CH 14: Nitrogen metabolism

What is the role of nitrogen in biomolecules?

Nitrogen is found in amino acids, nitrogenous bases, porphyrins, and several lipids.

What is nitrogen fixation?

The conversion of inert nitrogen gas into a useful form such as NH3, which requires significant energy and is performed by specific prokaryotic microorganisms.

Which species are known to live in symbiosis with plants for nitrogen fixation?

Rhizobium species.

What types of organisms are Azotobacter vinelandii and Clostridium pasteurianum?

They are free-living nitrogen-fixing organisms found in water.

How do plants obtain nitrogen?

Plants absorb NH3 and NO3 from the soil, synthesized by bacteria or provided by fertilizers.

Why is the amide group of glutamine important in plants?

It is used to synthesize other carbon-containing nitrogen compounds like amino acids, nucleotides, and nucleic acids.

What are non-essential amino acids (NAA)?

Amino acids that animals can synthesize on their own.

What are essential amino acids (EAA)?

Amino acids that animals must obtain from their diet.

Describe the flow of nitrogen in an ecosystem.

It flows from nitrogen fixation by bacteria to plants, to animals, to waste, and back to microorganisms.

What are metabolic mechanisms for amino acids?

Processes that adjust amino acid concentrations and degrade excess amounts of NAA and EAA.

What are branched amino acids?

Certain essential amino acids like leucine, isoleucine, and valine that remain unchanged in concentration and are used for synthesizing many non-essential amino acids.

What is transamination?

A dominant chemical reaction in amino acid metabolism, catalyzed by aminotransferases, where an alpha-amino group is transferred from an alpha-amino acid to an alpha-keto acid.

What is required for nitrogen fixation?

At least four molecules of ATP and a series of electron transfers to form 2NH3.

What enzyme catalyzes nitrogen fixation in prokaryotes?

The nitrogenase complex.

What is the nitrogenase complex made of?

It consists of a nitrogenase protein and a nitrogenase reductase protein, which contain molybdenum and iron atoms.

What happens if oxygen is present during nitrogen fixation?

Both components of the nitrogenase complex are irreversibly inactivated by oxygen.

What are heterocysts?

Specialized cells in aerobic nitrogen-fixing bacteria that contain nitrogenase.

What is the function of leghemoglobin in legumes?

It traps oxygen to prevent it from interacting with the nitrogenase complex.

What are amino acids?

Building blocks of proteins and sources of nitrogen in synthetic pathways.

What is the amino acid pool?

The collection of amino acid molecules that are immediately available for metabolic processes.

How are amino acids transported into cells?

Through specific membrane-bound transport proteins.

What is the process of synthetic reactions of amino acids?

Amino groups are available for reactions including transamination and direct incorporation of NH4+ groups into amino acids.

What are the two types of eukaryotic transamination?

Type one donates an alpha-amino group, while type two accepts an alpha-amino group, often using glutamate.

What is the significance of the a-ketoglutarate/glutamate pair?

They are involved in reversible transamination reactions, important in amino acid metabolism.

What means are used to incorporate NH4 ions into amino acids?

Reductive amination of alpha-keto acids and formation of amides of aspartic and glutamic acids.

How are amino acids synthesized in animals?

Unique pathways that generally derive from glycerate-3-phosphate, pyruvate, alpha-ketoglutarate, or oxaloacetate.

What is an exception to amino acid synthesis?

Tyrosine, which is synthesized from the essential amino acid phenylalanine.

Which amino acids are included in the glutamate family?

Glutamate, glutamine, proline, and arginine.

What catalyzes the conversion of glutamate to glutamine?

Glutamine synthase.

What type of reaction occurs to produce proline from glutamate?

A transamination reaction, regulated by feedback inhibition.

How is arginine synthesized?

It begins with acetylation of glutamate, leading to the formation of ornithine and then arginine through the urea cycle.

What amino acids are included in the serine family?

Serine, glycine, and cysteine.

What is serine a precursor of?

Ethanolamine and sphingosine.

What role does glycine play in the serine family?

It is used in purine, porphyrin, and glutathione synthesis pathways.

What role does serine have in the serine family?

Synthesized directly from glycerate-3-phosphate and regulated by feedback inhibition.

How is cysteine biosynthesized in the serine family?

Its carbon skeleton is derived from serine, while the sulfhydryl group is transferred from methionine.

What are neurotransmitters?

Substances that can be either excitatory or inhibitory, many of which are amino acids or their derivatives.

What are biogenic amines?

Amino acid derivatives that act as neurotransmitters.

Which neurotransmitters are derivatives of tyrosine?

Dopamine, norepinephrine, and epinephrine.

What is the role of dopamine and norepinephrine in the brain?

They act as excitatory neurotransmitters.

What neurotransmitter is formed from the decarboxylation of glutamate?

GABA, which acts as an inhibitory neurotransmitter.

What is serotonin synthesized from?

Tryptophan, and it regulates feeding behavior.

What does histamine do in the body?

Mediates allergic reactions, stimulates gastric acid production, and functions as a neurotransmitter.

What role does nitric oxide (NO) play in the body?

It dilates blood vessels, inhibits platelet aggregation, and is linked to neurotransmitter functions in the brain.