Chapter 5 Microbial Metabolism Part 3

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

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

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

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

Alcohol fermentation –Produces 2 ethyl alcohol (ethanol) + 2 CO 2 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

Figure 5.18b

Fermentation Figure 5.23

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

Lipid Catabolism Figure 5.20 Oxidation of glycerol and fatty acids Beta oxidation: oxidation of fatty acids

Lipid and Protein Catabolism Proteins = amino acids (peptide bonds) Proteases & peptidases: extracellular enzymes that break down proteins into amino acids component Fig summary of carbohydrates, lipids, and protein catabolisms

ProteinAmino 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 (NH 4 + ) (can be excreted from the cell)

Protein Catabolism Figure 5.22

Biochemical tests Figure 10.8 Used to identify bacteria and yeasts. –Designed to detect the presence of enzymes

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

Carbon fixation: synthesis of sugars by using carbons from CO 2 gas (from the atmosphere) Recycling of C by cyanobacteria, algae, and green plants via photosynthesis Table 5.6 for summary

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)

Photophosphorylation Light-dependent (light) reactions –ADP + P + light energy ATP (chemiosmosis) –NADP reduced to NADPH –cyclic photophosphorylation –noncyclic photophosphorylation More common process

Figure 5.24a Cyclic Photophosphorylation Electron eventually return to chlorophyll

Figure 5.24b Noncyclic Photophosphorylation Electrons become incorporated into NADPH

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 CO 2 to synthesize sugars (carbon fixation) –complex cyclic pathway

Figure 5.25 The Calvin-Benson Cycle Go through 6 cycles to produce one glucose. 6 CO 2 18 ATP + 12 NADPH = 1 Glucose * Shows 3 cycles.

Fig Summary

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 CO 2 as C source heterotrophs (organotrophs): feed on others; require an organic source of C

Phototrophs Use light as energy source. Photoautotrophs use energy in the Calvin- Benson cycle to fix CO 2 ; oxygenic & anoxygenic. Photoheterotrophs use organic compounds as C source; anoxygenic. Chlorophyll Chlorophyll oxidized ETC ADP + P ATP

Photosynthetic process in photoautotrophs Oxygenic (produces O 2 ): –H atoms of H 2 O are used to reduce CO 2 to form organic compounds, and O gas is given off Anoxygenic (does not produce O 2 ): –typical of cyclic photophosphorylation; anaerobic reaction –use sulfur, sulfur compounds, or hydrogen gas to reduce CO 2 to form organic compounds

Chemotrophs Use chemical compounds as energy source. –Redox reactions of inorganic or organic compounds Chemoautotroph e.g. Thiobacillus ferroxidans –Inorganic source of energy; CO 2 is C source Energy used in the Calvin-Benson cycle to fix CO 2. 2Fe 2+ 2Fe 3+ NAD + NADH ETC ADP + PATP 2 H +

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 + PATP

Metabolic Diversity Among Organisms Fermentative bacteria. Animals, protozoa, fungi, bacteria. Iron-oxidizing bacteria. Green, purple nonsulfur bacteria. Oxygenic: Plants, cyanobacteria, algae Anoxygenic: Green, purple bacteria. Example Organic compounds Chemical Chemo- heterotroph CO 2 Organic compounds CO 2 Carbon source Chemical Chemoautotroph Light Photoheterotroph Light Photoautotroph Energy sourceNutritional type

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

Polysaccharide Biosynthesis Metabolic Pathways of Energy Use Use intermediates produced during glycolysis and the Krebs cycle & from lipids or amino acids. Figure 5.28

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

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

Amino Acid and Protein Biosynthesis Metabolic Pathways of Energy Use Figure 5.30a Protein synthesis from amino acids involves dehydration and ATP.

Amino Acid and Protein Biosynthesis –transamination: transfer of amino group from a preexisting amino acid Metabolic Pathways of Energy Use Figure 5.30b

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

Integration of Metabolism Catabolic and anabolic reactions are joined through a group of common intermediates & share some metabolic pathways (e.g. Krebs cycle)

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

Amphibolic pathways Figure