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Chapter 5: Microbial Metabolism
Metabolism
Collection of controlled biochemical reactions that take place within cells of an
organism
The ultimate function of metabolism is to reproduce the organism
Metabolic processes guided by 8 elementary statements
1. Every cell acquires nutrients
2. Metabolism requires energy from light or from catabolism of nutrients
3. Energy is stored in adenosine triphosphate (ATP)
4. Cells catabolize nutrients to form precursor metabolites
5. Precursor metabolites, energy from ATP, and enzymes used in anabolic
reactions
6. Enzymes plus ATP form macromolecules
7. Cells grow by assembling macromolecules into cellular structures
8. Cells reproduce once they have doubled in size
Basic Chemical Reactions Underlying Metabolism
Catabolism and Anabolism
-catabolic pathways:
-anabolic pathways:
Oxidation and Reduction Reactions (redox reactions)
-Transfer of electrons from molecule that donates electron to molecule that
accepts electrons
-These reactions are always coupled
-Cells use electron carrier molecules to carry electrons (often in H atoms)
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-Three important electron carriers:
▫Nicotinamide adenine dinucleotide (NAD+) → NADH
▫Nicotinamide adenine dinucleotide phosphate (NADP+) → NADPH
▫Flavine adenine dinucleotide (FAD) → FADH2
ATP Production and Energy Storage
-Phosphorylation-Cells phosphorylate ADP to ATP in three ways
1)
2)
3)
-Anabolic pathways use some energy of ATP by breaking a phosphate bond
*Please review the Enzymes section if you feel “rusty” on enzyme function*
Carbohydrate Catabolism
Glycolysis-
Cellular Respiration-
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-Composed of three stages; synthesis of Acetyl-CoA, Krebs Cycle, and the
Electron Transport Chain.
-Synthesis of acetyl-CoA-
-Krebs Cycle-
-Electron Transport Chain-
-in aerobic respiration, oxygen is the final electron acceptor
-in anaerobic respiration, molecules other than oxygen are the final
electron acceptors.
- chemiosomosis-
-ATP-synthase-
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Alternatives to Glycolysis- Glucose can be catabolized in alternate pathways.
-Pentose Phosphate Pathway-
-Entner-Doudoroff Pathway-
Fermentation-occurs when cellular respiration pathways are blocked, usually resulting
from the lack of a final electron receptor.
-pyruvic acid is the starting point for fermentation
-the essential function of fermentation is the regeneration of NAD+ for
glycolysis, so that ADP molecules can be phosphorylated to ATP
-common fermentation end products:
-some bacteria can only ferment certain substances, this can be used for
identification.
*Other Catabolic Pathways will not be covered in Lecture*
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Photosynthesis
Chemicals and Structures
-chlorophyll-photosystems-thylakoids-
Light-Dependent Reactions- absorption of light, pumping of protons, and
production of ATP, can occur in two different pathways:
-cyclic photophosphorylation-
-noncyclic photophosphorylation-
Light-Independent Reactions- uses the ATP, NADPH, and CO2 to produce 6
carbon molecules (glucose)
-Calvin-Benson Cycle-
*Other Anabolic Pathways will not be covered in Lecture*
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