What Are Cilia and
Flagella
Cilia and
flagella are burrs from some cells that assist in cellular locomotion. They are
formed from specialized groupings of microtubules known as basal bodies.
If the
protrusions are small and several they are called cilia. If they are longer and
less numerous (usually only one or two) they are called flagella.
Some Identifying
Features:
Typically cilia
and flagella have a core consisting of microtubules linked to the plasma
membrane arranged in what is known as a 9 + 2 pattern.
The pattern is so
named since a ring of nine microtubule "doubles" has in its center
two singular microtubules.
This organization
allows the slipping of the microtubule doubles against one another to
"bend" the cilia or flagella. This type of organization is found in
most eukaryotic cilia and flagella
A flagellum is a
whip-like tail; usually cells only have one, occasionally two, and help the
cell to move. Cilia and flagellum are only found on animal cells and not all
animal cells have them.
Cilia are minor
whips like structures that cover a cell and help it to move, move liquid that
is all over it or to clean something.
Where can cilia
and flagella are found
Both cilia and
flagella are found in numerous types of cells. For example, the sperm of many
animals, algae, and even ferns have flagella.
Cilia can be
found in areas such as the respiratory and female reproductive tracts.
Movements of
Flagella and Cilia
Strictly speaking
are the cilia and flagellar movements of eucaryotes intracellular movements;
for although a flagellum (or a cilium) appears to be an appendage of the cell,
is it encircled by the plasma membrane. All dynein molecules along the whole
length of the microtubule have continuously to be supplied with adequate
volumes of ATP. Both ion milieu and pH of their surrounding has to be right.
P. SATIR (1968,
1976 at that time at the University of California, Berkeley) defined the
process of movement as a sliding filament mechanism where the peripheral
tubuline doublets slide past each other. In the course of this contacts the
dynein that is always anchored to the A tubule the B tubule of the neighboring
doublet with its tips.
This mechanism
describes the forward and backward swings of the cilium but not the numerous
modifications of cilia movements found mainly with protozoa. There exist
pulling and pushing flagella, as well as tinsel-type flagella. There exist
flagella that move around an imaginary axis and flexible flagella where the
movement spreads wave-like along the axis. Many motile cells can switch into
forward or backward gear or can bring out additional or a less strong
improvements of the course.
Cilia differ from
flagella only in their number per cell. They are usually quite short and cover
often the whole surface of a cell. Cilia are rare in plants, an often cited
example are the zoospores of Vaucheria sessilis.
With algae
(except red algae) are flagellated stages common. They are often found with the
spermatozoids (male germ cells) of mosses and ferns. Early during the evolution
of seed plants were flagellated stages more and more driven out. Among the few
still existing exceptions are the spermatozoids of Gingko biloba and the cycads.
Movements are
often controlled by extern indicators. Many protists are attracted by specific
resources of pleasure called taxis: light (phototactic behaviour) or certain
chemicals (chemotactic behaviour). Normally comes after the movement a
concentration or intensity gradient. If a threshold of sensation is passed,
begins a backward response. During the last generations was signal recognition
a much-studied topic. We know, for example, that the carotenoids within the
stigma of some algae (Euglena, for example) are very sensitive to blue light.
The chloroplast movements of the alga Mougeotia are managed by thephytochrome
system and germ cells (of algae) respond to varieties certain sexual
attractants. But how the perceived signal is transformed and how signals of the
same or the opposite kind are co-ordinated in a guided motion is not even
basically understood.
The basis of many
flagella is outfitted with a complexly structured basal body. M. MELKONIAN
(Botanisches Institut der Universität Köln) examined the basal bodies of a
number of algae and found group-specific patterns. He ranked these structures
and their differences as features that help to understand the family
relationships of the single groups of algae significantly.
Types of cilia
and flagella
There two types
of cilia: motile and non-motile or primary cilia:
A. Non-motile
or primary cilia are found in nearly every cell in all mammals and as
the name suggests these do not beat. They can be found in human sensory organs
such as the eye and the nose.
B. Motile
cilia are found on the surface of cells and they beat in a rhythmic manner.
They can be found in the lining of the trachea (windpipe), where they sweep
mucus and dirt out of the lungs. In female mammals, the beating of cilia in the
fallopian tubes moves the ovum from the ovary to the uterus.
There are three
types of flagella: bacterial, archaeal and eukaryotic:
A. Bacterial
flagella are helical filaments that rotate like screws. They are found in E.
coli, Salmonella typhimurium. There may be one, two or many such flagella per
cell. These flagella provide motility to bacteria.
B. Archaeal
flagella are similar to bacterial flagella but they have a unique structure
which lacks a central channel.
C. Eukaryotic
flagella are complex cellular projections that lash back and forth. (e.g., the
sperm cell, which uses its flagellum to move itself through the female
reproductive tract.
Diseases:
Lack of proper
functioning of cilia and flagella can cause several problems in human beings,
For example:
If the cilia in
the fallopian tubes are not functioning properly then the fertilized ovum will
not reach the uterus and thus result in ectopic pregnancy.
A defect of the
main cilium in the renal tube cells can lead to polycystic kidney disease.
Flagellum
dysfunction can also be responsible for male infertility because the sperm is
not motile and cannot swim to the ovum.
