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Algae
As described above, changes in the motion trajectory by bending of the locomotory flagellum
are due to the screening of the photoreceptor by the eyespot that changes the electrostatic field. The
locomotory flagellum carries the paraxial rod (PAR; Figure 2.36a and b), a hollow rod-like structure
with a diameter of 90 nm along the entire length. The PAR is the true effector. When the photoreceptor is screened by the eyespot, the signaling state of the protein becomes the dominant isomer and a
change in the electrostatic field occurs. Since the photoreceptor and the paraxial rod are a structural
unit (Figure 2.74), we can hypothesize that the photoelectric signal could be propagated through the
paraxial rod filaments via charge transfer between rod proteins, modifying the pitch of its helix, which
in turn modifies the distribution of the mass of the rod along the axoneme. This leads to a change in
the motion wave running along the flagellum and eventually to a change in the swimming direction.
Chloroplasts
The photosynthetic compartment contains the pigments for absorbing light and channeling the
energy of the excited pigment molecules into a series of photochemical and enzymatic reactions.
These pigments are organized in proteic complexes embedded in the membrane of sac-like flat
compressed vesicles known as the thylakoids. These vesicles are about 24-nm thick and enclose a
space, termed lumen, 10-nm wide.
In prokaryotes, the thylakoids are free within the cytoplasm, whereas in eukaryotes they are
enclosed within bounding membranes to form the chloroplast. The colorless matrix of the chloroplast is known as the stroma. Inside the chloroplast, thylakoids are organized into two different
compartments, granal thylakoids, stacked into hollow disks termed grana, and stromal thylakoids
forming multiple connections between the grana. All thylakoids surfaces run parallel to the plane
of the maximum chloroplast cross-section. Chloroplasts contain nucleic acids and ribosomes. DNA
is naked, that is, not associated with proteins, and occurs in two configurations: scattered, but not
connected small nucleoids or as a peripheral ring. Chloroplasts are semiautonomous organelles that
replicate their own DNA, and this replication is not linked to the division of the organelle. Synthesis
of RNA and proteins is possible inside the chloroplast, though they are not strictly autonomous
from the nuclear genome. The plastid genes are transcribed and translated within the plastids. The
machinery of protein synthesis is, in any case, partially composed of imported nuclear gene products. In this respect, as in others, the chloroplast is no longer independent. Nevertheless, about
half of the plastid genome consists of genes that contribute to the machine of gene expression, for
example, genes for rRNA, tRNAs, RNA polymerase subunits, and ribosomal proteins. Plastids code
for, and synthesize some proteins that are components for photosystems, and particular subunits
of photosynthetic enzymes. The missing subunits of these complexes are coded in the nucleus and
must be imported from the cytoplasm.
Chloroplast development and division (self-replication) may be coordinated with that of the cell
or may proceed independently. They divide in mother cells and are inherited by daughter cells during vegetative division and usually only from the maternal side in sexual reproduction. The shape
and the number of chloroplasts are extremely variable from the single cup-shaped chloroplast of
Dunaliella salina, the ribbon-like chloroplast of Spirogyra, or stellate one of Zygnema to the numerous (about 10 8 ) ellipsoidal chloroplasts of Acetabularia giant cells.
The fact that algae of different divisions have different colors, due to the presence in the photosynthetic membrane system of a variety of pigments, might lead to the supposition that the photosynthetic membrane structures are variable. This is true since the features of photosynthetic
membrane system represent a diagnostic important element at the class level. In this chapter, we
will consider the structure, composition, and location of the photosynthetic membrane system in
each algal division.
Cyanobacteria
The photosynthetic apparatus of these algae is localized on intracytoplasmic membranes termed
thylakoids. The thylakoid membranes show considerable variations in structure and arrangements
Algae
As described above, changes in the motion trajectory by bending of the locomotory flagellum
are due to the screening of the photoreceptor by the eyespot that changes the electrostatic field. The
locomotory flagellum carries the paraxial rod (PAR; Figure 2.36a and b), a hollow rod-like structure
with a diameter of 90 nm along the entire length. The PAR is the true effector. When the photoreceptor is screened by the eyespot, the signaling state of the protein becomes the dominant isomer and a
change in the electrostatic field occurs. Since the photoreceptor and the paraxial rod are a structural
unit (Figure 2.74), we can hypothesize that the photoelectric signal could be propagated through the
paraxial rod filaments via charge transfer between rod proteins, modifying the pitch of its helix, which
in turn modifies the distribution of the mass of the rod along the axoneme. This leads to a change in
the motion wave running along the flagellum and eventually to a change in the swimming direction.
Chloroplasts
The photosynthetic compartment contains the pigments for absorbing light and channeling the
energy of the excited pigment molecules into a series of photochemical and enzymatic reactions.
These pigments are organized in proteic complexes embedded in the membrane of sac-like flat
compressed vesicles known as the thylakoids. These vesicles are about 24-nm thick and enclose a
space, termed lumen, 10-nm wide.
In prokaryotes, the thylakoids are free within the cytoplasm, whereas in eukaryotes they are
enclosed within bounding membranes to form the chloroplast. The colorless matrix of the chloroplast is known as the stroma. Inside the chloroplast, thylakoids are organized into two different
compartments, granal thylakoids, stacked into hollow disks termed grana, and stromal thylakoids
forming multiple connections between the grana. All thylakoids surfaces run parallel to the plane
of the maximum chloroplast cross-section. Chloroplasts contain nucleic acids and ribosomes. DNA
is naked, that is, not associated with proteins, and occurs in two configurations: scattered, but not
connected small nucleoids or as a peripheral ring. Chloroplasts are semiautonomous organelles that
replicate their own DNA, and this replication is not linked to the division of the organelle. Synthesis
of RNA and proteins is possible inside the chloroplast, though they are not strictly autonomous
from the nuclear genome. The plastid genes are transcribed and translated within the plastids. The
machinery of protein synthesis is, in any case, partially composed of imported nuclear gene products. In this respect, as in others, the chloroplast is no longer independent. Nevertheless, about
half of the plastid genome consists of genes that contribute to the machine of gene expression, for
example, genes for rRNA, tRNAs, RNA polymerase subunits, and ribosomal proteins. Plastids code
for, and synthesize some proteins that are components for photosystems, and particular subunits
of photosynthetic enzymes. The missing subunits of these complexes are coded in the nucleus and
must be imported from the cytoplasm.
Chloroplast development and division (self-replication) may be coordinated with that of the cell
or may proceed independently. They divide in mother cells and are inherited by daughter cells during vegetative division and usually only from the maternal side in sexual reproduction. The shape
and the number of chloroplasts are extremely variable from the single cup-shaped chloroplast of
Dunaliella salina, the ribbon-like chloroplast of Spirogyra, or stellate one of Zygnema to the numerous (about 10 8 ) ellipsoidal chloroplasts of Acetabularia giant cells.
The fact that algae of different divisions have different colors, due to the presence in the photosynthetic membrane system of a variety of pigments, might lead to the supposition that the photosynthetic membrane structures are variable. This is true since the features of photosynthetic
membrane system represent a diagnostic important element at the class level. In this chapter, we
will consider the structure, composition, and location of the photosynthetic membrane system in
each algal division.
Cyanobacteria
The photosynthetic apparatus of these algae is localized on intracytoplasmic membranes termed
thylakoids. The thylakoid membranes show considerable variations in structure and arrangements