William Schroll
April 10, 2008
Agroecology
Electron Transport Chain
(ETC)
Electron transport chain is an oxidative reaction that affects the transfer of electrons through a series of carriers. This also is called the respiratory electron chain, which is the final stage of aerobic respiration. Electron transport in addition can occur in a phototrophic organism this process is called Photophosphorylation, which forms ATP (adenosine triphosphate) from ADP (adenosine diphosphate) using light energy from photosynthesis. ("Electron Transport Chain " 198,458) This also happens in a chemotropic organism but instead of light to convert energy, it uses oxygen instead. ETC in chemotrophic organisms occurs in the mitochondria with NADH (nicotinamide adenine dinucleotide hydride) or FADH2 (flavin adenine dinucleotide hydrate) created by the Krebs cycle which transfers electrons through carrier molecules. Initially NADH enters Complex I and is converted into NAD+. Carriers in complex II, III, and VI and coupled together which are called cytochromes that undergoes reverse reduction-oxidation reaction accepting electrons Then donating them to the next carrier in the chain, this is called electron flow. (Coupling is an event of more than one reaction where one event normally cannot occur without the other.) Then during the electron flow, it combines electrons and hydrogen ions to oxygen (O2) to form water (H2O) this helps from ATP to create glucose and energy. This creates energy into ATP by enzymes called ATP syntheses, which contains a similar genetic code in all living organisms on planet Earth. (Campbell and Reece 155-173) Without electron transport, the human body could not process extra glucose stored in the body for later energy use.
Simple Aerobic Example
Fuel must be burned slowly to create a steady flow of energy. This must happen is small steps because if it occurs in one large moment the energy omitted cannot be harnessed efficiently. The oxidation of methane by oxygen is a good example. This reaction happens when methane is burned out of a cooking stove, this is also a good example in a combustion engine in an automobile which the energy released move the piston which propel the car. An organic example of electron transport, aerobic respiration must be present for oxidative phosphorylation to occur, converting glucose into oxygen and water. This will be an energy-yielding reduction/oxidation process with a fuel like glucose.
C6H12O6 + 6O2 → 6O2 +6H20
The glucose will oxidize into the six oxygen (O2) atoms and the six oxygen atoms from the first equation will be reduced into six water molecules. When the glucose is oxidized, oxygen is reduced or gets smaller and the electrons that are presents lose energy in the process. Because organic molecules have large amounts of hydrogen they are, good fuel sources, they can be easily bonded with electrons and can form oxygen (O2) molecules.(Horton and Moran 429-456) The equation above show that in the presence of oxygen the hydrogen forms glucose and is transfers into oxygen and water. This equation does not show the transfer of electrons that will convert the hydrogen into oxygen, which then will create energy. By the oxidation of glucose molecules, respiration takes energy out of storage molecules to make it available for ATP synthesis. Carbohydrates and fats are the main source of energy for chemotrophs; these two hold abundant amounts of electrons for electron transport because of their large amounts of hydrogen. Without the barrier of activation energy, there would be a huge amount of electrons expelled, too many to be efficiently harnessed and the organism would loss energy. If these barriers were not present C6H12O6 combine with oxygen (O2) simultaneously, which if ignited would release 686 kcal per molecule of glucose but the human body cannot get hot enough to create ignition so the energy would be lost. Even if a person ate pure sugar, the body would lower the barriers to the food and would store most of the glucose for later use while still oxidizing slowly. (Campbell and Reece 155-173)
Photophosphorylation
Photosynthesis is the conversion of light energy into chemical energy. Light energy is absorbed by the chlorophyll and drives the transfer of electrons and hydrogen from water in the plant to the acceptors; NADP+ (nicotinamide adenine dinucleotide phosphate) the electrons are stored here temporally. The water (H20) is split in to hydrogen and oxygen; this is why O2 is a byproduct of photosynthesis. NADP+ acts as an electron carrier, which in the presents of light NADP+ is combined with two electrons to form NADPH. In the presence of light, it also creates ATP by powering the additional ADP, which is called Photophosphorylation. Thus, light energy is converted into two types of chemical energy, NADPH, a source of energized electrons and ATP. The second process of photosynthesis is the Calvin cycle; it converts fixed carbon into carbohydrates by adding electrons. This is done with the electrons from the NADPH. This means that the only way the Calvin cycle can create glucose is with NADPH and ATP, which in most plant light needs to be present to make these two molecules to reduce CO2 into sugar. NADP+ and ADP will hit the cell membrane and pick up extra electrons to help is this conversion process. The main difference between oxidative phosphorylation and photophosphorylation is that one happens in the mitochondria and the other happens in the chloroplast. (Campbell and Reece 155-173)
Bibliography
Campbell, Neil , and Jane Reece. Biology. 6th . New York new York : Benjamin Cumming , 2002.
Horton , Robert , and Laurence Moran, Raymond Ochs David Rawn Gray Scrimgour . Biochemistry . 3rd .
Upper Saddle River, NJ: Prentice Hall , 2002.
“Electron Transport Chain, Photophosphorylation.”Oxford Dictionary of Biology . 4th ed . 2000.