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Metabolism
– The sum total of all chemical reactions that occurin a cell
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Catabolic reactions (catabolism)
– Energy-releasing metabolic reactions
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Anabolic reactions (anabolism)
– Energy-requiring metabolic reactions
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Nutrients
– Supply of monomers (or precursors of)required by cells for growth
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• Carbon
- – Required by all cells
- – Typical bacterial cell ~50% carbon (by dry weight)
- – Major element in all classes of macromolecules
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– Heterotrophs use_____ carbon
organic
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– Autotrophs use _____ carbon
inorganic
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Nitrogen
- – Typical bacterial cell ~12% nitrogen(by dry weight)
- – Key element in proteins, nucleic acids, andmany more cell constituents
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Phosphorus (P)
- • Synthesis of nucleic acids and phospholipids
- -Macronutrients
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Sulfur (S)
- • Sulfur-containing amino acids (cysteine andmethionine)
- • Vitamins (e.g., thiamine, biotin, lipoic acid) and coenzyme A
- -Macromolecule
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Potassium (K)
- • Required by enzymes for activity
- • Also used as a compatible solute by many bacteria
- -Macronutrient
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Magnesium (Mg)
- • Stabilizes ribosomes, membranes, and nucleic acids
- • Also required for many enzymes
- -Macromolecule
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Calcium (Ca)
- • Helps stabilize cell walls in microbes
- • Plays key role in heat stability of endospores
- -Macromolecule
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Sodium (Na)
- • Required by some microbes (e.g., marinemicrobes)
- -Macromolecule
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Iron
- – Key component of cytochromes and FeS proteins involved in electron transport
- – Cells produce siderophores (iron-binding agents) to obtain iron from insoluble mineral form (Figure 4.2)
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Ferrous Iron
- Fe2+
- -Generally formed under anoxic conditions
- -soluble
- (2 of us)
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Ferric iron
- Fe3+
- -Generally formed under oxic conditions
- -exists as insoluble mineral
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Growth Factors
- – Organic compounds required in small amounts by certain organisms
- • Examples: vitamins, amino acids, purines, pyrimidines
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Vitamins
- • Most commonly required growth factors
- • Most function as coenyzmes
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Culture Media
- – Nutrient solutions used to grow microbes inthe laboratory
- Two broad classes:
- Defined media
- Complex media
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Defined media:
precise chemical composition is known
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Complex media:
composed of digests of chemically undefined substances (e.g., yeastand meat extracts.
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Pure culture:
culture containing only a single kind of microbe
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Contaminants:
unwanted organisms in a culture
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Cultures prepared on solid media
- -Solid media are prepared by addition of a gelling agent (agar or gelatin)
- – When grown on solid media, cells form isolated masses (colonies)
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redox reactions
- is used in synthesis of energy-rich compounds (e.g., ATP)
- -Redox reactions occur in pairs (two half reactions-donar and acceptor(redoxcouple);
- -Reduced substance of a redox couple with a more negative E0′ donates electrons to the oxidized substance of a redox couple with a more positive E0′
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Electron donor:
the substance oxidized in a redox reaction
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Electron acceptor:
the substance reduced in a redox reaction
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Reduction potential (E0′):
tendency to donate electrons – Expressed as volts (V). the more negative E0' donates
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Redox tower
- -represents the range of possible reduction potentials
- • The reduced substance at the top of the tower donates electrons (is oxidized)
- • The oxidized substance at the bottom of the tower accepts electrons(is reduced)
- • The farther the electrons “drop,” the greater the amount of energy released
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Electron carriers (2 classes)
- -intermediates involved in Redox reactions
- -Electron carriers are divided into two classes
- – Prosthetic groups (attached to enzymes- not diffusable ex: heme,FeS)
- – Coenzymes (diffusible)
- • Examples: NAD+, NADP (Figure 4.10 )
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redox reaction energy storage (4 options)
- Primarily:
- – ATP; the prime energy currency
- – Phosphoenolpyruvate
- – Glucose 6-phosphate
- • Chemical energy also stored in coenzyme A
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