Chapter 2 1 amino acid biosynthesis 2014819

04/25/2023 by TDLV 2Content – Amino acid biosynthesis • Essential amino acid EAA: ensentials • Non essential amino acid NEAA: nonessentials • EAA biosynthesis • NEAA biosynthesis... Pol

CHAPTER 1: PROTEIN

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Content

– Amino acid biosynthesis

• Essential amino acid (EAA: ensentials)

• Non essential amino acid (NEAA:

nonessentials)

• EAA biosynthesis

• NEAA biosynthesis

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20 AMINO ACIDS

Polar R groups make the amino acid hydrophilic

Non-polar R groups make the amino acid hydrophobic

Ionic R groups make the amino acid hydrophilic

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AMINO ACID

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GENETIC CODE

Modified or Unusual Amino Acids

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GENES AND PROTEINS

Fig The flow of genetic information in prokaryotes (left) and

eukaryotes (right)

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The Nitrogen cycle (fixation)

Nitrogen fixation by:

• Lightning

• Bacteria

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Nitrogen cycle (fixation)

Bacteria-plant: symbiotic

Bacteria get ATP from plant

Plant get NH4+ from bacteria

Nitrifying Bacteria

"Oxidation"

Assimilation of Ammonia

• Generate metabolites: glutamate or glutamine

(At pH 7, ammonium ion predominates (NH4 +))

• At enzyme ‘s active site, unprotonated NH3 is the nucleophilic

Glutamate  glutamine

• glutamine synthetase

Glutamine  glutamate Prokaryotes & plants

Glutamate synthase transfers a nitrogen to a-ketoglutarate

Alternate amino acid production

in prokaryotes

Especially used if [NH3] is low Km of Gln

synthetase lower than Km of Glu dehydrogenase

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Amino acid biosynthesis (anabolism)

 Non-essential amino acids: synthesized from the products of their

 Essential amino acids: synthesized in micro-organisms (bacteria and

yeasts) and passed through the food chain until they reach us in our diet

 a-ketoacids are not common intermediates (enzymes needed to form them are lacking); they are present in micro-organisms and plants

 fixation of atmospheric nitrogen (by bacteria): inorganic nitrate

amino groups in amino acids

AMINO ACID BIOSYNTHESIS

• NONESSENTIAL AMINO ACIDS: 10 aa

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Pyruvate  alanine

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a-keto glutarate  glutamate

glutamate  glutamine

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Aspartate  asparagine

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Glutamate  arginine, proline

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3-phosphoglycerate  serine

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Serine  glycine

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Serine  cysteine

SYNTHESIS OF ESSENTIAL AMINO ACIDS

• PATHWAYS ONLY IN MICROORGANISMS AND PLANTS

– probable evolutionary loss in mammals

– pathways are very complicated

– actual pathways vary across species!

• in contrast to lipid and carbohydrate pathways, which are almost universal

• SYNTHESIZED FROM COMMON METABOLIC PRECURSORS

– aspartate

– pyruvate

– Erythrose-4-phosphate & phosphoenolpyruvate

– purine + ATP (histidine)

BIOSYNTHESIS OF ESSENTIAL AMINO ACID: 10 aa

• Four “families”

– ASPARTATE

• LYS: lysin /ai/

• THR: threonine /ɵri/

– PYRUVATE

• LEU, ILE, VAL (the “branched chain” amino acids)

– Erythrose-4-phosphate & Phosphoenolpyruvate for AROMATIC

amino acids

• TYR /ai/ (conditionally essential)

• TRP: tryptophane /trip/

– ATP + Glutamate + Glutamine + phosphoribosyl pysophosphate :

HISTIDINE /his/

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Biosynthesis of Amino Acids

Highlight : precursors : intermediates in glycolysis, TCA cycle, pentose phosphate

Methionine + ATP  methionine

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Homocysteine  methionine

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Erythrose-4-phosphate & Phosphoenolpyruvate for AROMATICS

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Synthesis of Chorismate

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Phenylalanine  tyrosine

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ATP + Glutamate + Glutamine + phosphoribosyl pysophosphate 

histidine

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Pyruvate  Leucine

Leucine inhibits its own synthesis

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Pyruvate  Leucine

• Leucine regulates its own synthesis by inhibiting in earlier steps

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Synthesis of Isoleucine, Valine

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Synthesis of Lysine, Threonine