixation

Answer 9

• haber bosch
• high temperature and pressure
• by natural lightning (falls down with rain)

Question 10

Rhizobia

Answer 10

Free-living nitrogen-fixing bacteria that form symbiotic relationships with legumes.

Question 11

Bacteroids

Answer 11

Differentiated forms of rhizobia within nodules, actively fixing nitrogen.

Question 12

nitrogen compounds in transport

Answer 12

Amides (e.g., asparagine) and ureides (e.g., allantoin):

Used to transport nitrogen within the plant.