Chirality is a property of
asymmetry
Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pre ...
important in several branches of science. The word ''chirality'' is derived from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
(''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable from its
mirror image
A mirror image (in a plane mirror) is a reflected duplication of an object that appears almost identical, but is reversed in the direction perpendicular to the mirror surface. As an optical effect it results from reflection off from substances ...
; that is, it cannot be
superimposed
Superimposition is the placement of one thing over another, typically so that both are still evident.
Graphics
In graphics, superimposition is the placement of an image or video on top of an already-existing image or video, usually to add to ...
onto it. Conversely, a mirror image of an ''achiral'' object, such as a sphere, cannot be distinguished from the object. A chiral object and its mirror image are called ''enantiomorphs'' (Greek, "opposite forms") or, when referring to molecules, ''
enantiomers
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical anti ...
''. A non-chiral object is called ''achiral'' (sometimes also ''amphichiral'') and can be superposed on its mirror image.
The term was first used by
Lord Kelvin
William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, Mathematical physics, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy (Glasgow), Professor of Natural Philoso ...
in 1893 in the second
Robert Boyle Lecture
The Robert Boyle Lecture is a lecture series delivered to the Oxford University Scientific Club (formerly the Oxford University Junior Scientific Club) at the University of Oxford, England. The first lecture was delivered in 1892.
The lectures ...
at the
Oxford University Junior Scientific Club
The Oxford University Scientific Society (OUSS) is a student scientific society at the University of Oxford. It was founded in 1882 as the Oxford University Junior Scientific Club. It is one of the oldest undergraduate science societies in the wo ...
which was published in 1894:
Human
hand
A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...
s are perhaps the most recognized example of chirality. The left hand is a non-superimposable mirror image of the right hand; no matter how the two hands are oriented, it is impossible for all the major features of both hands to coincide across all axes.
[Georges Henry Wagnière, ''On Chirality and the Universal Asymmetry: Reflections on Image and Mirror Image'' (2007).] This difference in symmetry becomes obvious if someone attempts to shake the right hand of a person using their left hand, or if a left-handed glove is placed on a right hand. In mathematics, ''chirality'' is the property of a figure that is not identical to its mirror image.
Mathematics
![Orbifold 2X](https://upload.wikimedia.org/wikipedia/commons/6/62/Orbifold_2X.2.svg)
In
mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...
, a figure is chiral (and said to have chirality) if it cannot be mapped to its mirror image by
rotation
Rotation, or spin, is the circular movement of an object around a '' central axis''. A two-dimensional rotating object has only one possible central axis and can rotate in either a clockwise or counterclockwise direction. A three-dimensional ...
s and
translation
Translation is the communication of the Meaning (linguistic), meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The ...
s alone. For example, a right shoe is different from a left shoe, and clockwise is different from anticlockwise. See for a full mathematical definition.
A chiral object and its mirror image are said to be enantiomorphs. The word ''enantiomorph'' stems from the Greek (enantios) 'opposite' + (morphe) 'form'. A non-chiral figure is called achiral or amphichiral.
The
helix
A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, ...
(and by extension a spun string, a screw, a propeller, etc.) and
Möbius strip
In mathematics, a Möbius strip, Möbius band, or Möbius loop is a surface that can be formed by attaching the ends of a strip of paper together with a half-twist. As a mathematical object, it was discovered by Johann Benedict Listing and Augu ...
are chiral two-dimensional objects in three-dimensional ambient space. The J, L, S and Z-shaped ''
tetromino
A tetromino is a geometric shape composed of four squares, connected orthogonally (i.e. at the edges and not the corners). Tetrominoes, like dominoes and pentominoes, are a particular type of polyomino. The corresponding polycube, called a tetracu ...
es'' of the popular video game
Tetris
''Tetris'' (russian: link=no, Тетрис) is a puzzle video game created by Soviet software engineer Alexey Pajitnov in 1984. It has been published by several companies for multiple platforms, most prominently during a dispute over the approp ...
also exhibit chirality, but only in a two-dimensional space.
Many other familiar objects exhibit the same chiral symmetry of the human body, such as gloves, glasses (sometimes), and shoes. A similar notion of chirality is considered in
knot theory
In the mathematical field of topology, knot theory is the study of knot (mathematics), mathematical knots. While inspired by knots which appear in daily life, such as those in shoelaces and rope, a mathematical knot differs in that the ends are ...
, as explained below.
Some chiral three-dimensional objects, such as the helix, can be assigned a right or left handedness, according to the
right-hand rule
In mathematics and physics, the right-hand rule is a common mnemonic for understanding orientation of axes in three-dimensional space. It is also a convenient method for quickly finding the direction of a cross-product of 2 vectors.
Most of th ...
.
Geometry
In
geometry
Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...
, a figure is achiral if — and only if — its
symmetry group
In group theory, the symmetry group of a geometric object is the group of all transformations under which the object is invariant, endowed with the group operation of composition. Such a transformation is an invertible mapping of the ambient ...
contains at least one ''orientation-reversing'' isometry.
In two dimensions, every figure that possesses an
axis of symmetry
Axial symmetry is symmetry around an axis; an object is axially symmetric if its appearance is unchanged if rotated around an axis. is achiral, and it can be shown that every ''bounded'' achiral figure must have an axis of symmetry.
In three dimensions, every figure that possesses a
plane of symmetry
In mathematics, reflection symmetry, line symmetry, mirror symmetry, or mirror-image symmetry is symmetry with respect to a reflection. That is, a figure which does not change upon undergoing a reflection has reflectional symmetry.
In 2D ther ...
or a center of symmetry is achiral. There are, however, achiral figures lacking both plane and center of symmetry.
In terms of
point groups
In geometry, a point group is a mathematical group of symmetry operations (isometries in a Euclidean space) that have a fixed point in common. The coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every p ...
, all chiral figures lack an improper axis of rotation (S
n). This means that they cannot contain a center of inversion (i) or a mirror plane (σ). Only figures with a point group designation of C
1, C
n, D
n, T, O, or I can be chiral.
Knot theory
A
knot
A knot is an intentional complication in cordage which may be practical or decorative, or both. Practical knots are classified by function, including hitches, bends, loop knots, and splices: a ''hitch'' fastens a rope to another object; a ' ...
is called
achiral
Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable from i ...
if it can be continuously deformed into its mirror image, otherwise it is called chiral. For example, the
unknot
In the mathematical theory of knots, the unknot, not knot, or trivial knot, is the least knotted of all knots. Intuitively, the unknot is a closed loop of rope without a knot tied into it, unknotted. To a knot theorist, an unknot is any embe ...
and the
figure-eight knot
The figure-eight knot or figure-of-eight knot is a type of stopper knot. It is very important in both sailing and rock climbing as a method of stopping ropes from running out of retaining devices. Like the overhand knot, which will jam under st ...
are achiral, whereas the
trefoil knot
In knot theory, a branch of mathematics, the trefoil knot is the simplest example of a nontrivial knot. The trefoil can be obtained by joining together the two loose ends of a common overhand knot, resulting in a knotted loop. As the simplest kno ...
is chiral.
Physics
In physics, chirality may be found in the
spin
Spin or spinning most often refers to:
* Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning
* Spin, the rotation of an object around a central axis
* Spin (propaganda), an intentionally b ...
of a particle, where the handedness of the object is determined by the direction in which the particle spins. Not to be confused with
helicity, which is the projection of the spin along the linear momentum of a subatomic particle, chirality is an intrinsic quantum mechanical property, like spin. Although both chirality and helicity can have left-handed or right-handed properties, only in the massless case are they identical.
In particular for a massless particle the helicity is the same as the chirality while for an antiparticle they have opposite sign.
The ''handedness'' in both chirality and helicity relate to the rotation of a particle while it proceeds in linear motion with reference to the human hands. The thumb of the hand points towards the direction of linear motion whilst the fingers curl into the palm, representing the direction of rotation of the particle (i.e. clockwise and counterclockwise). Depending on the linear and rotational motion, the particle can either be defined by left-handedness or right-handedness.
A symmetry transformation between the two is called
parity
Parity may refer to:
* Parity (computing)
** Parity bit in computing, sets the parity of data for the purpose of error detection
** Parity flag in computing, indicates if the number of set bits is odd or even in the binary representation of the r ...
. Invariance under parity by a
Dirac fermion
In physics, a Dirac fermion is a spin-½ particle (a fermion) which is different from its antiparticle. The vast majority of fermions – perhaps all – fall under this category.
Description
In particle physics, all fermions in the standard model ...
is called ''chiral symmetry''.
Electromagnetism
Electromagnetic
In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
waves can have handedness associated with their
polarization. Polarization of an
electromagnetic wave
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visib ...
is the property that describes the
orientation
Orientation may refer to:
Positioning in physical space
* Map orientation, the relationship between directions on a map and compass directions
* Orientation (housing), the position of a building with respect to the sun, a concept in building de ...
, i.e., the
time-varying direction and
amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...
, of the
electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
vector
Vector most often refers to:
*Euclidean vector, a quantity with a magnitude and a direction
*Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism
Vector may also refer to:
Mathematic ...
. For example, the electric field vectors of left-handed or right-handed
circularly polarized waves form helices of opposite handedness in space.
Circularly polarized waves of opposite handedness propagate through chiral media at different speeds (
circular birefringence) and with different losses (
circular dichroism). Both phenomena are jointly known as optical activity. Circular birefringence causes rotation of the polarization state of electromagnetic waves in chiral media and can cause a
negative index of refraction for waves of one handedness when the effect is sufficiently large.
While optical activity occurs in structures that are chiral in three dimensions (such as helices), the concept of chirality can also be applied in two dimensions.
2D-chiral patterns, such as flat spirals, cannot be superimposed with their mirror image by translation or rotation in two-dimensional space (a plane). 2D chirality is associated with directionally asymmetric transmission (reflection and absorption) of circularly polarized waves. 2D-chiral materials, which are also anisotropic and lossy exhibit different total transmission (reflection and absorption) levels for the same circularly polarized wave incident on their front and back. The asymmetric transmission phenomenon arises from different, e.g. left-to-right, circular polarization conversion efficiencies for opposite propagation directions of the incident wave and therefore the effect is referred to as circular conversion dichroism.
Like the twist of a 2d-chiral pattern appears reversed for opposite directions of observation, 2d-chiral materials have interchanged properties for left-handed and right-handed circularly polarized waves that are incident on their front and back. In particular left-handed and right-handed circularly polarized waves experience opposite directional transmission (reflection and absorption) asymmetries.
While optical activity is associated with 3d chirality and circular conversion is associated with 2d chirality, both effects have also been observed in structures that are not chiral by themselves. For the observation of these chiral electromagnetic effects, chirality does not have to be an intrinsic property of the material that interacts with the electromagnetic wave. Instead, both effects can also occur when the propagation direction of the electromagnetic wave together with the structure of an (achiral) material form a chiral experimental arrangement. This case, where the mutual arrangement of achiral components forms a chiral (experimental) arrangement, is known as extrinsic chirality.
Chiral mirrors are a class of metamaterials that reflect circularly polarized light of a certain helicity in a handedness-preserving manner, while absorbing circular polarization of the opposite handedness. However, most absorbing chiral mirrors operate only in a narrow frequency band, as limited by the causality principle. Employing a different design methodology that allows undesired waves to pass through instead of absorbing the undesired waveform, chiral mirrors are able to show good broadband performance.
Chemistry
![Zwitterion-Alanine](https://upload.wikimedia.org/wikipedia/commons/4/4a/Zwitterion-Alanine.png)
A ''chiral molecule'' is a type of
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
that has a non-superposable
mirror image
A mirror image (in a plane mirror) is a reflected duplication of an object that appears almost identical, but is reversed in the direction perpendicular to the mirror surface. As an optical effect it results from reflection off from substances ...
. The feature that is most often the cause of chirality in molecules is the presence of an
asymmetric carbon atom An asymmetric carbon atom (chiral carbon) is a carbon atom that is attached to four different types of atoms or groups of atoms. Le Bel-van't Hoff rule states that the number of stereoisomers of an organic compound is 2n, where n represents the num ...
.
The term "chiral" in general is used to describe the object that is non-superposable on its mirror image.
In chemistry, chirality usually refers to molecules. Two mirror images of a chiral molecule are called
enantiomer
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...
s or optical
isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers.
Iso ...
s. Pairs of enantiomers are often designated as "
right-", "left-handed" or, if they have no bias, "achiral". As polarized light passes through a chiral molecule, the plane of polarization, when viewed along the axis toward the source, will be rotated clockwise (to the right) or anticlockwise (to the left). A right handed rotation is dextrorotary (d); that to the left is levorotary (l). The d- and l-isomers are the same compound but are called
enantiomers
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical anti ...
. An equimolar mixture of the two optical isomers, which is called a
racemic mixture
In chemistry, a racemic mixture, or racemate (), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates. ...
, will produce no net rotation of polarized light as it passes through. Left handed molecules have l- prefixed to their names; d- is prefixed to right handed molecules. However, this ''d-'' and ''l-'' notation of distinguishing enantiomers does not say anything about the actual spatial arrangement of the ligands/substituents around the
stereogenic
In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups cr ...
center, which is defined as configuration. Another nomenclature system employed to specify configuration is Fischer convention. This is also referred to as the D- and L-system. Here the relative configuration is assigned with reference to D-(+)-Glyceraldehyde and L-(-)-Glyceraldehyde, being taken as standard. Fischer convention is widely used in sugar chemistry and for α-amino acids. Due to the drawbacks of Fischer convention, it is almost entirely replaced by
Cahn-Ingold-Prelog convention, also known as the sequence rule or R and S nomenclature. This was further extended to assign absolute configuration to ''cis-trans'' isomers with the E-Z notation.
Molecular chirality is of interest because of its application to
stereochemistry
Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereois ...
in
inorganic chemistry
Inorganic chemistry deals with synthesis and behavior of inorganic and organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subjects of organic chemistry. The distinction between the two disci ...
,
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...
,
physical chemistry
Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mecha ...
,
biochemistry
Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology and ...
, and
supramolecular chemistry
Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces, ...
.
More recent developments in chiral chemistry include the development of chiral inorganic nanoparticles that may have the similar tetrahedral geometry as chiral centers associated with sp3 carbon atoms traditionally associated with chiral compounds, but at larger scale. Helical and other symmetries of chiral nanomaterials were also obtained.
Biology
All of the known life-forms show specific chiral properties in chemical structures as well as macroscopic anatomy, development and behavior. In any specific organism or evolutionarily related set thereof, individual compounds, organs, or behavior are found in the same single enantiomorphic form. Deviation (having the opposite form) could be found in a small number of chemical compounds, or certain organ or behavior but that variation strictly depends upon the genetic make up of the organism. From chemical level (molecular scale), biological systems show extreme stereospecificity in synthesis, uptake, sensing, metabolic processing. A living system usually deals with two enantiomers of the same compound in drastically different ways.
In biology, homochirality is a common property of
amino acids
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
and
carbohydrates
In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or may ...
. The chiral
protein-making amino acids, which are translated through the ribosome from genetic coding, occur in the
L form. However,
D-amino acids are also found in nature. The monosaccharides (carbohydrate-units) are commonly found in
D-configuration. DNA double helix is chiral (as any kind of
helix
A helix () is a shape like a corkscrew or spiral staircase. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, ...
is chiral), and
B-form of DNA shows a right-handed turn.
Sometimes, when two enantiomers of a compound found in organisms, they significantly differ in their taste, smell and other biological actions. For example, (+)-limonene found in orange (causing its smell), and (–)-limonene found in lemons (causing its smell), show different smells due to different biochemical interactions at human nose. (+)-
Carvone
Carvone is a member of a family of chemicals called terpenoids. Carvone is found naturally in many essential oils, but is most abundant in the oils from seeds of caraway (''Carum carvi''), spearmint (''Mentha spicata''), and dill.
Uses
Both carvo ...
is responsible for the smell of
caraway
Caraway, also known as meridian fennel and Persian cumin (''Carum carvi''), is a biennial plant in the family Apiaceae, native to western Asia, Europe, and North Africa.
Etymology
The etymology of "caraway" is unclear. Caraway has been ...
seed oil, whereas (–)-carvone is responsible for smell of
spearmint
Spearmint, also known as garden mint, common mint, lamb mint and mackerel mint, is a species of mint, ''Mentha spicata'' (, native to Europe and southern temperate Asia, extending from Ireland in the west to southern China in the east. It is nat ...
oil.
Also, for artificial compounds, including medicines, in case of
chiral drugs
Chemical compounds that come as mirror-image pairs are referred to by chemists as chiral or handed molecules. Each twin is called an enantiomer. Drugs that exhibit handedness are referred to as chiral drugs. Chiral drugs that are equimolar (1:1) mi ...
, the two enantiomers sometimes show remarkable difference in effect of their biological actions. Darvon (
dextropropoxyphene
Dextropropoxyphene is an analgesic in the opioid category, patented in 1955 and manufactured by Eli Lilly and Company. It is an optical isomer of levopropoxyphene. It is intended to treat mild pain and also has antitussive (cough suppressant) a ...
) is a painkiller, whereas its enantiomer, Novrad (
levopropoxyphene
Levopropoxyphene is an antitussive. It is an optical isomer of dextropropoxyphene. The racemic mixture is called propoxyphene. Only the dextro-isomer (dextropropoxyphene) has an analgesic effect; the levo-isomer appears to exert only an antitussi ...
) is an anti-cough agent. In case of
penicillamine
Penicillamine, sold under the brand name of Cuprimine among others, is a medication primarily used for the treatment of Wilson's disease. It is also used for people with kidney stones who have high urine cystine levels, rheumatoid arthritis, an ...
, the (''S''-isomer is used in the treatment of primary chronic arthritis, whereas the (''R'')-isomer has no therapeutic effect, as well as being highly toxic. In some cases, the less therapeutically active enantiomer can cause side effects. For example, (''S''-naproxen is an analgesic but the (''R''-isomer causes renal problems. In such situations where one of the enantiomers of a racemic drug is active and the other partner has undesirable or toxic effect one may switch from racemate to a single enantiomer drug for a better therapeutic valu
Such a switching from a racemic drug to an enantiopure drug is called a
chiral switch The word "chiral switch" was introduced by Agranat and Caner in 1999. Chiral switches are chiral drugs that are already approved as racemates but that have been re-developed as single enantiomers. The term chiral switching has been coined to descr ...
.
The naturally occurring plant form of alpha-tocopherol (
vitamin E
Vitamin E is a group of eight fat soluble compounds that include four tocopherols and four tocotrienols. Vitamin E deficiency, which is rare and usually due to an underlying problem with digesting dietary fat rather than from a diet low in vitami ...
) is RRR-α-tocopherol whereas the synthetic form (all-racemic vitamin E, or dl-tocopherol) is equal parts of the stereoisomers RRR, RRS, RSS, SSS, RSR, SRS, SRR, and SSR with progressively decreasing biological equivalency, so that 1.36 mg of dl-tocopherol is considered equivalent to 1.0 mg of d-tocopherol.
Macroscopic examples of chirality are found in the plant kingdom, the animal kingdom and all other groups of organism. A simple example is the coiling direction of any climber plant, which can grow to form either a left- or right-handed helix.
In anatomy, chirality is found in the imperfect mirror image symmetry of many kinds of animal bodies. Organisms such as
gastropod
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...
s exhibit chirality in their coiled shells, resulting in an asymmetrical appearance. Over 90% of gastropod species have ''dextral'' (right-handed) shells in their coiling, but a small minority of species and genera are virtually always ''sinistral'' (left-handed). A very few species (for example ''
Amphidromus perversus
''Amphidromus perversus'' is a species of air-breathing land snail, a Terrestrial animal, terrestrial pulmonate gastropod mollusk in the family Camaenidae. MolluscaBase eds. (2020). MolluscaBase. Amphidromus perversus (Linnaeus, 1758). Accessed t ...
''
) show an equal mixture of dextral and sinistral individuals.
In humans, chirality (also referred to as ''handedness'' or ''laterality'') is an attribute of humans defined by their unequal distribution of
fine motor skill
Fine motor skill (or dexterity) is the coordination of small muscles in movement with the eyes, hands and fingers. The complex levels of manual dexterity that humans exhibit can be related to the nervous system. Fine motor skills aid in the growt ...
between the left and right
hands
A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each " ...
. An individual who is more
dexterous
Fine motor skill (or dexterity) is the coordination of small muscles in movement with the eyes, hands and fingers. The complex levels of manual dexterity that humans exhibit can be related to the nervous system. Fine motor skills aid in the growt ...
with the right hand is called ''
right-handed
In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to it being stronger, faster or more dextrous. The other hand, comparatively often the weaker, less dextrous or simply less subjecti ...
'', and one who is more skilled with the left is said to be ''
left-handed
In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to it being stronger, faster or more dextrous. The other hand, comparatively often the weaker, less dextrous or simply less subjecti ...
''. Chirality is also seen in the study of
facial asymmetry
Facial symmetry is one specific measure of bodily symmetry. Along with traits such as averageness and youthfulness it influences judgments of aesthetic traits of physical attractiveness and beauty. For instance, in mate selection, people have be ...
.
In the case of the health condition ''
situs inversus totalis
Situs inversus (also called situs transversus or oppositus) is a congenital condition in which the major visceral organs are reversed or mirrored from their normal positions. The normal arrangement of internal organs is known as situs solitus. Al ...
'', in which all the internal organs are flipped horizontally (i.e. the heart
placed slightly to the right instead of the left), chirality poses some problems should the patient require a liver or heart transplant, as these organs are chiral, thus meaning that the blood vessels which supply these organs would need to be rearranged should a normal, non ''situs inversus'' (''
situs solitus'') organ be required.
In the monocot
bloodroot family, the species of the
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
''
Wachendorfia
''Wachendorfia'' is a genus of perennial herbaceous plants that is assigned to the bloodroot family. The plants have a perennial rootstock with red sap. From the rootstock emerge lance- or line-shaped, sometime sickle-shaped, pleated, simple lea ...
'' and ''
Barberetta
''Barberetta'' is a genus of herbaceous perennial plants in the family Haemodoraceae. It contains only one known species, ''Barberetta aurea''.
Description
''Barberetta aurea'' grows to up to high from a tuberous rootstock and develops about ...
'' have only individuals that either have the style points to the right or the style pointed to the left, with both morphs appearing within the same populations. This is thought to increase
outcrossing
Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity.
Outcrossing can be a useful ...
and so boost genetic diversity, which in turn may help to survive in a changing environment. Remarkably, the related genus ''
Dilatris
''Dilatris'' is a genus of four species of evergreen perennial herbaceous plants of up to high, that are assigned to the bloodroot family. The plants have hairless, line- to lance-shaped leaves set in a fan that emerges from a red or orange col ...
'' also has chiraly dimorphic flowers, but here both morphs occur on the same plant.
In flatfish, the
summer flounder
The summer flounder or fluke (''Paralichthys dentatus'') is a marine flatfish that is found in the Atlantic Ocean off the East Coast of the United States and Canada. It is especially abundant in waters from North Carolina to Massachusetts.
De ...
or fluke are left-eyed, while
halibut
Halibut is the common name for three flatfish in the genera '' Hippoglossus'' and ''Reinhardtius'' from the family of right-eye flounders and, in some regions, and less commonly, other species of large flatfish.
The word is derived from ''h ...
are right-eyed.
See also
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Handedness
In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to it being stronger, faster or more Fine motor skill, dextrous. The other hand, comparatively often the weaker, less dextrous or sim ...
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Chiral drugs
Chemical compounds that come as mirror-image pairs are referred to by chemists as chiral or handed molecules. Each twin is called an enantiomer. Drugs that exhibit handedness are referred to as chiral drugs. Chiral drugs that are equimolar (1:1) mi ...
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Chiral switch The word "chiral switch" was introduced by Agranat and Caner in 1999. Chiral switches are chiral drugs that are already approved as racemates but that have been re-developed as single enantiomers. The term chiral switching has been coined to descr ...
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Chiral inversion Chiral inversion is the process of conversion of one enantiomer of a chiral molecule to its mirror-image version with no other change in the molecule.
Chiral inversion happens depending on various factors (viz. biological-, solvent-, light-, temper ...
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Metachirality Metachirality is a stronger form of chirality.
It applies to objects or systems that are chiral (not identical to their mirror image) and where, in addition, their mirror image has a symmetry group that differs from the symmetry group of the origina ...
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Orientation (space)
In mathematics, orientability is a property of some topological spaces such as real vector spaces, Euclidean spaces, Surface (topology), surfaces, and more generally manifolds that allows a consistent definition of "clockwise" and "counterclo ...
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Sinistral and dextral
Sinistral and dextral, in some scientific fields, are the two types of chirality (" handedness") or relative direction. The terms are derived from the Latin words for "left" (''sinister'') and "right" (''dexter''). Other disciplines use different ...
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Tendril perversion
Tendril perversion is a geometric phenomenon sometimes observed in helical structures in which the direction of the helix transitions between left-handed and right-handed. Such a reversal of chirality is commonly seen in helical plant tendril ...
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Chirality (physics)
A chiral phenomenon is one that is not identical to its mirror image (see the article on mathematical chirality). The spin of a particle may be used to define a handedness, or helicity, for that particle, which, in the case of a massless particl ...
References
External links
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{{Navbox stereochemistry
1890s neologisms
Biochemistry
Origin of life
Stereochemistry
Pharmacology
de:Chiralität (Chemie)