hieroglyphs carved out of stone such that they are mirrored on both sides of the
so-called ankh cross. This ankh cross plays an important role in the Egyptian
mythology representing the symbol for live. The pharaohs firmly believed in life
after death, and accordingly, they wanted to link the symbol for life with their coffins
as well as the mural paintings and stelae of the burial chamber. In addition, the
hieroglyphs closely related to the ankh cross are appearing twice, that is, in the form
of their two mirror images. This ancient interpretation of chirality/life/death is well in
line with our modern convention to assume life processes, for example, enzymatic
transformation processes, to be highly enantioselective, but also dead organic matter
may be transformed and in part mineralised by very enantioselective processes.
1.3 Chirality in Living Organisms
Detailed evidence for the influence of symmetry and asymmetry on life processes
and the obvious consequences for our daily life can be found in the realm of plants
and animals, where numerous examples for symmetric and asymmetric macroscopic
structures can be observed (Schilthuizen and Davison 2005; Makela and Annila
2010; Barron 2012a, b; Wensink and Morales-Anda 2015; Jedrzejewska and
Szumna 2017). For example, the occurrence of a horizontal radial symmetric
shape for plants may be attributed to the influence of the sun light, which circles
around the stem in the course of a day. Branches and leaves tend to grow towards the
light, whereas roots are not at all attracted by light but rather follow the gravitational
force. Wherever the symmetric lateral plane is being placed, it will divide the object
into (more or less) equal parts. On the other hand, a special case of radial symmetry,
the so-called bilateral symmetry, is also often encountered in the realm of plants and
animals. These kinds of objects only possess one vertical or horizontal internal plane
of symmetry, sometimes referred to as “mirror plane”. A symmetry of this kind can
be found for the human body. The symmetric plane divides the human body
vertically into two more or less even parts with one ear, one eye, one nostril, one
arm and one leg at each side. This type of symmetry is closely connected to the
evolutionary development of the organism. In general, animals that are sessile and
do not move are assumed to show a classical bilateral symmetry, while organisms
that have developed locomotive properties are preferentially characterised by radial
symmetry. However, many exceptions from this rule can be found in natural
systems, and, in addition, spherical, conical, cylindrical symmetries are also
encountered.
On the other hand, macroscopic asymmetric structures possessing no plane of
symmetry are also quite general in nature. Classic examples for asymmetric objects
are helical structures, which are found for climbing and twining plants. For example,
the “honeysuckle (Linnaea borealis L.)” always twines in a left-handed helix,
whereas the “morning glory (Convolvulus sabatius L.)” twines in a right-handed
helix. Helical structures are also known for animals. Most prominent examples can
be found for marine and freshwater molluscs (snails and shells). Normally, only one
1.3 Chirality in Living Organisms
3
so-called ankh cross. This ankh cross plays an important role in the Egyptian
mythology representing the symbol for live. The pharaohs firmly believed in life
after death, and accordingly, they wanted to link the symbol for life with their coffins
as well as the mural paintings and stelae of the burial chamber. In addition, the
hieroglyphs closely related to the ankh cross are appearing twice, that is, in the form
of their two mirror images. This ancient interpretation of chirality/life/death is well in
line with our modern convention to assume life processes, for example, enzymatic
transformation processes, to be highly enantioselective, but also dead organic matter
may be transformed and in part mineralised by very enantioselective processes.
1.3 Chirality in Living Organisms
Detailed evidence for the influence of symmetry and asymmetry on life processes
and the obvious consequences for our daily life can be found in the realm of plants
and animals, where numerous examples for symmetric and asymmetric macroscopic
structures can be observed (Schilthuizen and Davison 2005; Makela and Annila
2010; Barron 2012a, b; Wensink and Morales-Anda 2015; Jedrzejewska and
Szumna 2017). For example, the occurrence of a horizontal radial symmetric
shape for plants may be attributed to the influence of the sun light, which circles
around the stem in the course of a day. Branches and leaves tend to grow towards the
light, whereas roots are not at all attracted by light but rather follow the gravitational
force. Wherever the symmetric lateral plane is being placed, it will divide the object
into (more or less) equal parts. On the other hand, a special case of radial symmetry,
the so-called bilateral symmetry, is also often encountered in the realm of plants and
animals. These kinds of objects only possess one vertical or horizontal internal plane
of symmetry, sometimes referred to as “mirror plane”. A symmetry of this kind can
be found for the human body. The symmetric plane divides the human body
vertically into two more or less even parts with one ear, one eye, one nostril, one
arm and one leg at each side. This type of symmetry is closely connected to the
evolutionary development of the organism. In general, animals that are sessile and
do not move are assumed to show a classical bilateral symmetry, while organisms
that have developed locomotive properties are preferentially characterised by radial
symmetry. However, many exceptions from this rule can be found in natural
systems, and, in addition, spherical, conical, cylindrical symmetries are also
encountered.
On the other hand, macroscopic asymmetric structures possessing no plane of
symmetry are also quite general in nature. Classic examples for asymmetric objects
are helical structures, which are found for climbing and twining plants. For example,
the “honeysuckle (Linnaea borealis L.)” always twines in a left-handed helix,
whereas the “morning glory (Convolvulus sabatius L.)” twines in a right-handed
helix. Helical structures are also known for animals. Most prominent examples can
be found for marine and freshwater molluscs (snails and shells). Normally, only one
1.3 Chirality in Living Organisms
3