Microbial respiration
- 1. MICROBIAL RESPIRATION Dr. R. BALAGURUNATHAN Professor & Head Dept. of Microbiology Periyar University Periyar Palkalai Nagar Salem – 636 011.
- 2. Microbial Metabolism A. Basic Concepts of Metabolism B. Glycolytic Pathways C. Fermentation D. Respiration E. Photosynthesis F. Chemolithotrophy
- 3. Basic Concepts • Definitions – Metabolism: The processes of catabolism and anabolism – Catabolism: The processes by which a living organism obtains its energy and raw materials from nutrients – Anabolism: The processes by which energy and raw materials are used to build macromolecules and cellular structures (biosynthesis)
- 4. Basic Concepts Reduction and Oxidation –An atom becomes more reduced when it undergoes a chemical reaction in which it • Gains electrons • By bonding to a less electronegative atom • And often this occurs when the atom becomes bonded to a hydrogen
- 5. Basic Concepts Reduction and Oxidation - An atom becomes more oxidized when it undergoes a chemical reaction in which it • Loses electrons • By bonding to a more electronegative atom • And often this occurs when the atom becomes bonded to an oxygen
- 6. Basic Concepts Reduction and Oxidation In metabolic pathways, we are often concerned with the oxidation or reduction of carbon. Reduced forms of carbon (e.g. hydrocarbons, methane, fats, carbohydrates, alcohols) carry a great deal of potential chemical energy stored in their bonds. Oxidized forms of carbon (e.g. ketones, aldehydes, carboxylic acids, carbon dioxide) carry very little potential chemical energy in their bonds.
- 7. Basic Concepts Reduction and Oxidation Reduction and oxidation always occur together. In a reduction-oxidation reaction (redox reaction), one substance gets reduced, and another substance gets oxidized. The thing that gets oxidized is called the electron donor, and the thing that gets reduced is called the electron acceptor.
- 8. Basic Concepts Enzymatic Pathways for Metabolism – Metabolic reactions take place in a step-wise fashion in which the atoms of the raw materials are rearranged, often one at a time, until the formation of the final product takes place. – Each step requires its own enzyme. – The sequence of enzymatically-catalyzed steps from a starting raw material to final end products is called an enzymatic pathway (or metabolic pathway)
- 9. Basic Concepts Cofactors for Redox Reactions – Enzymes that catalyze redox reactions typically require a cofactor to “shuttle” electrons from one part of the metabolic pathway to another part. – There are two main redox cofactors: NAD and FAD. These are (relatively) small organic molecules in which part of the structure can either be reduced (e.g., accept a pair of electrons) or oxidized (e.g., donate a pair of electrons).
- 10. Basic Concepts Cofactors for Redox Reactions NAD(oxidized) + H+ + Pair of electrons NADH(reduced) FAD(oxidized) + H+ + Pair of electrons FADH(reduced) NAD and FAD are present only in small (catalytic) amounts – they cannot serve as the final electron acceptor, but must be regenerated (reoxidized) in order for metabolism to continue.
- 11. Basic Concepts ATP: A “currency of energy” for many cellular reactions – ATP stands for adenosine triphosphate. It is a nucleotide with three phosphate groups linked in a small chain. – The last phosphate in the chain can be removed by hydrolysis (the ATP becomes ADP, or adenosine diphosphate). This reaction is energetically favorable: it has a DG°' of about –7.5 kcal/mol ATP + H2O ® ADP + Phosphate + Energy (7.5 kcal/mol)
- 12. Respiration • Features of respiratory pathways – Pyruvic acid is oxidized completely to CO2. – The final electron acceptor is usually an inorganic substance. – NADH is oxidized to form NAD: Essential for continued operation of the glycolytic pathways. – O2 may or may not be required. • Aerobic respiration: O2 is the final e- acceptor. • Anaerobic respiration: An substance, usually inorganic, other than O2 is the acceptor (eg nitrate, nitrite, sulfate) – A lot of additional ATP are made (up to 36 per glucose molecule).
- 13. Respiration Stages of Respiration – Preliminary reactions and the Krebs cycle (TCA or Citric Acid Cycle) – Respiratory electron transport
- 15. Metabolism – An overview
- 16. Glycolytic Pathways • Features of glycolytic pathways – Partial oxidation of glucose to form pyruvic acid – A small amount of ATP is made – A small amount of NAD is reduced to NADH
- 17. Glycolytic Pathways Major glycolytic pathways found in different bacteria: – Embden-Meyerhoff-Parnas pathway • “Classic” glycolysis • Found in almost all organisms – Hexose monophosphate pathway • Also found in most organisms • Responsible for synthesis of pentose sugars used in nucleotide synthesis – Entner-Doudoroff pathway • Found in Pseudomonas and related genera – Phosphoketolase pathway • Found in Bifidobacterium and Leuconostoc
- 18. Overview of Cell Metabolism
- 19. – After Sugars are made or obtained, they are the major energy source of life. – Breakdown of sugar (catabolism) different ways: •Aerobic respiration •Anaerobic respiration •Fermentation Energy Generating Patterns
- 20. Aerobic respiration – Most efficient way to extract energy from glucose. – Process: Glycolysis Kreb Cycle Electron transport chain – Glycolysis : Several glycolytic pathways – The most common one: glucose-----> pyruvic acid + 2 NADH + 2ATP
- 21. General Outline of Aerobic Respiration Glycolysis Krebs Cycle Electron Transport System Transition Reaction
- 22. General Outline Glucose Pyruvic Acid Glycolysis Oxygen Aerobic No Oxygen Anaerobic Transition Reaction Krebs Cycle ETS 36 ATP Fermentation
- 23. Glycolysis Steps – A fuel molecule is energized, using ATP. 1 3 1 Glucose Step 2 3 4 Glucose-6-phosphate Fructose-6-phosphate Glyceraldehyde-3-phosphate (G3P) Step A six-carbon intermediate splits into two three-carbon intermediates. 4 Step A redox reaction generates NADH. 5 5 1,3-Diphosphoglyceric acid (2 molecules) 6 Steps – ATP and pyruvic acid are produced. 6 9 3-Phosphoglyceric acid (2 molecules)7 2-Phosphoglyceric acid (2 molecules)8 2-Phosphoglyceric acid (2 molecules) 9 (2 molecules per glucose molecule) Pyruvic acid Fructose-1,6-diphosphate Energy In: 2 ATP Energy Out: 4 ATP NET 2 ATP
- 24. How Glycolysis Works Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
- 25. Krebs Cycle
- 26. Electron Transport Chain • Groups of redox proteins – On inner mitochondrial membrane – Binding sites for NADH and FADH2 • On matrix side of membrane • Electrons transferred to redox proteins • NADH reoxidized to NAD+ • FADH2 reoxidized to FAD
- 27. ETC
- 28. Generation of a proton-motive force(1)
- 29. Generation of a proton-motive force(2)
- 31. Electron Transport System and ATP Synthesis Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.
- 32. Anaerobic respiration – Final electron acceptor : never be O2 Sulfate reducer: final electron acceptor is sodium sulfate (Na2 SO4) Methane reducer: final electron acceptor is CO2 Nitrate reducer : final electron acceptor is sodium nitrate (NaNO3) O2/H2O coupling is the most oxidizing, more energy in aerobic respiration. Therefore, anaerobic is less energy efficient.
- 33. Fermentation (F) Glycosis: Glucose ----->2 Pyruvate (P.A)+ 2ATP + 2NADH Fermentation pathways a. Homolactic acid F. P.A -----> Lactic Acid eg. Streptococci, Lactobacilli b. Alcoholic F. P.A -----> Ethyl alcohol eg. yeast
- 34. Fermentation – An overview
- 36. c. Mixed acid fermentation P.A -----> lactic acid acetic acid H2 + CO2 succinic acid ethyl alcohol eg. E.coli and some Enterobacter d. Butylene-glycol F. P.A -----> 2,3, butylene glycol eg. Pseudomonas e. Propionic acid F. P.A -----> 2 propionic acid eg. Propionibacterium
- 37. 37 Metabolic strategies Pathways involved Final e- acceptor ATP yield Aerobic respiration Glycolysis, TCA, ET O2 38 Anaerobic respiration Glycolysis, TCA, ET NO3 -, SO4 -2, CO3 -3 variable Fermentat ion Glycolysis Organic molecules 2
- 38. Energy/carbon classes of organisms
- 39. Comparison of reaction centers of anoxyphototrophs
- 40. Photosynthesis • Overview of Photosynthesis – Light-dependent Reactions: • Light energy is harvested by photosynthetic pigments and transferred to special reaction center (photosystem) chlorophyll molecules. • The light energy is used to strip electrons from an electron donor (the electron donor goes from a reduced to an oxidized state). • The electrons are shuttled through a series of electron carriers from high energy state to a low energy state. • During this process, ATP is formed. • In the cyclic pathway of electron transport, electrons are returned to the electron transport chain • In the noncyclic pathway, the electrons are used to reduce NAD (or NADP) to NADH (or NADPH)
- 41. Photosynthesis Light-independent Reactions: • ATP and NADH (NADPH) from the light- dependent reactions are used to reduce CO2 to form organic carbon compounds (carbon fixation). • The reduced organic carbon is usually converted into glucose or other carbohydrates.
- 42. Photosynthesis Oxygenic photosynthesis – Found in cyanobacteria (blue-green algae) and eukaryotic chloroplasts – Electron donor is H2O: Oxidized to form O2 – Two photosystems: PSII and PSI – Major function is to produce NADPH and ATP for the carbon fixation pathways
- 44. Photosynthesis Anoxygenic photosynthesis – Found in: • Green sulfur bacteria (e.g. Chlorobium) • Green nonsulfur bacteria (e.g. Chloroflexus) • Purple sulfur bacteria (e.g. Chromatium) • Purple nonsulfur bacteria (e.g. Rhodobacter)
- 45. Photosynthesis Anoxygenic photosynthesis (cont.) b) Electron donors vary: • H2S or So in the green and purple sulfur bacteria • H2 or organic compounds in the green and purple nonsulfur bacteria c) Only one photosystem • In green bacteria, the photosystem is similar to PSI • In purple bacteria, the photosystem is similar to PSII d) Primary function is ATP production, chiefly via cyclic photophosphorylation
- 46. Photosynthetic bacteria (1) Chlorobium-green sulfur bacteria Use green pigment chlorophyll Use H2S (hydrogen sulfide), S (sulfur), Na2S2O3 (sodium thiosulfate) and H2 as e- donors. (2) Chromatium-purple sulfur bacteria Use purple carotenoid pigment, same e-donors (3) Rhodospirillum-non sulfur purple bacteria Use H2 and other organic compounds such as isopropanol etc, as e-donors. Reaction: CO2 + 2H2A -----> CH20 + H20 +2A • A is not O
- 47. Chemolithotrophy • Features of Chemolithotrophy – Electrons are removed from a reduced inorganic electron donor – The electrons are passed through a membrane- bound electron transport pathway, often coupled to the synthesis of ATP and NADH – The electrons are ultimately passed to a final electron acceptor – ATP and NADH may be used to convert CO2 to carbohydrate
- 48. Chemolithotrophy Examples of electron donors – Ammonia (NH4 +) Nitrite (NO2 -) in Nitrosomonas – Nitrite (NO2 -) Nitrate (NO3 2-) in Nitrobacter – Hydrogen sulfide (H2S) Sulfur (So) in Thiobacillus and Beggiatoa – Sulfur (So) Sulfate (SO4 2-) in Thiobacillus – Hydrogen (H2) Water (H2O) in Alcaligenes
- 49. Chemolithotrophy Examples of electron acceptors – Oxygen (O2) Water (H2O) in many organisms – Carbon dioxide (CO2) Methane (CH4) in the methanogenic bacteria
- 50. Chlorophyll a and bacteriochlophyll a
- 51. Chemoautotroph – Some bacteria use O2 in the air to oxidize inorganic compounds and produce ATP (energy). The energy is enough to convert CO2 into organic material needed for cell growth. – Examples: Thiobacillus (sulfur S) Nitrosomonas (ammonia) Nitrobacter (nitrite) – Various genera (hydrogen etc.)