BB451 Nitrogen Metabolism

What chemical denotes atmospheric nitrogen?

N2

Which organisms can convert nitrogen into a usable form?

Bacteria can (through nitrogen fixation), most plants and animals cannot.

Can you name some cellular molecules made with nitrogen?

Amino acids and nucleotides.

Can we use atmospheric nitrogen to make amino acids?

No.

What is the nitrogen cycle?

The series of processes by which nitrogen and its compounds are interconverted in the environment and in living organisms, including nitrogen fixation and decomposition.

What is transamination?

The transfer of an amino group from one molecule to another.

Name some non-protein amino acids.

Ornithine, Citrulline, Sacrosine.

How is nitrogen excreted by fish?

Ammonia.

How is nitrogen excreted by birds?

Uric acid.

How is nitrogen excreted by most vertebrates?

Urea.

Why do you check the pH of your fish tank frequently?

Ammonia levels can build up.

How do humans excrete excess nitrogen?

Urea (primary), but also uric acid.

How is the glucose-alanine cycle like the Cori Cycle?

Both cycles involve the transport of a metabolic byproduct from muscle tissue to the liver for conversion back into glucose, with the glucose-alanine cycle converting pyruvate to alanine.

How is glutamate important in nitrogen metabolism?

It acts as a primary acceptor of amino groups, serving as a key hub for transferring nitrogen within the body.

What is the urea cycle? Where does it occur?

It occurs in the liver and kidney, consisting of 4 cycle reactions and 1 feeder reaction.

What happens when free ammonium ions are picked up?

They are combined with bicarbonate to make carbamoyl phosphate.

What is made next after carbamoyl phosphate?

Citrulline.

What can happen to citrulline after it is formed?

It can be transported out of the mitochondria and react with aspartic acid.

What does the enzyme arginase do?

Cleaves arginine to make urea and ornithine.

What is the mnemonic for the urea cycle?

Orange Colored Cats Always Ask For Awesome Umbrellas.

What else do cells use citrulline for?

It produces nitric oxide, used for cell signaling (vasodilation).

What are two ways citrulline is made?

1. As a byproduct of the urea cycle, 2. By the breakdown of arginine.

What amino acids are in the glutamate family?

Glutamate, arginine, glutamine, proline.

What do the glutamate family amino acids derive from?

Alpha-ketoglutarate.

Why is the synthesis of glutamate family amino acids carefully regulated?

They are starting materials for many other amino acids.

What amino acids are in the serine family?

Serine, cysteine, glycine, selenocystine.

What do serine family amino acids derive from?

3-phosphoglycerate.

How does cysteine obtain its sulfhydryl group?

From methionine.

How does serine convert to glycine?

By removal of the CH2OH group.

What else is needed for serine to become glycine?

Folate with CH2OH can provide it back.

What is special about selenocysteine?

It contains selenium and is encoded by a stop codon.

What enzyme uses selenocysteine?

Thioredoxin reductase.

What amino acids are in the aspartate family?

Aspartate, asparagine, lysine, threonine, methionine.

What amino acids are in the aromatic family?

Tryptophan, phenylalanine, tyrosine.

What relevant molecules are made from the aromatic family?

Melatonin, serotonin, thyroid hormones, melanin.

What does tryptophan give rise to?

Melatonin, serotonin, Niacin (B3), Auxins.

What sugar replacement is made with phenylalanine?

Nutrasweet (aspartame).

What is the disease PKU?

Deficiency of the phenylalanine hydroxylase enzyme.

What molecules are made from tyrosine?

Catecholamines: Dopamine, epinephrine/norepinephrine.

How is tyrosine relevant to Parkinson’s Disease?

There are problems with dopamine synthesis; treated with L-Dopa.

Where do thyroid hormones derive from?

Tyrosine, containing iodine.

How is tyrosine related to melanin?

Melanin is oxidized and polymerized tyrosine.

What amino acids are in the pyruvate family?

Alanine, leucine, isoleucine, valine.

Which amino acids are branched-chain?

Valine, leucine, isoleucine.

What is maple syrup urine disease?

Inability to metabolize branched-chain amino acids.

What amino acid is in the histidine family?

Histidine.

What is notable about how histidine is made?

It is made from ribose-5-phosphate.