Visible light causes isometric (atom arrangement) changes in opsin protein molecules in the cones of the eye. Opsin itself does not absorb visible light, but when it is bonded with 11-cis-retinal to form rhodopsin, it then has a broad absorption band in the visible region of the spectrum, with a peak around 500 nm. Upon absorption of a photon of light in the visible range, cis-retinal can isomerize (change atom arrangement) to all-trans-retinal. This isomerization has several consequences:
1. Conformational changes in opsin: The isomerization of retinal affects the shape of the opsin molecule, which consists of 348 amino acids. The molecule changes from an overall bent structure to one that is more or less linear, resulting in trigonal planar bonding (120° bond angles) about the double bonds.
2. Activation of the G protein: The conformational changes in opsin lead to the activation of the G protein, which mediates an enzymatic cascade that signals the detection of the photon.
3. Signal transduction: The visual cycle, a sequence of biochemical reactions, occurs via G-protein coupled receptors called retinylidene proteins. The absorption of light by the chromophore allows the fast cis–trans isomerization to proceed, followed by slower conformational changes in opsin on the millisecond scale.
4. Hyperpolarization of the photoreceptor cell: The light absorption-induced isomerization of retinal from 11-cis to all-trans triggers a signaling cascade that leads to the hyperpolarization of the photoreceptor cell. This process is essential for vision in both rod and cone photoreceptors.
These processes, photochemical changes involving the protein opsin and the cis/trans isomers of retinal, are crucial for the visual system to detect and process light signals.
What is Isomerization?
Isomerization is a chemical process in which a molecule, polyatomic ion, or molecular fragment is transformed into an isomer with a different chemical structure or configuration, but with the same chemical composition. Isomerization can result in a shape change if the isomer has a different spatial arrangement of atoms. However, isomerization can also occur without resulting in a shape change if the isomers have the same spatial arrangement of atoms but differ in the position of functional groups or double bonds. For example, the isomerization of butane to isobutane involves a rearrangement of the carbon skeleton without changing the spatial arrangement of atoms, resulting in a branched isomer with different physical and chemical properties.
Are Opsin Isomerizations Significant Chemical Changes?
Yes, opsin isomerizations involve significant chemical changes. When 11-cis-retinal absorbs a photon of light and isomerizes to all-trans-retinal, it causes a change in the shape of the opsin molecule, leading to the activation of the opsin and the initiation of a cascade of biochemical reactions, ultimately resulting in changes in charge and the generation of an electrical impulse. This process is crucial for vision and is a fundamental step in the visual transduction cascade. The functional diversity of opsins and their ability to sense light of different wavelengths or colors demonstrate the importance of these isomerizations in enabling organisms to adapt to their environments. Therefore, opsin isomerizations are indeed significant chemical changes with important implications for vision and the adaptation of organisms to different light conditions.
How do Photons of Visible Light Cause Isomerization?
Photons of visible light cause the isomerization of opsins through a process involving the absorption of light by the 11-cis-retinal chromophore, which is a vitamin A derivative bound to rhodopsin and cone opsins of retinal photoreceptors[1]. When a photon of light in the visible range is absorbed, the cis-retinal can isomerize to all-trans-retinal[2]. The isomerization of retinal is important for the vision process, as it allows the retina to detect light of different wavelengths or colors. Small changes near the chromophore are enough to change its absorbance maxima, allowing organisms to sense light of different colors[3].
What Happens When an 11-cis-retinal Chromophore Absorbs Light?
When an 11-cis-retinal chromophore absorbs light, it undergoes isomerization to all-trans-retinal, initiating the visual signal. This process involves the excitation of an electron from its ground state into an excited state, leading to a conformational change in the retinal molecule. The absorption of a photon by the 11-cis-retinal requires input of energy, and the isomerization to all-trans-retinal is a key step in the visual cycle. The 11-cis-retinal is an essential component of visual pigments in photoreceptor cells, and its isomerization is a fundamental process in visual signal transduction[15][16][18].
Non-Ionizing Radiation Excites Electrons
Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to completely remove an electron from an atom or molecule. Instead, it has enough energy to excite electrons to move to a higher state, releasing photons of electromagnetic radiation such as visible light, near ultraviolet, and microwaves.
Molecules with Atoms in Higher Energy States React More
Molecules with atoms in higher energy states react more due to the concept of activation energy. Activation energy is the energy required to initiate a chemical reaction. According to collision theory, in order to effectively initiate a reaction, collisions must be sufficiently energetic to break chemical bonds, and this energy is known as the activation energy. As the temperature rises, molecules move faster and collide more vigorously, greatly increasing the likelihood of bond breakage upon collision. Therefore, the greater the temperature, the higher the probability that molecules will be moving with the necessary activation energy for a reaction to occur. Molecules with higher energy states have a greater probability of possessing the necessary activation energy for a reaction to occur, leading to increased reactivity.
What About Other Proteins?
Non-ionizing radiation (NIR) can affect proteins, including opsin proteins, by causing damage to their structure and function. To provide a general understanding of how non-ionizing radiation can affect proteins, consider the following points:
1. Alteration of protein structure and function: Non-ionizing radiation can cause significant damage to proteins through the disruption of peptide bonds and other structural modifications[5]. This can lead to changes in protein folding and function, which may affect the overall function of the protein.
2. Formation of reactive oxygen species (ROS): Exposure to non-ionizing radiation can generate ROS, which can cause oxidative stress and damage to proteins[5]. This damage can alter the structure and function of proteins, leading to potential health issues.
3. Targeting specific protein bonds: Certain protein bonds, such as disulfide bonds and carboxyl groups, are more susceptible to damage caused by non-ionizing radiation[5]. This damage can lead to the alteration of protein structure and function.
These points provide a general understanding of how non-ionizing radiation can affect proteins. If you are having unexplained damage in your body, re-read this, check the citations, and experiment to see if you feel better away from sources of non-ionizing radiation.
Citations:
[1] http://photobiology.info/Crouch.html
[2] https://chem.libretexts.org/Bookshelves/Biological_Chemistry/Supplemental_Modules_(Biological_Chemistry)/Photoreceptors/Chemistry_of_Vision
[3] https://chem.libretexts.org/Bookshelves/Biological_Chemistry/Supplemental_Modules_(Biological_Chemistry)/Photoreceptors/Chemistry_of_Vision/Cis-Trans_Isomerization_of_Retinal
[4] https://chem.libretexts.org/Bookshelves/Biological_Chemistry/Supplemental_Modules_(Biological_Chemistry)/Photoreceptors/Chemistry_of_Vision/Photochemical_Changes_in_Opsin
[5] https://en.wikipedia.org/wiki/Opsinhttps://en.wikipedia.org/wiki/Visual_phototransduction
[6] https://www.aocopm.org/assets/documents/10-31-11_Basic_Course_III_Orlando/ionizing%20an%20non.pdf
[7] https://www.frontiersin.org/articles/10.3389/fncel.2021.778900
[8] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1088937/
[9] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781858/
[10] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7443880/
[11] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8459055/
[12] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8616186/
[13] https://www.sciencedirect.com/science/article/pii/S0021925820532547
[14] https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/non-ionizing-radiation
[15] https://www.sciencedirect.com/topics/chemistry/11-cis-retinal
[17] https://www.sciencedirect.com/topics/nursing-and-health-professions/11-cis-retinal
[18] https://www.sas.upenn.edu/~tareilaj/TheEye.html
[19] https://pubs.acs.org/doi/10.1021/ja208789h
