Transduction (biophysics)
In biophysics, transduction is the conveyance of energy from one electron (a donor) to another (a receptor), at the same time that the class of energy changes.
Photosynthesis
Photonic energy, the kinetic energy of a photon, may follow the following paths:
- be released again as a photon of less energy;
- be transferred to a recipient with no change in class;
- be dissipated as heat; or
- be transduced
In photosynthesis, when the electrons of the "chlorophyll pair" receive the photon energy from the "collecting" associated pigments, the photonic energy is "destined" to link one molecule of phosphate to one of NAD. The resulting NADP in turn will use the stored energy in the generation of ATP, which is the end point of the light-induced photosynthetic process. This means that the photon's energy ends up its circuit by being transduced to an electron that takes part in the formation of a molecular link of energy-rich phosphate.
In the pathway of this end-point transduction, the energy is transferred along a number of molecules (cytochromes), in a downward way so that energy is partially dissipated at each step. The liberated heat energy serves the homeostasis of the plant, and at the end of the chain the remaining energy is perhaps exactly the one that is needed to build NADP.
This process is committed; i.e. there is no return path. Homeostasis, theoretically, might save the day only at the beginning: before the luminic energy transferred to the "chlorophyl pair" is conveyed to the first element of the cytochrome chain, there is a gap in the process when the energy is carried as a series of excitons. These are now called resonant-energy-transferring molecules of the chlorophyll class, which transfer what is considered electromagnetic energy, from one to its neighbor with no participation of electrons nor enzymes. At this stage, if the first pigment has received an excess of light, the "exciton" perhaps might dissipate the energy as heat.
Signal transduction
In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes and linked through second messengers resulting in what is thought of as a "second messenger pathway".
Many, if not all, of the signal conversions may convey or use energy from one electron (a donor) to another (a receptor), while the form of energy remains unchanged or usually does not change. Energy consumption occurs. But the pathway may not always be committed or leading.
A signal transduction is usually rapid, lasting on the order of milliseconds in the case of ion flux, to minutes for the activation of protein and lipid mediated kinase cascades. In many signal transduction processes, the number of proteins and other molecules participating in these events increases as the process eminates from the initial stimulus, resulting in a "signal cascade". Often a relatively small stimulus elicits a large response.
Signal transductions can occur in many directions. Some occur along the cytoplasmic surface of the cell membrane, like the epinephrin pathway.
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Others occur inwardly, such as the MAPK/ERK pathway, ultimately arriving inside the cell nucleus.
If a possible set of proteins for the MAPK/ERK pathway of signal transduction were linked together physically without the proteins being unfolded, there connected length as suggested in the table below would only be ~37 nm in length from the cytoplasmic side of the cell membrane to the cytoplasmic side of the nuclear envelope. For a typical cell of diameter 10 µm, with a nucleus of about 5 µm in diameter, just under 5000 nm remain for the signal transduction to occur across.
| Protein | Mass (Da) | Likely size (nm) | Connected length (nm) |
|---|---|---|---|
| GRB2 | 25k | ~3 | ~3 |
| SOS1 | 152k | ~6.5 | ~9.5 |
| RASD1 | 32k | ~4 | ~13.5 |
| RAF1 | 73k | ~5 | ~18.5 |
| MAP3K | 164k | ~6.5 | ~25 |
| MKNK1 | 30k | ~4 | ~29 |
| CREB1 | 25k | ~3 | ~32 |
| RPS6KA11 | 81k | ~5 | ~37 |
Physiological transduction
In physiology, transduction is the conversion of a stimulus from one form to another.
Transduction in the nervous system typically refers to synaptic events wherein an electrical signal, known as an action potential, is converted into a chemical one via the release of neurotransmitters. Conversely, in sensory transduction a chemical or physical stimulus is transduced by sensory receptors into an electrical signal. Each of these probably involves a loss of energy.
Genetic transduction
Genetic transduction is the process by which bacterial DNA is moved from one bacterium to another usually by a virus.
While the form of energy probably does not change, energy is lost and conveyed.
Acknowledgements
The content on this page was first contributed by: Henry A. Hoff.
Initial content for this page in some instances came from Wikipedia.