Nitrogen Metabolism

Sources of atoms in amino acids/nucleotides

Inorganic C&N, organic C&N, building blocks, macromolecules

Atmospheric nitrogen

Animals/plants, ammonium, nitrites, nitrates, atmosphere N2, nitrogen bacteria

Inorganic nitrogen/precursor to organic nitrogen

ammonia

Organic form of Nitrogen

glutamate, glutamine, carbamoyl phosphate

Reservoir of inorganic nitrogen

Nitrate and nitrites in soil, N2 in atmosphere

Cells excrete nitrogen as:

urea/ammonia

Nitrogen fixation

bacteria process (high energy), 2 ATP hydrolyzed e- transferred

Fixation Reaction

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

Nitrate/Nitrite Reduction

nitrate to nitrite, nitrite to ammonia

Nitrate reducing enzyme

Nitrate reductase, NADH or NADPH as reductant

Nitrite reducing enzyme

Nitrite reductase, catalyzes 3 reductions, NO2 -> NO -> NHOH -> NH3

Glutamate Enzyme

Glutamate dehydrogenase

Glutamate Synthesis Driver

NADPH

Which Stereoisomer of glutamate is synthesized

L-Glutamate

CAC intermediate needed for Glutamate

alpha-ketoglutarate

Enzyme for Glutamine Synthesis

Glutamine Synthetase

Glutamine Driver

Cleavage of ATP equivalent

What can Glutamine donate to other compounds

amide nitrogen from end of side chain

What is the most abundant reservoir of inorganic nitrogen on Earth?

Molecular nitrogen (N₂)

What is nitrogen fixation?

The conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) by specialized nitrogen-fixing bacteria, requiring ATP and reducing equivalents.

Which enzyme catalyzes the synthesis of glutamine

Glutamine synthetase

What is the immediate precursor of organic nitrogen forms?

Ammonia (NH₃)

Which organic molecules are the first to receive nitrogen in metabolism?

Glutamate, glutamine, and carbamoyl phosphate

What are the two major types of nitrogen reduction processes?

Nitrate reduction and nitrite reduction

What is the primary function of the urea cycle?

To remove excess nitrogen by converting it into urea for excretion

Which enzyme catalyzes the synthesis of glutamate?

Glutamate dehydrogenase

What is the role of transamination reactions?

Transfer of amino groups between amino acids and keto acids, primarily using glutamate as the donor.

What is the primary nitrogen donor in amino acid biosynthesis?

Glutamate

What is the coenzyme involved in transamination reactions?

Pyridoxal phosphate (PLP), derived from vitamin B6

What is the primary site for amino acid metabolism in the body?

The liver

What is the major excretory form of nitrogen in mammals?

Urea

What is the difference between glucogenic and ketogenic amino acids?

Glucogenic amino acids are converted into glucose precursors, while ketogenic amino acids are converted into ketone bodies.

Which amino acids are exclusively ketogenic?

Leucine and lysine

What is the key intermediate in the urea cycle that donates nitrogen?

Carbamoyl phosphate

How is nitrogen transported between tissues?

Primarily via glutamine and alanine, which carry excess nitrogen to the liver for excretion.

What is the significance of tetrahydrofolate (THF) in metabolism?

It serves as a carrier for one-carbon groups in nucleotide and amino acid synthesis.

What is the first step in the breakdown of phenylalanine?

Conversion to tyrosine by phenylalanine hydroxylase

What causes phenylketonuria (PKU)?

A deficiency in phenylalanine hydroxylase, leading to accumulation of phenylalanine and neurological damage.

How do aquatic organisms excrete nitrogen?

As ammonia (NH₃), directly into the surrounding water.

How do birds and reptiles excrete nitrogen?

As uric acid, which requires minimal water for excretion.

How do mammals excrete nitrogen?

As urea, which is less toxic and can be concentrated in urine.

What is the function of carbamoyl phosphate synthetase?

It catalyzes the first step in the urea cycle by synthesizing carbamoyl phosphate from NH₃ and CO₂.

Which vitamin-derived molecule is essential for transaminase reactions?

Pyridoxal phosphate (PLP), from vitamin B6.

What is the main function of the Cori cycle?

It recycles lactate from muscles back to glucose in the liver.

What is the fate of excess amino acids in the body?

They are deaminated, and their carbon skeletons are used for energy or stored as fat.

How is nitrogen balance maintained in the body?

By balancing nitrogen intake (dietary protein) with nitrogen excretion (urea, ammonia, uric acid).

What are essential amino acids?

Amino acids that cannot be synthesized by the human body and must be obtained from the diet.