Chapter 2 1 amino acid biosynthesis 2014819

CHAPTER 1: PROTEIN


Content
– Amino acid biosynthesis
• Essential amino acid (EAA: ensentials)
• Non essential amino acid (NEAA:
nonessentials)
• EAA biosynthesis
• NEAA biosynthesis

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by TDLV

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20 AMINO ACIDS

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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


AMINO ACID

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by TDLV

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GENETIC CODE

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by TDLV

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Modified or Unusual Amino Acids



GENES AND PROTEINS

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Fig.

by TDLV
The flow of genetic information
in prokaryotes (left) and
eukaryotes (right)

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Nitrogen acquisition
• Nitrogen Fixation
• Nitrate Assimilation
• Ammonium Assimilation

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by TDLV

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The Nitrogen cycle (fixation)
Nitrogen fixation by:
• Lightning
• Bacteria

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by TDLV

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Nitrate Assimilation

(Green plants, some fungi and bacteria)

NO3– + NADH + H+

NO2– + 8H+ + 6e–

Nitrate Reductase

Nitrite Reductase

NO2– + H2O + NAD+

NH4+ + 2H2O


Nitrogenase
• Present in Rhizobium bacteria that live in root
nodules of leguminous plants
• Some free-living soil and aquatic bacteria also
possess nitrogenase
• Nitrogenase reaction:
N2 + 8 H+ + 8 e- + 16 ATP
2 NH3/NH4+ + H2 + 16 ADP + 16 Pi
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by TDLV

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Nitrogen cycle (fixation)

Bacteria-plant: symbiotic
Bacteria get ATP from plant
Plant
get NH4+ from bacteria
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by TDLV

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Nitrifying Bacteria

NH3

"Oxidation"

NO3

–


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


Ammonia  Glutamate
• amination of a-ketoglutarate
by glutamate dehydrogenase
occurs in plants, animals and microorganisms


Glutamate  glutamine
• glutamine synthetase


Glutamine  glutamate

Prokaryotes & plants

Glutamate synthase transfers a nitrogen to a-ketoglutarate