CELL BIOLOGY, HISTORY AND CELLULAR THEORY
In this article, we shall learn the definition of cell biology, history of and cellular theory.
Cell biology is generally is the study of cells. It is not just a simple term, but also a broader field which covers many branches of biology. Cell biology is also known as “Cytology”. Cell biology includes the following departments;
- Cell structure
- Cell functions
- Molecular organization of cell
- Growth of cell
- Cell division
First of all, we differentiate some features of plant and animal cell:
Features Plant cell Animal cell
Cell wall Present Absent
Plastids Present Absent
Glyoxisomes Present Absent
Centrioles absent Present
Flagella absent Present
Lysosomes absent Present
Shape Fixed not fixed
Position of vacuoles Larger (central) Smaller(one or more than one)
Position of nucleus Peripheral Central
Food storage Starch Glycogen
Photosynthesis occurs doesn’t occur
Now we discuss some similarities between animal and plant cells,
Both animal and plant cells are eukaryotic as they contain a prominent nucleus. Animal and plant cells have cell membranes and cytoplasm. They contain organelles like ribosomes, endoplasmic reticulum, Golgi complex, peroxisomes, and mitochondria, etc.
Now we discuss the history of cell;
History of cell
As we know that all life is made of cells. A living cell is discovered in 1600 at the time of the invention of the microscope.
Robert Hook discovered cork (dead Tree Bark) in 1665. Corks are dead cells. That’s why they looked empty when they first examined under a microscope. Robert saw empty boxes in the cork and named those boxes “Cell”. Robert Hooke also discovered the cell wall in the cork, but the cell wall gave no indication of the nucleus and other organelles that we find today in most living cells. After a few years later, the first living cells were observed by Dutch naturalist Anton Van Leeuwenhoek. In 1674 he described algae spirogyra. Van Leeuwenhoek also saw some bacteria under a microscope. For one and a half-century later, the general significance of the cell was not appreciated by biologists. However, in 1809, Lamarck suggested that nobody can have a life if its parts are not cellular tissues or are not composed of cellular tissues. In 1831, an English botanist Robert Brown discovered the nucleus in the eukaryotic cell. In 1838 a German botanist Matthias Schleiden examined plant tissues and suggested the first statement of cell theory. He stated that all plants are produced from individual cells which are completely independent. One year later, in 1839, German zoologist Theodor Schwann demonstrated that all animal tissues also consist of individual cells. Thus, two scientists, Schleiden and Schwann presented the cell in its initial form. We can summarize the discoveries of some scientists as follow;
- 1595- Jansen made 1st compound microscope.
- 1655- Hooke discovered dead cells in cork.
- 1674- Leeuwenhoek discovered protozoa. He also examined some bacteria about 9 years later.
- 1831- Robert Brown described the nucleus in the cells of the orchid.
- 1838- Two German scientists Schleiden and Schwann proposed cell theory.
- 1840- Von Reolliker realized that gametes (sperm & egg) are also cells.
- 1856- Pringsheim examined how a sperm cell penetrated an egg cell.
- 1857- Kolliker discovered mitochondria in the cell.
- 1858- Rudolf Virchow, a German physician presented an important broader concept of the cell theory. He stated that all living cells originate from pre-existing cells (“Omnis cellula e cellula).
- 1862- Louis Pasteur gave experimental proof of the concept of the cell theory given by Rudolf Virchow.
- 1879- Flemming described chromosomal behavior during mitosis.
- 1898- Golgi described the Golgi complex.
- 1938- Behrens applied differential centrifugation to separate nuclei from the cytoplasm.
- 1939- Seimens produced the first commercial Transmission electron microscope.
- 1957- Meselson and Stahl developed density gradient centrifugation in cesium chloride solutions for separating nucleic acids.
- 1965- Ham introduced a first defined serum-free medium.
- 1976- Sota and coworkers published papers showing that different cell lines require different mixtures of hormones and growth factors in serum-free media.
- 1981- Transgenic mice and fruit flies are produced. Mouse embryonic stem cell line established.
- 1995- Tsien identified a mutant of GFP with advanced spectral properties.
- 1999- Hamilton and Baulcombe discovered siRNA as part of post-transcriptional genes silencing (PTGS) in plants.
The basic definition of cell theory is that “all living things are made of one or more cells. The cell is the basic functional and structural unit of life. Not a single living organism (unicellular or multicellular) lack the basic unit of life i.e. the cell. New cells arise from pre-existing cells. Rudolf Virchow made significant contributions to this theory as,” cell is the basic functions as well as a structural unit of life.
Formulation of cell theory
In 1838 Theodor Schwann and Matthias Schleiden were talking about their study on cells after taking dinner-coffee. It is proposed that Schwann heard while Schleiden was describing plant cells with nuclei, he was struck by the similarity of these plant cells to cells that he had observed in the animal tissues. The two scientists went quickly to Schwann’s lab to look at his slides. After one year later Schwann published his book on plant and animal cells (1839), a treatise devoid of acknowledgment of anyone else’s contribution including that of Schleiden (1838). He summarized his observations into three results about cell which are described below,
- The cell is the unit of structure, function, and organization of the living cells.
- The cell retains a dual existence as a distinct entity and a building block in the construction of living things.
- Cells are formed from free cell formation, which is similar to the formation of crystals (spontaneous generation).
Today we know that the first two tenets are correct, but a third is absolutely incorrect. “Omnis cellula e cellula. All cells only arise from pre-existing cells.
The Modern Tenets of cell theory include:
- All living things are made up of cells.
- The cell is the structural and functional unit of life.
- New cells arise from pre-existing cells by cell division.
- Cells contain hereditary information which is passed from one cell to another by cell division.
- All cells are similar in chemical composition.
- All energy flow (metabolism) of life occurs within the cell.