104
Algae
zone. This model is consistent with ultrastructural data of electron microscopy. As above, the
functioning of the axonemal mechanics needs transient connections, which could possibly be
disrupted by intrinsic proteolytic activities due to the combined activities of a protease/ligase
system.
How a Paraxial Rod Works
Since the PFR and the axoneme are very tightly connected, both structures have to move together.
It can be argued that the PFR contributes to regulate the flagellar movements. This could be done
by providing a more rigid structure that can vary its stiffness in time, that is, modifying flagellumbeating pattern.
We need only one protein to build a device for information transfer and control, that is, a protein
with two conformational, alternate states such as intermediate filament proteins, which can form
lattice-like structures. The propagation of conformational changes along these proteins can be used
to transport and/or transduce sensory information. Each protein can be considered as a dipole in
one of the two possible states. We can imagine that the conformational change is transmitted by one
dipole to the neighbor proteins as a wave. Therefore, a current flow through these lattice-like structures could be generated by the mobile electrons of the proteins that interact with their immediate
neighbors via dipole–dipole forces.
The α-helical coiled-coil structural motif in the rod filament is well suited for electron propagation (Figure 2.36b). A current might be propagated distally, via PFR 1 and PFR 2 protein–protein
charge transfers in the lattice-like rod filaments. The current flows through these lattice-like structures and the sole constraint is that each lattice site should possess a dipole moment proportional to
the magnitude of the mobile charge unit and the distance over which it hops, that is, about 1–2 nm.
This wave produces a contraction in the PFR and a varying internal resistance that modulates the
flagellar beats. The contraction occurs by displacement of the goblet appendages of the PFR along
the axonemal microtubules, which reduces the distance between the coiled filaments, hence generating longitudinal waves of contraction along the paraxial rod. The stiffening should swing the
flagellum sideways, damping out some undulatory waves of the axoneme.
The phoTorecepTor apparaTa
In aquatic ecosystems, light is a physical factor of fundamental importance to both photosynthetic
and (nonphotosynthetic) heterotrophic organisms. They are able to sense and respond to light stimuli, an ability essential to optimize physiological processes, and to time their lives to feeding, reproduction, defense, and virtually all their functions. One of the most striking responses is phototaxis,
in which motile photosynthetic microorganisms adjust their swimming path with respect to incident
light in a finely tuned manner. Many are the advantages of phototaxis: it allows photosynthetic
organisms to position themselves for optimal light capture and efficient photosynthesis and facilitates avoidance responses in those situations where light is intense enough to damage pigments and
chloroplasts. In the case of many sexually reproducing species, such as Ulva sp. (Chlorophyta),
both female and male gametes show positive phototaxis, which may cause the colocalization of
both gametes near the surface of seawater improving the possibility of encountering. On the other
hand, zygotes usually become negatively phototactic, enabling them to swim towards the bottom
of the seashore where they can find a suitable substratum. Also, nonphotosynthetic organisms (heterotrophic) have shown to benefit the ecological advantages of phototaxis. For example, the marine
dinoflagellate predator Oxyrrhis marina can orient to light and is able to use photosensory response
to locate patches of phytoplankton prey by detection of chlorophyll a fluorescence.
The full exploitation of light information necessitates proper perceiving devices, able to change the
small signal represented by the light falling upon them in a larger signal and response of an entirely
different physical nature, that is, these devices, termed photoreceptors, must act as sensors, to perceive
wavelength and direction of light, as transducers, to convert the light signal not only into chemical
Algae
zone. This model is consistent with ultrastructural data of electron microscopy. As above, the
functioning of the axonemal mechanics needs transient connections, which could possibly be
disrupted by intrinsic proteolytic activities due to the combined activities of a protease/ligase
system.
How a Paraxial Rod Works
Since the PFR and the axoneme are very tightly connected, both structures have to move together.
It can be argued that the PFR contributes to regulate the flagellar movements. This could be done
by providing a more rigid structure that can vary its stiffness in time, that is, modifying flagellumbeating pattern.
We need only one protein to build a device for information transfer and control, that is, a protein
with two conformational, alternate states such as intermediate filament proteins, which can form
lattice-like structures. The propagation of conformational changes along these proteins can be used
to transport and/or transduce sensory information. Each protein can be considered as a dipole in
one of the two possible states. We can imagine that the conformational change is transmitted by one
dipole to the neighbor proteins as a wave. Therefore, a current flow through these lattice-like structures could be generated by the mobile electrons of the proteins that interact with their immediate
neighbors via dipole–dipole forces.
The α-helical coiled-coil structural motif in the rod filament is well suited for electron propagation (Figure 2.36b). A current might be propagated distally, via PFR 1 and PFR 2 protein–protein
charge transfers in the lattice-like rod filaments. The current flows through these lattice-like structures and the sole constraint is that each lattice site should possess a dipole moment proportional to
the magnitude of the mobile charge unit and the distance over which it hops, that is, about 1–2 nm.
This wave produces a contraction in the PFR and a varying internal resistance that modulates the
flagellar beats. The contraction occurs by displacement of the goblet appendages of the PFR along
the axonemal microtubules, which reduces the distance between the coiled filaments, hence generating longitudinal waves of contraction along the paraxial rod. The stiffening should swing the
flagellum sideways, damping out some undulatory waves of the axoneme.
The phoTorecepTor apparaTa
In aquatic ecosystems, light is a physical factor of fundamental importance to both photosynthetic
and (nonphotosynthetic) heterotrophic organisms. They are able to sense and respond to light stimuli, an ability essential to optimize physiological processes, and to time their lives to feeding, reproduction, defense, and virtually all their functions. One of the most striking responses is phototaxis,
in which motile photosynthetic microorganisms adjust their swimming path with respect to incident
light in a finely tuned manner. Many are the advantages of phototaxis: it allows photosynthetic
organisms to position themselves for optimal light capture and efficient photosynthesis and facilitates avoidance responses in those situations where light is intense enough to damage pigments and
chloroplasts. In the case of many sexually reproducing species, such as Ulva sp. (Chlorophyta),
both female and male gametes show positive phototaxis, which may cause the colocalization of
both gametes near the surface of seawater improving the possibility of encountering. On the other
hand, zygotes usually become negatively phototactic, enabling them to swim towards the bottom
of the seashore where they can find a suitable substratum. Also, nonphotosynthetic organisms (heterotrophic) have shown to benefit the ecological advantages of phototaxis. For example, the marine
dinoflagellate predator Oxyrrhis marina can orient to light and is able to use photosensory response
to locate patches of phytoplankton prey by detection of chlorophyll a fluorescence.
The full exploitation of light information necessitates proper perceiving devices, able to change the
small signal represented by the light falling upon them in a larger signal and response of an entirely
different physical nature, that is, these devices, termed photoreceptors, must act as sensors, to perceive
wavelength and direction of light, as transducers, to convert the light signal not only into chemical