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Metabolism:
Fueling Cell Growth
Chapter 6
Metabolism
- (^) Cells must accomplish two fundamental tasks
to grow
- (^) Synthesize new components
- (^) Harvest energy
- (^) The sum total of chemical reactions of
biosynthesis and energy-harvesting is termed
metabolism
- (^) Energy defined as capacity to do work
- (^) Exists as
- (^) Potential energy
- (^) Kinetic energy
» Doing work
Harvesting energy
- (^) Amount of energy available released from bonds is
free energy
- (^) Energy available to do work
- (^) If reactants have more free energy than
products, energy is released
- (^) If products have more energy than reactants,
energy is consumed
Central Metabolic Pathways
- (^) Pathways modify organic molecules to form
- (^) High energy intermediates to synthesize ATP
- (^) Intermediates to generate reducing power
- (^) Intermediates and end products as precursor metabolites
- (^) Pathways (^) Glycolysis (^) Pentose Phosphate Pathway (^) Tricarboxylic Acid Cycle
Scheme of Metabolism
Fermentation
- (^) Used by organisms that cannot respire
- (^) Due to lack of suitable inorganic electron acceptor or lack of electron transport chain
- (^) Fermentation stops short of oxidizing glucose or other organic compounds completely, and instead uses an organic intermediate such as pyruvate or a derivative as an electron acceptor
- (^) Fermentation is partial oxidation of glucose, produces very little ATP; ATP produced only in glycolysis
End products of fermentation pathways E. coli
Chemolithotrophs
- (^) Chemolithotrophs able to use reduced inorganic chemicals as source of energy
- (^) These organisms fall into four groups
- (^) Hydrogen bacteria
- (^) Sulfur bacteria
- (^) Oxidize hydrogen sulfide (H 2 S)
- (^) Iron bacteria
- (^) Nitrifying bacteria
- (^) Two groups
- (^) One oxidizes ammonia (NH 3 ) to nitrite
- (^) One oxidizes nitrite (NO 2 −) to nitrate (NO 3 −)
- (^) Chemolithotrophs generate ATP through oxidative
phosphorylation
- (^) Organisms thrive in specific environments
- (^) Particularly where reduced inorganic compounds are found
- (^) Do not require external carbon source
- (^) Produce organic carbon from inorganic source through carbon fixation (Carbon dioxide converted to organic carbon)
- (^) Pigments include
- (^) Chlorophyll
- (^) Found in plants, algae and cyanobacteria
- (^) Bacteriochlorophylls
- (^) Found in purple and green photosynthetic bacteria
- (^) Accessory pigments
- (^) Reaction center pigments
- (^) Function as electron donors
- (^) Antennae pigments
Photosynthetic organisms highly visible due
to light capturing pigments
- (^) Light reactions accomplish two tasks
- (^) Synthesize ATP through photophosphorylation
- (^) Generate reducing power to fix carbon dioxide
Anabolic Pathways
- (^) Synthesis of subunits from precursor metabolites
- (^) Pathways consume ATP, reducing power and precursor metabolites
- (^) Make macromolecules once subunits are synthesized
- (^) Different macromolecules can be joined to form the structures making up the cell
- (^) Lipid synthesis
- (^) Amino acid synthesis
- (^) Nucleotide synthesis
Nucleotides are composed of three units
- Nitrogenous base
- (^) Purine (adenine and guanine) – A, G
- (^) Pyrimidine (thymine and cytosine) – T, C
- 5-carbon sugar molecule (deoxyribose)
- Phosphate molecule
Nucleotides bond covalently between the 5’PO 4 of one nucleotide and the 3’OH of another
DNA made up of deoxy-ribo-nucleotides