chapter 5 microbial metabolism part 3. first stage: glycolysis second stage: reduced coenzymes (nadh...
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Chapter 5
Microbial Metabolism
Part 3
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• First stage: Glycolysis
• Second stage: Reduced coenzymes (NADH & NADPH) donate their e- and H+ to pyruvic acid and its derivatives to form a fermentation end products.
Fermentation
Fig. 5.18a
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• Releases energy from oxidation of organic molecules– sugars, amino acids, organic acids, purines, and
pyrimidines
• Does not require oxygen– bun can occur with oxygen
• Does not use the Krebs cycle or ETC
Fermentation
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Fermentation
• Uses an organic molecule as the final electron acceptor
• Produces only small amounts of ATP – produced only during glycolysis– much of the energy remain in the chemical
bonds of the organic end-products
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Figure 5.19
Fermentation
• Second stage of fermentation ensures a steady supply of NAD+ & NADP+ so that glycolysis can continue
– regeneration of NAD+ & NADP+ during fermentation can enter another round of glycolysis
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• Alcohol fermentation– Produces 2 ethyl alcohol (ethanol) + 2 CO2
• Lactic acid fermentation– Produces lactic acid; can result in food
spoilage– Homolactic (homofermentative) fermentation:
produces lactic acid only.– Heterolactic (heterofermentative) fermentation:
produces both lactic acid and other compounds (e.g. alcohol).
• Use pentose phosphate pathway
Fermentation
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Fermentation
Figure 5.18b
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Fermentation
Figure 5.23
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Lipid and Protein Catabolism
• Lipids and proteins are oxidized for energy production (sources of electrons & protons for respiration)
• Lipids (fats) = fatty acids + glycerol (ester linkage)
• Lipases: extracellular enzymes that degrade fats into fatty acid and glycerol components
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Lipid Catabolism
Figure 5.20
Oxidation of glycerol and fatty acids
Beta oxidation: oxidation of fatty acids
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Lipid and Protein Catabolism
• Proteins = amino acids (peptide bonds)
• Proteases & peptidases: extracellular enzymes that break down proteins into amino acids component
• Fig. 5.21 summary of carbohydrates, lipids, and protein catabolisms
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Protein Amino acids
Extracellular proteases
Krebs cycle
Deamination, decarboxylation, dehydrogenation
Organic acid
Protein Catabolism
• Deamination: removal of an amino group from an amino acid to form an ammonium (NH4
+) (can be excreted from the cell)
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Protein Catabolism
Figure 5.22
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Biochemical tests
Figure 10.8
• Used to identify bacteria and yeasts.– Designed to
detect the presence of enzymes
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• Used by plants and many microbes to synthesize complex organic compounds from simple inorganic substances
• Photo: Conversion of light energy into chemical energy (ATP)– Light-dependent (light) reactions
• Synthesis: assembly of organic molecules (using chemical energy)– Light-independent (dark) reaction, Calvin-Benson
cycle
Photosynthesis
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Photosynthesis
• Carbon fixation: synthesis of sugars by using carbons from CO2 gas (from the atmosphere)
• Recycling of C by cyanobacteria, algae, and green plants via photosynthesis
• Table 5.6 for summary
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The Light-Dependent Reactions: Photophosphorylation
• Light energy is absorbed by chlorophyll in the photosynthetic cell excite some of the molecules’ electrons chemiosmotic proton pump– Chlorophyll a used by green plants, algae, and
cyanobacteria (in thylakoids)– Bacteriochlorophylls used by other bacteria
(chlorosomes, intracytoplasmic membrane)– Bacteriorhodopsin used by Halobacterium (purple
portion of plasma membrane)
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Photophosphorylation
• Light-dependent (light) reactions– ADP + P + light energy ATP (chemiosmosis)– NADP reduced to NADPH– cyclic photophosphorylation– noncyclic photophosphorylation
• More common process
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Figure 5.24a
Cyclic Photophosphorylation
• Electron eventually return to chlorophyll
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Figure 5.24b
Noncyclic Photophosphorylation
• Electrons become incorporated into NADPH
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The Light-Independent Reactions: The Calvin-Benson Cycle
• Light-independent (dark) reaction (Calvin-Benson cycle)– use ATP along with electron produced in light-
dependent reactions to reduce CO2 to synthesize sugars (carbon fixation)
– complex cyclic pathway
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Figure 5.25
The Calvin-Benson Cycle• Go through 6
cycles to produce one glucose.
6 CO2
18 ATP
+ 12 NADPH
= 1 Glucose
* Shows 3 cycles.
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Fig. 5.26
Summary
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Metabolic diversity Among Organisms
• All organisms can be classified metabolicaly according to their nutritional pattern– energy source: phototrophs vs. chemotrophs– carbon (C) source: autotrophs vs. heterotrophs
• autotrophs (lithotrophs): self-feeders; use CO2 as C source
• heterotrophs (organotrophs): feed on others; require an organic source of C
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Phototrophs• Use light as energy source.
• Photoautotrophs use energy in the Calvin-Benson cycle to fix CO2; oxygenic & anoxygenic.
• Photoheterotrophs use organic compounds as C source; anoxygenic.
Chlorophyll
Chlorophylloxidized
ETC
ADP + P ATP
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Photosynthetic process in photoautotrophs
• Oxygenic (produces O2):
– H atoms of H2O are used to reduce CO2 to form organic compounds, and O gas is given off
• Anoxygenic (does not produce O2):
– typical of cyclic photophosphorylation; anaerobic reaction
– use sulfur, sulfur compounds, or hydrogen gas to reduce CO2 to form organic compounds
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Chemotrophs• Use chemical compounds as energy source.
– Redox reactions of inorganic or organic compounds
• Chemoautotroph e.g. Thiobacillus ferroxidans
– Inorganic source of energy; CO2 is C source
• Energy used in the Calvin-Benson cycle to fix CO2.
2Fe2+
2Fe3+
NAD+
NADH
ETC
ADP + P ATP
2 H+
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Chemotrophs• ATP produced by oxidative phosphorylation
• Chemoheterotroph (fungi, protozoa, animals, & most bacteria)
– Energy source and C source are usually the same organic compound e.g. glucose
• saprophytes (use dead organic matter) vs. parasites (need living host)
• electrons from H atoms = energy source
Glucose
Pyruvic acid
NAD+
NADH
ETC
ADP + P ATP
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Metabolic Diversity Among Organisms
Fermentative bacteria.Animals, protozoa, fungi, bacteria.
Iron-oxidizing bacteria.
Green, purple nonsulfur bacteria.
Oxygenic: Plants, cyanobacteria, algaeAnoxygenic: Green, purple bacteria.
Example
Organic compounds
Chemical Chemo- heterotroph
CO2
Organic compounds
CO2
Carbon source
Chemical Chemoautotroph
Light Photoheterotroph
Light Photoautotroph
Energy sourceNutritional type
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Metabolic Pathways of Energy Use
• Most of the ATP used in the production of new cellular components– Also used to provide energy for active transport,
and flagellar motion
• Anabolism in autotrophs– carbon fixation via Calvin-Benson cycle require
both ATP& electrons
• Anabolism in heterotrophs– need ready source of organic compounds + ATP
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• Polysaccharide Biosynthesis
Metabolic Pathways of Energy Use
• Use intermediates produced during glycolysis and the Krebs cycle & from lipids or amino acids.
Figure 5.28
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• Lipid Biosynthesis– synthesized by
variety of routes– used for structural
component of membranes (e.g. phospholipids, cholesterol, waxes, carotenoids)
– also used in energy storage
Metabolic Pathways of Energy Use
Figure 5.29
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Amino Acid and Protein Biosynthesis
• Microbes with the necessary enzymes can either synthesize all amino acids directly or indirectly from intermediates of carbohydrate metabolism
• Others need preformed amino acids – Supplied from Krebs cycle
• amination: addition of an amino group
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• Amino Acid and Protein Biosynthesis
Metabolic Pathways of Energy Use
Figure 5.30a
• Protein synthesis from amino acids involves dehydration and ATP.
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• Amino Acid and Protein Biosynthesis– transamination: transfer of amino group from a
preexisting amino acid
Metabolic Pathways of Energy Use
Figure 5.30b
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• Purine and Pyrimidine Biosynthesis
Metabolic Pathways of Energy Use
Figure 5.31
• C and N atoms derived from amino acids form the purine & pyrimidine rings
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Integration of Metabolism
• Catabolic and anabolic reactions are joined through a group of common intermediates & share some metabolic pathways (e.g. Krebs cycle)
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• Are metabolic pathways that have both catabolic and anabolic functions.– Bridge the reactions that lead to the breakdown and
synthesis of carbohydrates, lipids, proteins, and nucleotides
Amphibolic pathways
Figure 5.32.1
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Amphibolic pathways
Figure 5.32.2