Bio-electricity

Bio-electricity

Development, Architecture, and Generation of Bio-electricity :



Origin of Life - The Earth started to solidify in a whole piece about 4.5 billion years ago. Starting from life-less organic molecules, life in the form of microbes emerged about one billion years later. It is conceivable that proteins and nucleic acids can assemble themselves in shallow ponds. The complex assembly that made the transition to life would require a closed environment to proceed efficiently and to keep the end product from leaking out. There are some macromolecules such as phospholipid, which can naturally form a tiny sphere bound by a membrane in water (the droplet is called liposome). Various substances can be incorporated into the droplet until the right mixture is acquired to start up metabolism and reproduction.

Figure 05 Origin of Life [view large image]

• Cell Membrane - The modern cell membrane consists of two layers of amphipathic phospholipids which spontaneously

  arrange so that the hydrophobic "tail" regions are isolated from the surrounding polar fluid, causing the more hydrophilic "head" regions to associate with the intracellular and extracellular fluid (Figure 06). Such arrangement is essential because most of the life supporting materials (and waste) are solvable in water. The pores (with a size of ~ 10-6 cm) occupy about 50% of the surface, and are inserted on the membrane in order to facilitate the absorption (of nutrient) and removal (of waste). Since the membrane has the consistency of machine oil, the pores tend to float about and must be anchored by cytoskeletion.

  Figure 06 Cell Membrane [view large image]

  Pores that process passive transport letting substance in and out through concentration gradient are called channels, while those use energy in active transport to move the substance against its concentration gradient are called pump. This is one of the indicators to show the non-equilibrium nature of life (see also "carbon compounds").

  		The production of ATP is another example of bio-electricity at work. It relies on the proton (H+) pump to establish a concentration gradient (or electrical potential). This pump obtains its energy by the redox gradient which extracts energy from the electron as it move down the redox energy scale. A positive electric potential is built up as the proton (H+P) concentration increases in the intermembrane space. Consequently protons move down the gradient through a pore called ATP synthase, which converts ADP to ATP by adding one more phosphate into the structure (see
  Figure 07 ATP Synthase [view large image]	Figure 08 Mitochondria	Figure 07, also see an animation on the synthesis of the ATP from individual ADP and Pi to an intermediate stage of ADP-P in the F1 domain - a view from the top). Energy is infused into ATP in the process. This is a

  very good example to show the conversion of the energy to different forms from chemical to electrical to mechanical and finally back to chemical. Anyway, the ATP finally exits the mitochondria from another pore (Figure 08).
  
  The ATPs sustain most of the energy requirement within the cells in most organisms on Earth. It is used for synthetic reactions, active transport, nervous conduction, and muscle contraction. A speific example is the operation of the sodium pump, which would not work without the presence of ATP (see Figure 06).
  
  The chain of respiration process starts with glucose and oxygen entering the mitochondria (Figure 08). Two sub-pathways in the intermediate stage separate the glucose C₆H₁₂O₆ into CO₂ and H. The hydrogen is broken down further into H⁺ and e^-. The electron goes through a transport chain to pump out the H⁺, which in turn re-enter via the ATP synthase to generate the ATP (with ~ 0.32 ev/ATP stored in the extra phosphate link). Eventually, the H⁺ and e^- combines with O₂ to produce water to complete the process, which can be summarized in chemical formula as : C₆H₁₂O₆ + 6O₂ 6CO₂ + 6H₂O + energy.
  
  See more about ATP in "ATP - Energy Supplier for Life (2020 Edition)".
  
  

  		Cellular Fluids - All Modern cells have higher concentration of potassium ion K+ in the intracellular fluid. Since life started from the sea and the sea contains lot of sodium ion Na+, it is not clear what made the preference for K+ ions inside the cell. One scenario suggests that the proto-cell evolved in a "warm little pond" (Figure 09), in which organic molecules could be concentrated. Potassium ions leached from the surrounding rocks or clays are subsequently incorporated into the cell.
  Figure 09 Birthplace of Proto-cell	Figure 10 Cellular Fluids

  The extracellular fluid in unicellular Organisms and lower animals is essentially the sea or a coating of wet water, which would contain food, oxygen, hormones, ions, plus other chemicals necessary for life and they all mixed together with wastes. Interstitial fluid (ISF) begins to appear in roundworm. Blood vessels are established only at the level of earthworm and up as illustrated in Figure 10 (also see "Three Germ Layers").




Triggering Mechanism - Among other substances in the body fluid, it is the sodium and potassium ions that's responsible for the generation of bio-electricity. At the resting state the Na+ concentration is higher outside the cell, and the K+ concentration becomes dominant inside. Usually, the sodium and potassium channels and pumps are closed. However there is a small leakage of K+ ions from the potassium channels resulting in electric charge in-balance with a voltage of about -70 mv inside the membrane. The channels are open by the binding of chemicals, mechanical stress (resulting in conformal change), or change in voltage at the membrane. Figure 11 shows the conformal change of the retinal molecule (induced by the illumination of visible light), which generates an electrical impulse for seeing. Hearing and touching involve mechanical stress, while smell and taste are the results of the binding of chemicals. The sodium pump is open by detecting the change in ionic concentration.

Figure 11 Conformal Change of Retinal

See the "Five Senses".

		Nerve Impulse - The basic units of bio-electrical conduction are the axons and dendrites projecting out from the neuron call (Figure 12). These units are bundled together to form the nerve, which is hidden inside the body for protection, only the sensors are located on the surface (see more in "Neurons and Nerves"). Figure 13 shows the sequence of events that generates an electrical impulse, the insert portrays the action potential at a point X as a function of time :
Figure 12 Neuron [view large image]	Figure 13 Nerve Impulse

(A) - At resting state the -70 mv inside the axon is maintained by K⁺ ion leakage.
(B) - A triggering action opens the sodium channel. The inflow of Na⁺ ions raises the voltage to +50 mv - the peak of the "action potential".
(C) - The potassium channel opens to let the K⁺ ions out dropping the voltage back to -70 mv.
(D) - The change in voltage induces the next sodium channel to open repeating the sequence so that the electrical impulse

moves along down stream to the synapse (the terminal), where the release of neurotransmitters passes the impulse to the dendrite of another neuron cell. The sodium pump re-establish the resting condition up stream by moving K+ ions in and Na+ ions out. The sequence of synaptic action after the arrival of nerve impulse starts with the opening of ion channels, which allow calcium ions to rush in (see Figure 14). This is one more example of bio-electricity in action. Since proper calcium ion concentration is vital for a host of functions within the cell (such as : triggering a fertilized egg to develop, skeletal muscle cells to contract, secretion by secretory cells, ... etc.), there are calcium pumps to maintain low concentration of free Ca2+ in the cytosol.

Figure 14 Synapse [view large image]

See more in "Neurotransmitters".

Notes :
1. Neurotransmitter comes in many types (see Types of Neurotransmitter). However, it is not the only chemical messenger employed by organisms to communicate. There are hormones transmit long-range signals to initiate action in other cells; pheromones to act (by diffusion in the air) as sexual attractants, territorial markers and alarm bells.
2. Electrical synapse transmits nerve impulse by direct contact. It is about ten times faster and is used for quick response.

Table 01 Comparison of Conventional and Bio-Electricity

Table 02 Bio-electricity in Action

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