Transduction (biophysics)
Encyclopedia
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.
Photonic energy, the kinetic energy
of a photon
, may follow the following paths:
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 is quite wrong: NADP is reduced (electrons are added) to NADPH in the light reactions of linear electron transport. No ATP involved directly. Phosphate is "linked" to ADP, forming ATP, but this does not involve NADP(H), it involves the proton gradient (and ATP synthase) generated by photosynthetic electron transport processes.] 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 (cytochrome
s), 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.
Biophysics
Biophysics is an interdisciplinary science that uses the methods of physical science to study biological systems. Studies included under the branches of biophysics span all levels of biological organization, from the molecular scale to whole organisms and ecosystems...
, transduction is the conveyance of energy from one electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
(a donor) to another (a receptor), at the same time that the class of energy changes.
Photonic energy, the kinetic energy
Kinetic energy
The kinetic energy of an object is the energy which it possesses due to its motion.It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes...
of a photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
, 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
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
, when the electrons of the "chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
pair" receive the photon energy from the "collecting" associated pigments, the photonic energy is "destined" to link one molecule of phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
to one of NAD
Nicotinamide adenine dinucleotide
Nicotinamide adenine dinucleotide, abbreviated NAD, is a coenzyme found in all living cells. The compound is a dinucleotide, since it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine base and the other nicotinamide.In metabolism, NAD is involved...
. The resulting NADP in turn will use the stored energy in the generation of ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, which is the end point of the light-induced photosynthetic process. [This is quite wrong: NADP is reduced (electrons are added) to NADPH in the light reactions of linear electron transport. No ATP involved directly. Phosphate is "linked" to ADP, forming ATP, but this does not involve NADP(H), it involves the proton gradient (and ATP synthase) generated by photosynthetic electron transport processes.] 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 (cytochrome
Cytochrome
Cytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as monomeric proteins or as subunits of bigger enzymatic complexes that catalyze redox reactions....
s), in a downward way so that energy is partially dissipated at each step. The liberated heat energy serves the homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
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.
See also
- HomeostasisHomeostasisHomeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
- PhotosynthesisPhotosynthesisPhotosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
- ChlorophyllChlorophyllChlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
- PhosphatePhosphateA phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
- Pigments
- NADNicotinamide adenine dinucleotideNicotinamide adenine dinucleotide, abbreviated NAD, is a coenzyme found in all living cells. The compound is a dinucleotide, since it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an adenine base and the other nicotinamide.In metabolism, NAD is involved...
- ATPAdenosine triphosphateAdenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
- CytochromeCytochromeCytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as monomeric proteins or as subunits of bigger enzymatic complexes that catalyze redox reactions....