Anabolism

1
Anabolism

• Microbiology February 7, 2005
• Chapter 10

2
Anabolism overview

• What to do with energy generated from
  respiration, photosynthesis or fermentation?
• Synthesize sugars
• Calvin Cycle, gluconeogenesis
• Synthesize other building blocks
• assimilation of N and S
• amino acids, nucleotides, lipids
• Synthesize Macromolecules
• peptidoglycan
• proteins, nucleic acids

3
Autotrophy Carbon Fixation

• reduction from inorganic CO2 to organics
• requires energy (ATP) and reducing power NAD(P)H
• How do organisms do it?
• chemolithotrophs - oxidize inorganics for energy,
  use some of this energy to reverse e- flow and
  reduce NAD(P).
• anoxygenic phototrophs
• non-sulfur - cyclic photophosphorylation for
  energy, use energy to reverse e- flow (from
  succinate) and reduce NAD(P). - Rhodobacter
• sulfur bacteria - cyclic photophosphorylation for
  energy, non-cyclic e- flow (from inorganics) to
  reduce NAD(P) - Chlorobium

4
Autotrophy Carbon Fixation

• oxygenic phototrophs - non-cyclic (from H2O)
  photophosphorylation for energy, non-cyclic e-
  flow (from PS II) to reduce NAD(P) -
  cyanobacteria, prochloron
• water split, donates electrons to P680, oxygen
  produced
• P680 excited, electrons passed to pheophytin,
  quinones, cytochrome, plastocyanin, P700
• P700 excited, electrons passed to FeS protein,
  ferredoxin, NADP

5
Calvin Cycle

• What is the most abundant enzyme on earth?
• What is it's other claim to fame - poor
  efficiency - 2 CO2 fixed/sec. Why?
• Enzyme evolved before oxygenic photosynthesis -
  reducing atmosphere -oxygen causes side reaction
• Carbon fixation (autotrophy) - Calvin cycle in
  most organisms
• RUBISCO - ribulose bisphosphate carboxylase
  oxygenase
• 6 RuBP (5C) 6 CO2 --gt 12 phosphoglycerate
  --gt--gtF-6-P (6C) 6 RuBP
• reactions similar to pentose phosphate pathway
• Synthesis of 1 glucose requires 18 ATP, 12 NADPH

6
Gluconeogenesis

• Synthesis of sugars from pyruvate or TCA cycle
  intermediates (oxaloacetate)
• Reverse of glycolytic reactions except for key
  regulated steps
• Pyruvate --gt PEP
• F-1,6, bis-phosphate --gtF-6-phosphate
• Glucose-6-P --gt glucose

7
Sulfur Metabolism

• Sulfur - sulfate activated by linking to adenine
  nucleotide to form PAPS.
• Used to synthesize cysteine after reduction to
  sulfide.

8
Nitrogen metabolism

• Different Nitrogen sources
• from ammonia - aKG?glutamate?glutamine pathway
  followed by transamination reactions (nitrogen
  currency)
• from nitrate - Assimilatory nitrate reduction
  (using NADPH), via nitrite.
• Nitrogen fixation N2?ammonia Azotobacter,
  Rhizobium, cyanobacteria

9
Peptidoglycan synthesis

• Sugars are activated for polysaccharide
  synthesis by linking to a nucleotide(e.g.
  UDP-glucose)
• Activated sugars are then often modified
• Amino (glucosamine)
• Acetyl (N-Acetyl glucosamine)
• Carboxylic acid (N-acetyl muramic acid)
• Peptidoglycan building blocks synthesized on
  bactoprenol carrier.

10
Peptidoglycan Synthesis

• Recycling of bactoprenol inhibited by antibiotic
  bacitracin
• Transpeptidation varies between gram and gram
  
• Inhibited by penicillin
• New peptidoglycan synthesis occurs mainly in
  septal area