Respiration

Respiration in microorganism

1. RESPIRATION PRAGYA TYAGI MICROBIOLOGY

2. RESPIRATION Respiration is the process through which the energy stored in fuel is converted into a form that a cell can use. Typically, energy stored in the molecular bonds of a sugar or fat molecule is used to make ATP, by taking electrons from the fuel molecule and using them to power an electron transport chain. Respiration is crucial to a cell’s survival because if it cannot liberate energy from fuel to drive its life functions, the cell will die.

3. Aerobic respiration---- Plants and animals transport glucose and oxygen to tiny structures in their cells, called mitochondria. Here, the glucose and oxygen take part in a chemical reaction. The reaction is called aerobic respiration, and it produces energy which transfers to the cells. Aerobic respiration makes two waste products: carbon-dioxide and water. Animals remove carbon dioxide from their bodies when they breathe out. In daytime, plants use some of this carbon dioxide for photosynthesis. At night, they release the carbon dioxide to their surroundings.

4. AEROBIC RESPIRATION Aerobic Respiration is the process by which the energy from glucose is released in the presence of oxygen. It takes place only if oxygen is available. For instance, if glucose were oxidized, the result would be energy, carbon dioxide and water. Take a look at the chemical formula given below.              C6H12O6 + 6O2 = 6CO2 + 6H2O + Energy (ATP) In simple words,               Glucose + Oxygen = Carbon-dioxide + Water + Energy (ATP) In brief, aerobic respiration helps in release of maximum energy and also gets rid of carbon-dioxide and excess water. The four stages involved in the aerobic respiration process are 1. Glycolysis (or EMP-Pathway of Glycolytic Breakdown) 2. Pyruvate Oxidation or Conversion of Pyruvic Acid to Acetyl Coenzyme A 3. TCA Cycle or Krebs Cycle 4 . Terminal Oxidation

5. Aerobic respiration uses oxygen to break down glucose, amino acids and fatty acids and is the main way the body generates adenosine triphosphate (ATP), which supplies energy to the muscles. After glycolysis (the anaerobic breakdown of glucose into pyruvate, pyruvate is converted to acetyl CoA in the matrix of the energy-transferring mitochondria, via the link reaction. Next is the Krebs cycle, which occurs twice per glucose molecule, producing – among other chemicals that feed into the aerobic part of the process – more ATP. Aerobic Respiration is the process by which the energy from glucose is released in the presence of oxygen. It takes place only if oxygen is available. Although glycolysis occurs in all organisms except primitive bacteria,

6. Anaerobic respiration Anaerobic respiration is a form of respiration that is contrasted with aerobic respiration in that it does not use oxygen. It is an alternative method of respiration that is used when oxygen is not present and derives energy from other chemicals nearby or within the body. Aerobic respiration produces more energy and is 15 times more efficient than anaerobic respiration. This is why most large creatures breathe to take in oxygen. Instead of oxygen, anaerobic cells use substances such as sulfate, nitrate, sulfur, and fumarate to drive their cellular respiration.

7. ANAEROBIC RESPIRATION Anaerobic respiration is an alternate mode of energy generation in which an exogenous electron acceptor other than O2 is used in electron transport chain leading to a proton motive force. In contrast to aerobic respiration where O2 is used as electron acceptor, the electron acceptors used in anaerobic respiration include nitrate, sulphate, carbonate, ferric ion and even certain organic compounds (for example, fumarate, chlorate, trimethylamine oxide, etc.) The use of these alternate electron acceptors allows microorganisms to respire in environments where oxygen is absent. Because the solubility of oxygen in water is rather low, and because oxygen is in such high demand as an electron acceptor by aerobic organisms, anaerobic respirations are thus ecologically extremely important for anaerobic organisms, the prokaryotes. Anaerobic respiration, therefore, is a hallmark of prokaryotes and is rare in eukaryotes

8. Anaerobic Respiration: A Molecule other than Oxygen is used as the Terminal Electron Acceptor in Anaerobic Respiration

9. Anaerobic respiration is the formation of ATP without oxygen. This method still incorporates the    respiratory electron transport chain, but without using oxygen as the terminal electron acceptor.  Instead, molecules such as sulfate (SO42-), nitrate(NO3–), or sulfur (S) are used as electron acceptors. These molecules have a lower reduction potential than oxygen; thus, less energy is formed per molecule of glucose in anaerobic versus aerobic conditions. Many different types of electron acceptors may be used for anaerobic respiration. Denitrification is the utilization of nitrate (NO3-) as the terminal electron acceptor. Nitrate, like oxygen, has a high reduction potential. This process is widespread, and used by many members of Proteobacteria.  Many denitrifying bacteria can also use ferric iron (Fe3+) and different organic electron acceptors.        Sulfate reduction uses sulfate (SO2-4) as the electron acceptor, producing hydrogen sulfide        (H2S)  as a metabolic end product. Sulfate reduction is a relatively energetically poor process,        and  is used by many Gram-negative bacteria found within the δ-Proteobacteria. It is also used in           Gram-positive organisms related to Desulfotomaculum or the archaeon Archaeoglobus .

10. Oxygen toxicity Low or undetectable levels of superoxide dismutase and catalase allow oxygen radicals to form in anaerobic bacteria and to inactivate other bacterial enzyme systems. The broad classification of bacteria as anaerobic, aerobic, or facultative is based on the types of reactions they employ to generate energy for growth and other activities. In their metabolism of energy-containing compounds, aerobes require molecular oxygen as a terminal electron acceptor and cannot grow in its absence. Anaerobes, on the other hand, cannot grow in the presence of oxygen. Oxygen is toxic for them, and they must therefore depend on other substances as electron acceptors. Their metabolism frequently is a fermentative type in which they reduce available organic compounds to various end products such as organic acids and alcohols. The facultative organisms are the most versatile. They preferentially utilize oxygen as a terminal electron acceptor, but also can metabolize in the absence of oxygen by reducing other compounds. Much more usable energy, in the form of high-energy phosphate, is obtained when a molecule of glucose is completely catabolized to carbon dioxide and water in the presence of oxygen (38 molecules of ATP) than when it is only partially catabolized by a fermentative process in the absence of oxygen (2 molecules of ATP). The ability to utilize oxygen as a terminal electron acceptor provides organisms with an extremely efficient mechanism for generating energy.

11. Several studies indicate that aerobes can survive in the presence of oxygen only by virtue of an elaborate system of defenses. Without these defenses, key enzyme systems in the organisms fail to function and the organisms die. Obligate anaerobes, which live only in the absence of oxygen, do not possess the defenses that make aerobic life possible and therefore cannot survive in air. During growth and metabolism, oxygen reduction products are generated within microorganisms and secreted into the surrounding medium. The superoxide anion, one oxygen reduction product, is produced by univalent reduction of oxygen:                                                    O2e- → O2– It is generated during the interaction of molecular oxygen with various cellular constituents, including reduced flavins, flavoproteins, quinones, thiols, and iron-sulfur proteins. The exact process by which it causes intracellular damage is not known; however, it is capable of participating in a number of destructive reactions potentially lethal to the cell. Moreover, products of secondary reactions may amplify toxicity. For example, one hypothesis holds that the superoxide anion reacts with hydrogen peroxide in the cell:                               O 2 –  + H 2 O 2  → OH –  + OH .  + O 2

12. This reaction, known as the Haber-Weiss reaction , generates a free hydroxyl radical (OH·), which is the most potent biologic oxidant known. It can attack virtually any organic substance in the cell. A subsequent reaction between the superoxide anion and the hydroxyl radical produces singlet oxygen (O2* ), which is also damaging to the cell:                                               O2– + OH → OH + O2* The excited singlet oxygen molecule is very reactive. Therefore, superoxide must be removed for the cells to survive in the presence of oxygen. Most facultative and aerobic organisms contain a high concentration of an enzyme called superoxide dismutase. This enzyme converts the superoxide anion into ground-state oxygen and hydrogen peroxide, thus ridding the cell of destructive superoxide anions:                                   2O2– + 2H+ Superoxide Dismutase  O2 + H2 O2

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