Chapter 5, part B Microbial Metabolism

Figure 5.11 Overview of Respiration and Fermentation

Fermentation O 2 is not required in fermentation. Does not use the Krebs cycle or ETC Electrons removed from the substrate reduce NAD+ to NADH. The final electron acceptor is an endogenous organic molecule. Produces only small amounts of ATP (one or two ATP molecules for each molecule of starting material) ATP molecules are produced by substrate- level phosphorylation. Fermentation releases energy from sugars or other organic molecules by oxidation. Pyruvate is metabolized to various compounds

Alcohol fermentation - acetaldehyde is reduced by NADH to produce ethanol. –Product - ethyl alcohol + CO 2 (gas) Lactic acid fermentation (homolactic)- pyruvic acid is reduced by NADH to lactic acid. –Product - lactic acid only Heterolactic fermentation –Product - lactic acid as well as other acids and alcohols. Fermentation

Figure 5.18b

Fermentation test Figure 5.23 Medium: Carbohydrate Mannitol, inverted Durham tube Products: Acid and gas.. Control tube S.epidermidis S.aureus E.coli Fermentation tests are used to determine the substrates the organism can metabolize by the products it generates.

Lipid Catabolism Lipases hydrolyze lipids into glycerol and fatty acids. Fatty acids and other hydrocarbons are catabolized by beta-oxidation. Catabolic products can be further broken down in glycolysis and the Krebs cycle. Figure 5.20 (hydrolase)

Protein Catabolism Protein Amino acids Extracellular proteases Krebs cycle Deamination, decarboxylation, dehydrogenation Organic acid Urea NH 3 + CO 2 Urease

Catabolism Highly reduced complex molecules NAD + NADH ADP ATP Energy Oxidized

Polysaccharide Biosynthesis Metabolic Pathways of Energy Use Anabolism Figure 5.28 ADPG (adenosine diphosphoglucose). UGPG (uridine diphosphoglucose) UDPNAc ( UDP-N-acetylglucoseamine)

Lipid Biosynthesis – Lipids are synthesized from fatty acids and glycerol. Glycerol is derived from dihydroxyacetone phosphate. Fatty acids are built from acetyl CoA. Metabolic Pathways of Energy Use Figure 5.29

Metabolic Pathways of Energy Use Amino Acid and Protein Biosynthesis All amino acids can be synthesized either directly or indirectly from intermediates of carbohydrate metabolism, particularly from the Krebs cycle. Figure 5.30a

Purine and Pyrimidine Biosynthesis. – The sugars composing nucleotides are derived from either the pentose phosphate pathway or the Entner-Doudoroff pathway. –Carbon and nitrogen atoms from certain amino acids form the backbones of the purines and pyrimidines Metabolic Pathways of Energy Use Figure 5.31

Reversible Reactions Can readily go in either direction. Each direction may need special conditions. A + B NADH [Substrate concentration]  AB NAD+ [Product concentration]

Amphibolic pathways Anabolic and catabolic reactions are integrated through a group of common intermediates. Both anabolic and catabolic reactions also share some metabolic pathways, such as Krebs Such integrated metabolic pathways are referred to as amphibolic pathways.

Phototrophs - Photosynthesis Energy from sunlight is used to convert carbon dioxide( CO 2 ) and water (H 2 O) into organic materials to be used in cellular functions such as biosynthesis and respiration Photo: Conversion of light energy into chemical energy (ATP) –Light-dependent (light) reactions Synthesis: Fixing carbon into organic molecules –Light-independent (dark) reaction, Calvin-Benson cycle Process is localized in chloroplasts (eukaryotes) or chlorosomes (prokaryotes)

Cyclic Photophosphorylation - the electrons return to the chlorophyll Figure 5.24a Light-dependent (light) reactions Noncyclic photophosphorylation - The electrons are used to reduce NADP + and form NADPH -The electrons from: -H 2 O or H 2 S replace those lost from chlorophyll (H 2 S) (S)(S)

Photosynthesis Oxygenic: 6CO H 2 O + Light energy  C 6 H 12 O O 2 + 6H 2 O Anoxygenic: 6CO H 2 S + Light energy  C 6 H 12 O S + 6 H 2 O

Figure 5.25 Light-independent (dark) reaction Photosynthesis: Fixing carbon (CO 2 ) into organic molecules Calvin-Benson cycle Use NADPH as cofactor Characteristic of: - Cianobacteria, - Green and Purple bacteria - Algae and Plants Autotrophs: Carbon dioxide (CO 2 ) is used as source of carbon

A Summary of Energy Production Mechanisms Nutritional types of organisms by Sources of energy Chemotrophs: Bond energy is released from a chemical compound Phototrophs: Light is absorbed in photo receptors and transformed into chemical energy.

Chemotrophs - Organisms that use energy from organic chemicals Heterotrophs: Organic compounds are metabolized to get carbon for growth and development. Cannot fix carbon Glucose Pyruvic acid NAD + NADH ETC ADP + PATP Chemoheterotrophs

Use energy from inorganic chemicals Energy is used in the Calvin-Benson cycle to fix CO 2 Chemoautotroph – Thiobacillus ferrooxidans 2Fe 2+ 2Fe 3+ NAD + NADH ETC ADP + PATP 2 H + Chemoautotrophs

Chlorophyll Chlorophyll oxidized ETC ADP + PATP Phototrophs Use Energy from sunlight Energy is used in the Calvin-Benson cycle to fix CO 2 – Photoautotrophs Energy is used in anabolism (carbon from organic compounds) - Photoheterotrophs

A nutritional classification of organisms

Metabolic Diversity Among Organisms Nutritional type Energy source Carbon source Example PhotoautotrophLightCO 2 Oxygenic: Cyanobacteria plants. Anoxygenic: Green, purple bacteria. PhotoheterotrophLightOrganic compounds Green, purple nonsulfur bacteria. ChemoautotrophChemicalCO 2 Iron-oxidizing bacteria. Chemoheterotroph ChemicalOrganic compounds Fermentative bacteria. Animals, protozoa, fungi, bacteria.

Carbon cycleNitrogen cycle Sulphur cycle Phosphorus cycle

Staphylococcus aureus Pseudomonas aeruginosa Bacillus subtilis Kelbsiella pneumonia Biochemical tests and bacterial identification Gram stain K. pneumonia and Ps. aeruginosa look alike through a microscope after Gram stain; so how can they be differentiated? Different species produce different enzymes determine what type of metabolic reactions an organism can carry out –Oxygen requirements –Fermentation –Enzymes of respiration –Amino acid catabolizing enzymes

Toxic Forms of Oxygen Singlet oxygen: O 2 boosted to a higher-energy state Superoxide free radicals: O 2 – Peroxide anion: O 2 2– Hydroxyl radical (OH  )

Chemical Requirements Oxygen (O 2 )

Dichotomous Key A dichotomous key is a series of questions which leads to the identification of an item. – a device on paper or computer that aids identification of a species or other type of entity. Dichotomous keys are used for the identification of organisms. A dichotomous key works by offering two alternatives at each juncture, and the choice of one of those alternatives determines the next step.

Learning objectives Describe the chemical reactions of, and list some products of, fermentation. Describe how lipids and proteins undergo catabolism. Provide two examples of the use of biochemical tests to identify bacteria. Compare and contrast cyclic and noncyclic photophosphorylation. Compare and contrast the light-dependent and light-independent reactions of photosynthesis. Compare and contrast oxidative phosphorylation and photophosphorylation. Write a sentence to summarize energy production in cells. Categorize the various nutritional patterns among organisms according to carbon source and mechanisms of carbohydrate catabolism and ATP generation. Describe the major types of anabolism and their relationship to catabolism. Define amphibolic pathways