Question

How the ETC works. What is some evidence that supports the ETC? What is a proton pump? A baby on a cold day was left in a cold house with no heat. The adults in the house froze to death but the baby lived. Using the ETC, how can you explain this situation?

Answer 1

• during the process of glycolysis and citric acid cycle , most of the free energy is released which is captured by two co enzymes in its reduced form NADH and FADH2. during electron transport system , the electrons eventually transpoted from NADH and FADH2 to oxygen molecule and water molecule is formed.
• the free energy released during oxidation of NADH and FADH2 molecules by oxygen is sufficient to drive the synthesis of several molecule of ATP from ADP and Pi,
• there is a chain of transporter electron protein in theinner  mitochondrial membrane , which carries step by step electrons .
• during electron transport from NADH to O2, protons from the mitochondrial matrix are transported uphill across the inner mitochondrial membrane to inter membrane space and a proton concentration gradient forms across it .
• one thing we should remember that the outer membrane of mitochondria is highly permeable to proton , so protons moves through it in a fast rate, therefore the concentration of proton is lower in mitochondrial matrix than intermitochondrial matrix and cytosol of cell.
• in short if we focus on the both side of inner mitocondrial membrane , on inner side of it matrix is present and on outer side intermembrane space is present [a space between inner and outer mitochondrial membrane].
• a constant up hilling of protons is going through the inner membrane which results in an electrical potential .
• this means that on the inner [matrix] side of inner membrane there are negative chrge ions [pH high ]and on outer side[intermembrane space ]  there are more positive ions ie protons [Low pH].
• this proton gradiation across the membrane is collectively called proton motive pump. to maintain the equilibrium , an Enzyme ATP synthase also called F0- F1 partical helps to move back proton into matrix . A force is created during the passing of each proton through it which helpful for the formation of ATP from ADP and Pi.
• more the number of mitochondria more the production of ATP and generation of heat.
• let us see the number of mitochondria in white fat tissues and brown fat tissues.
• Brown-fat tissue, whose color is due to the presence of abundant mitochondria,is specialized for the generation of heat. In contrast, white-fat tissue is specialized for the storage of fat and contains relatively few mitochondria.

• •In the inner membrane of brown-fat mitochondria, inner-membrane thermogenin [protein] functions as a natural uncoupler of oxidative phosphorylation. Thermogenin does not form a proton channel like the F0 complex and typical channel proteins. Rather, thermogenin is a proton transporter whose amino acid sequence is similar to that of the mitochondrial ATP/ADP antiporter , it functions at a rate that is characteristic of transporters, but is 1-million-fold slower than typical channel proteins .Like other uncouplers, thermogenin dissipates the proton-motive force across the inner mitochondrial membrane, converting energy released by NADH oxidation to heat.

  •The amount of thermogenin is regulated depending on environmental conditions. For instance, during the adaptation to cold, the ability of tissues to generate heat (thermogenesis) is increased by the induction of thermogenin synthesis. [may constitute up 15 percent ]

  •Adult humans have little brown fat, but human infants have a great deal. In the newborn, thermogenesis by brown-fat mitochondria is vital to survival, as it also is in hibernating mammals. In fur seals and other animals naturally acclimated to the cold, muscle-cell mitochondria contain thermogenin; as a result, much of the proton-motive force is used for generating heat, thereby maintaining body temperature.

• therefore adult frozen faster than baby .