The word cell is derived from the Latin word cella,
which meaning "small room. The cell is the basic structural, functional, and
biological unit of all known organisms. A cell is the smallest unit
of life. Cells are often called the "building blocks of life".
The study of cells is called cell biology, cellular biology, or cytology.
It can
also be said that the cell is a complete unit of metabolism because it has all
the chemical and physical factors necessary for its growth and maintenance. An
isolated cell is also capable of growth and differentiation in a laboratory if
the proper nutrients and appropriate environments are given.The cell is the smallest unit of matter
that can carry on all the processes of life.
History of Cell
The cell
theory, or cell doctrine, states that all organisms are composed of similar
units of organization, called cells. The concept was formally articulated in
1839 by Schleiden & Schwann and has remained as the foundation of modern
biology. The idea predates other great paradigms of biology including Darwin’s
theory of evolution (1859), Mendel’s laws of inheritance (1865), and the
establishment of comparative biochemistry (1940).
First Cells observed
in the history
The cell was first
discovered and named by Robert Hooke in
1665. He remarked that it looked strangely similar to cellula or small rooms
which monks inhabited, thus deriving the name. However what Hooke actually saw
was the dead cell walls of plant cells (cork) as it appeared under the
microscope. Hooke’s description of these cells was published in Micrographia.
The cell walls observed by Hooke gave no indication of the nucleus and other
organelles found in most living cells. The first man to witness a live cell under
a microscope was Anton van
Leeuwenhoek, who in 1674 described the algae Spirogyra. Van
Leeuwenhoek probably also saw bacteria.
Formulation of the
Cell Theory
In 1838, Theodor
Schwann and Matthias Schleiden were enjoying after-dinner coffee and talking
about their studies on cells. It has been suggested that when Schwann heard
Schleiden describe plant cells with nuclei, he was struck by the similarity of
these plant cells to cells he had observed in animal tissues. The two
scientists went immediately to Schwann’s lab to look at his slides. Schwann
published his book on animal and plant cells (Schwann 1839) the next year, a
treatise devoid of acknowledgments of anyone else’s contribution, including
that of Schleiden (1838). He summarized his observations into three conclusions
about cells:
1. The cell is the unit of structure, physiology,
and organization in living things.
2. The cell retains a dual existence as a
distinct entity and a building block in the construction of organisms.
3. Cells form by free-cell formation, similar to
the formation of crystals (spontaneous generation).
We know today that the
first two tenets are correct, but the third is clearly wrong. The correct
interpretation of cell formation by division was finally promoted by others and
formally enunciated in Rudolph Virchow’s powerful dictum, Omnis cellula
e cellula,: “All cells only arise from pre-existing cells”.
Modern Cell Theory
1. All known living things are made up of cells.
2. The cell is structural & functional unit
of all living things.
3. All cells come from pre-existing cells by
division. (Spontaneous Generation does not occur).
4. Cells contains hereditary information which is
passed from cell to cell during cell division.
5. All cells are basically the same in chemical
composition.
6. All energy flow (metabolism &
biochemistry) of life occurs within cells.
As with the rapid growth of
molecular biology in the mid-20th century, cell biology research
exploded in the 1950’s. It became possible to maintain, grow, and manipulate
cells outside of living organisms. The first continuous cell line to be so
cultured was in 1951 by George Otto Gey and coworkers, derived from cervical
cancer cells taken from Henrietta Lacks, who died from her cancer in 1951. The
cell line, which was eventually referred to as HeLa cells, have been the watershed in
studying cell biology in the way that the structure of DNA was the significant
breakthrough of molecular biology.
In an avalanche of
progress in the study of cells, the coming decade included the characterization
of the minimal media requirements for cells and development of sterile cell
culture techniques. It was also aided by the prior advances in electron
microscopy, and later advances such as development of transfection methods, discovery
of green fluorescent protein in jellyfish, and discovery of small interfering
RNA (siRNA), among others.
A outline history of
cell:
1595 – Jansen credited with 1st compound
microscope
1655 – Hooke described ‘cells’ in cork.
1674 – Leeuwenhoek discovered protozoa. He saw bacteria some 9 years later.
1833 – Brown descibed the cell nucleus in cells of the orchid.
1838 – Schleiden and Schwann proposed cell theory.
1840 – Albrecht von Roelliker realized that sperm cells and egg cells are also cells.
1856 – N. Pringsheim observed how a sperm cell penetrated an egg cell.
1858 – Rudolf Virchow (physician, pathologist and anthropologist) expounds his famous conclusion: omnis cellula e cellula, that is cells develop only from existing cells [cells come from preexisting cells]
1857 – Kolliker described mitochondria.
1879 – Flemming described chromosome behavior during mitosis.
1883 – Germ cells are haploid, chromosome theory of heredity.
1898 – Golgi described the golgi apparatus.
1938 – Behrens used differential centrifugation to separate nuclei from cytoplasm.
1939 – Siemens produced the first commercial transmission electron microscope.
1952 – Gey and coworkers established a continuous human cell line.
1955 – Eagle systematically defined the nutritional needs of animal cells in culture.
1957 – Meselson, Stahl and Vinograd developed density gradient centrifugation in cesium chloride solutions for separating nucleic acids.
1965 – Ham introduced a defined serum-free medium. Cambridge Instruments produced the first commercial scanning electron microscope.
1655 – Hooke described ‘cells’ in cork.
1674 – Leeuwenhoek discovered protozoa. He saw bacteria some 9 years later.
1833 – Brown descibed the cell nucleus in cells of the orchid.
1838 – Schleiden and Schwann proposed cell theory.
1840 – Albrecht von Roelliker realized that sperm cells and egg cells are also cells.
1856 – N. Pringsheim observed how a sperm cell penetrated an egg cell.
1858 – Rudolf Virchow (physician, pathologist and anthropologist) expounds his famous conclusion: omnis cellula e cellula, that is cells develop only from existing cells [cells come from preexisting cells]
1857 – Kolliker described mitochondria.
1879 – Flemming described chromosome behavior during mitosis.
1883 – Germ cells are haploid, chromosome theory of heredity.
1898 – Golgi described the golgi apparatus.
1938 – Behrens used differential centrifugation to separate nuclei from cytoplasm.
1939 – Siemens produced the first commercial transmission electron microscope.
1952 – Gey and coworkers established a continuous human cell line.
1955 – Eagle systematically defined the nutritional needs of animal cells in culture.
1957 – Meselson, Stahl and Vinograd developed density gradient centrifugation in cesium chloride solutions for separating nucleic acids.
1965 – Ham introduced a defined serum-free medium. Cambridge Instruments produced the first commercial scanning electron microscope.
Types of cells:
The organisms may have two types of cells, viz., prokaryotic cells and
eukaryotic cells:
Prokaryotic
Cells:
The prokaryotic cells
also lack in well defined cytoplasmic organelles. The prokaryotic cells occur
in viruses, bacteria and blue green algae.
Eukaryotic
Cells:
The eukaryotic (Gr.,
eu = good or well; karyotic = nucleus) cells are the true cells which occur in
the plants (from algae to angiosperms) and the animals (from Protozoa to
mammals).
Though the eukaryotic
cells have different shape, size, and physiology but all the cells typically
composed of plasma membrane, cytoplasm and its organelles, viz., mitochondria,
endoplasmic reticulum, ribosomes, Golgi apparatus, etc., and a true nucleus. Here
the nuclear contents such as DNA, RNA and nucleoproteins remain concentrated
and separated from the cytoplasm by the thin, perforated nuclear membranes.
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Prokaryotes. Newnes. Apr
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Campbell Biology—Concepts and Connections.
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^ D. Peter Snustad, Michael J. Simmons, Principles
of Genetics – 5th Ed. (DNA repair mechanisms) pp. 364-368
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Ananthakrishnan R, Ehrlicher A. "The Forces Behind Cell Movement".
Biolsci.org. Retrieved 2009-04-17.
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Alberts, Bruce (2002). Molecular biology
of the cell (4th ed.). Garland Science. pp. 973–975. ISBN 0815340729.
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Ananthakrishnan R, Ehrlicher A (June
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Basic Biology