Citizendia

Olfactory receptors expressed in the cell membranes of olfactory receptor neurons are responsible for the detection of odor molecules. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer An olfactory receptor neuron also called an olfactory sensory neuron is the primary transduction cell in the Olfactory system. Activated olfactory receptors are the initial player in a signal transduction cascade which ultimately produces a nerve impulse which is transmitted to the brain. In Biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal These receptors are members of the class A rhodopsin-like family of G protein-coupled receptors. Rhodopsin-like receptors are the largest group of G-protein coupled receptors G-protein-coupled receptors GPCRs constitute a vast protein family that encompasses G protein-coupled receptors ( GPCRs) also known as seven transmembrane domain receptors, 7TM receptors, heptahelical receptors, and [1]

Contents

Expression

In vertebrates, the olfactory receptors are located in the cilia of the olfactory sensory neurons. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes [2] In insects, olfactory receptors are located on the antennae. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Antennae (singular antenna) are paired Appendages connected to the front-most segments of Arthropods In Crustaceans they are [3] Sperm cells also express odor receptors, which are thought to be involved in chemotaxis to find the egg cell. The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. Chemotaxis, a kind of Taxis, is the phenomenon in which bodily cells bacteria, and other single-cell or Multicellular organisms direct their movements An ovum (plural ova) is a Haploid Female reproductive cell or Gamete. [4]

Mechanism

Rather than binding specific ligands like most receptors, olfactory receptors display affinity for a range of odor molecules and conversely a single odorant molecule may bind to a number of olfactory receptors with varying affinities. In Biochemistry, a receptor is a Protein molecule embedded in either the Plasma membrane or Cytoplasm of a cell to which a mobile signaling [5] Once the odorant has bound to the odor receptor, the receptor undergoes structural changes and it binds and activates the olfactory-type G protein on the inside of the olfactory receptor neuron. GTP chemical structurepng|thumb|180px| Guanosine triphosphate]] G proteins short for guanine nucleotide-binding proteins, are a family of Proteins involved The G protein (Golf and/or Gs)[6] in turn activates the lyase - adenylate cyclase - which converts ATP into cyclic AMP (cAMP). "G protein" usually refers to the membrane-associated heterotrimeric G proteins, sometimes referred to as the "large" G proteins. Guanine nucleotide binding protein (G protein alpha activating activity polypeptide olfactory type, also known as GNAL, is a human Gene. GNAS complex locus, also known as GNAS, is a human Gene. Adenylate cyclase ( also known as adenylyl cyclase or AC) is a Lyase Enzyme. Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Cyclic adenosine monophosphate ( cAMP, cyclic AMP or 3'-5'-cyclic Adenosine monophosphate) is a Second messenger that is important in many biological The cAMP opens cyclic nucleotide-gated ion channels which allow calcium and sodium ions to enter into the cell, depolarizing the olfactory receptor neuron and beginning an action potential which carries the information to the brain. A cyclic nucleotide-gated (CNG ion channel is any Ion channel that opens in the presence of Cyclic nucleotides Mechanism The channels are gated by Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge In Neurophysiology, the action potential is a self-regenerating Wave of Electrochemical activity that allows Nerve cells to carry a signal The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain

Diversity

There are a wide range of different odor receptors, with as many as 1,000 in the mammalian genome which represents approximately 3% of the genes in the genome. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby However not all of these potential odor receptor genes are expressed and are functional. According to an analysis of data derived from the human genome project, humans have approximately 400 functional genes coding for olfactory receptors and the remaining 600 candidates are pseudogenes. The Human Genome Project (HGP was an international Scientific research project with a primary goal to determine the sequence of chemical base pairs which make up DNA History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Pseudogenes are defunct relatives of known Genes that have lost their Protein -coding ability or are otherwise no longer expressed [7]

The reason for the large number of different odor receptors is to provide a system for discriminating between as many different odors as possible. Even so, each odor receptor does not detect a single odor. Rather each individual odor receptor is broadly tuned to be activated by a number of similar odorant structures. [8][9] Analogous to the immune system, the diversity that exists within the olfactory receptor family allows molecules that have never been encountered before to be characterized. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Furthermore most odors activate more than one type of odor receptor. Since the number of combinations and permutations of olfactory receptors is almost limitless, the olfactory receptor system is capable of detecting and distinguishing between a practically infinite number of odorant molecules. Combinatorics is a branch of Pure mathematics concerning the study of discrete (and usually finite) objects

Families

A nomenclature system has been devised for the olfactory receptor family[10] and is the basis for the official Human Genome Project (HUGO) symbols for the genes that encode these receptors. Gene nomenclature is the scientific naming of Genes, the units of heredity in living organisms The Human Genome Organisation (HUGO is an organization involved in the Human Genome Project, a project about mapping the human genome History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance The names of individual olfactory receptor family members are in the format "ORnXm" where:

For example OR1A1 is the first isoform of subfamily A of olfactory receptor family 1.

Members belonging to the same subfamily of olfactory receptors (>60% sequence identity) are likely to recognize structurally similar odorant molecules. [11]

Two major classes of olfactory receptors have been identified in humans:[12]

Discovery

In 2004 Linda B. Buck and Richard Axel won the Nobel Prize in Physiology or Medicine for their work on olfactory receptors. Tetrapods ( Greek τετραποδη tetrapoda, Latin Quadruped, "four-footed" are Vertebrate Animals "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Linda B Buck, PhD, (born January 29, 1947) is an American Biologist best known for her work on the Olfactory system Richard Axel (born July 2, 1946, New York City) is an American Neuroscientist whose work on the Olfactory system won him The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin is awarded once a year by the Swedish Karolinska Institute. [13][14] In 2006 it was shown that another class of odorant receptors exist for volatile amines. Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair. [15] This class of receptors consists of the trace amine-associated receptors (TAAR) with the exception of TAAR1 which is a receptor for thyronamines. Trace amine-associated receptors, abbreviated TAAR and previously abbreviated TAR and TA, are a class of G protein-coupled receptors identified Thyronamine refers both to a molecule and to derivatives of that molecule a family of decarboxylated and deiodinated Metabolites of the Thyroid

Unfortunately, there is still a lack of experimental structures at atomic level for olfactory receptors and structural information is based on homology modeling methods. Olfactory receptors expressed in the Cell membranes of Olfactory receptor neurons are responsible for the detection of Odor molecules In Protein structure prediction, homology modeling, also known as comparative modeling, is a class of methods for constructing an atomic-resolution model of a [16]

See also

References

  1. ^ Gaillard I, Rouquier S, Giorgi D (2004). In Biochemistry, a receptor is a Protein molecule embedded in either the Plasma membrane or Cytoplasm of a cell to which a mobile signaling Trace amine-associated receptors, abbreviated TAAR and previously abbreviated TAR and TA, are a class of G protein-coupled receptors identified "Olfactory receptors". Cell. Mol. Life Sci. 61 (4): 456–69. doi:10.1007/s00018-003-3273-7. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 14999405.  
  2. ^ Rinaldi A (2007). "The scent of life. The exquisite complexity of the sense of smell in animals and humans". EMBO Rep. 8 (7): 629–33. doi:10.1038/sj.embor.7401029. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 17603536.  
  3. ^ Hallem EA, Dahanukar A, Carlson JR (2006). "Insect odor and taste receptors". Annu. Rev. Entomol. 51: 113–35. doi:10.1146/annurev.ento.51.051705.113646. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16332206.  
  4. ^ Spehr M, Schwane K, Riffell JA, Zimmer RK, Hatt H (2006). "Odorant receptors and olfactory-like signaling mechanisms in mammalian sperm". Mol. Cell. Endocrinol. 250 (1-2): 128–36. doi:10.1016/j.mce.2005.12.035. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16413109.  
  5. ^ Buck LB (2004). "Olfactory receptors and odor coding in mammals". Nutr. Rev. 62 (11 Pt 2): S184–8; discussion S224–41. doi:10.1301/nr.2004.nov.S184-S188. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 15630933.  
  6. ^ Jones DT, Reed RR (1989). "Golf: an olfactory neuron specific-G protein involved in odorant signal transduction". Science 244 (4906): 790-5. doi:10.1126/science.2499043. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 2499043.  
  7. ^ Gilad Y, Lancet D (2003). "Population differences in the human functional olfactory repertoire". Mol. Biol. Evol. 20 (3): 307–14. doi:10.1093/molbev/msg013. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 12644552.  
  8. ^ Malnic B, Hirono J, Sato T, Buck LB (1999). "Combinatorial receptor codes for odors". Cell 96 (5): 713–23. doi:10.1016/S0092-8674(00)80581-4. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 10089886.  
  9. ^ Araneda RC, Peterlin Z, Zhang X, Chesler A, Firestein S (2004). "A pharmacological profile of the aldehyde receptor repertoire in rat olfactory epithelium". J. Physiol. (Lond. ) 555 (Pt 3): 743–56. doi:10.1113/jphysiol.2003.058040. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 14724183.  
  10. ^ Glusman G, Bahar A, Sharon D, Pilpel Y, White J, Lancet D (2000). "The olfactory receptor gene superfamily: data mining, classification, and nomenclature". Mamm. Genome 11 (11): 1016–23. doi:10.1007/s003350010196. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 11063259.  
  11. ^ Malnic B, Godfrey PA, Buck LB (2004). "The human olfactory receptor gene family". Proc. Natl. Acad. Sci. U. S. A. 101 (8): 2584–9. doi:10.1073/pnas.0307882100. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 14983052.  
  12. ^ Glusman G, Yanai I, Rubin I, Lancet D (2001). "The complete human olfactory subgenome". Genome Res. 11 (5): 685–702. doi:10.1101/gr.171001. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 11337468.  
  13. ^ Buck L, Axel R (1991). "A novel multigene family may encode odorant receptors: a molecular basis for odor recognition". Cell 65 (1): 175–87. doi:10.1016/0092-8674(91)90418-X. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 1840504.  
  14. ^ Press Release: The 2004 Nobel Prize in Physiology or Medicine. Retrieved on 2007-06-06. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1508 - Maximilian I Holy Roman Emperor, is defeated in Friulia by Venetian forces; he is forced to sign a three-year
  15. ^ Liberles SD, Buck LB (2006). "A second class of chemosensory receptors in the olfactory epithelium". Nature 442 (7103): 645–50. doi:10.1038/nature05066. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16878137.  
  16. ^ Khafizov K, Anselmi C, Menini A, Carloni P (2007). "Ligand specificity of odorant receptors". J Mol Model 13 (3): 401–9. doi:10.1007/s00894-006-0160-9. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 17120078.  

External links

Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books
© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
 Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic