TD °1: Introduction to cell biology
1- Definition of cell biology :
Cell biology (formerly known as cytology) is a discipline of biology that studies cells, both structurally
and functionally, as well as the mechanisms that enable their survival.
2- Definition of the cell :
The cell is the basic structural and functional unit of any living being, capable of living in isolation and
reproducing.
3- History of Cell Biology :
Cells cannot be observed with the naked eye because of their very small size. The history of cell
biology is therefore closely linked to the invention of microscopes. The first compound microscopes
were developed at the end of the sixteenth century, which stimulated research into microscopic
objects. The history of cell biology can be summarized as follows:
Robert Hooke(1665)
First coined the term cell (small chamber) while observing cork sections with a rudimentary singlelens microscope (actually dead plant cells).
Figure 1: Robert Hooke cork cells and Robert Hooke microscope
Antony Van Leeuwenhoek (1674)
Known for his improvements to the microscope, describes several living micro-organisms (protists,
bacteria, etc.).
Matthias Schleiden(1838)
German botanist used microscopes to study plants. He came to realize that all the plants he observed
were made up of cells.
Theodore Schwann(1839)
German zoologist who, after observing numerous animal organisms, concluded that all animals are
also made of cells.
Rudolf Virchow(1858)
German physician, asserts that cells arise from the result of cell division "omnis cellula ex cellula".
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3- Foundation of cell theory:
The observations and discoveries of these scientists led to the establishment of the cell theory, which
comprises three main principles:
- All living beings are composed of one or more cells.
- The cell is the basic unit of life.
- Every cell originates from another cell through cell division.
4-cell classification :
Cells are divided into three main categories according to their structure: prokaryotes (bacteria)
eukaryotes (animal or plant cells) and acaryotes (viruses).
Living organisms
Acellulaires
cellulaies
les protistes inferieurs
Les virus
Protiste supérieur (eucaryotes)
organismes supérieurs
Protiste inferieur ( procaryotes)
-Algues
-Algues bleu-verts : cyanophycées
-Protozoaires
- eubactéries
animaux
végétaux
-Champignons
Bactéries non photosynthétique
Pseudomonas
Eutérobacteries
Bactéries photosynthétique
particulière : Sprirochétes
Archeobacteries …etc
Diagram; classification of living organisms
4-1-Prokaryotic cells
Prokaryotic cells (from the ancient Greek pro= primitive; caryon = nucleus) mean cells without a true
nucleus, i.e. the genetic material is not enclosed in a nuclear envelope. The prokaryotic cell has a
simple ultrastructure due to the absence of intracellular organelles. Prokaryotes are essentially
unicellular organisms, mainly bacteria.
4-2- Eukaryotic cells
Eukaryotic cells (eu = true, caryon = nucleus) have a nucleus delimited by a nuclear envelope
containing the genetic material. Their cytoplasm is highly structured, containing an endomembrane
system and organelles. Eukaryotic cells make up almost all multicellular organisms.
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4-3- Characteristics of prokaryotic and eukaryotic cells
All cells, whether eukaryotic or prokaryotic, have four key components in common:
- Plasma membrane
- Cytoplasm
- DNA
- Ribosomes
Despite these similarities, prokaryotes and eukaryotes differ in a number of respects
5-Methods for studying the cell :
1-Optical microscope:
Antony Van Leeuwenhoek (1674) is considered the first inventor of the
microscope.
Simple optics (with a single lens)
A series of lenses associated with a light source.
There are several types (light-focus, dark-focus, phase-contrast, etc.).
Microscopic study may involve a dead cell (MO with clear food, darkfield) or a living cell
(MO with phase contrast).
(MO with phase contrast)
The same study can be cytological (when the sample is a needle puncture, a biological fluid
biological fluid) or histological (when the sample is a biopsy, operative or necropsy
necropsy)
*Steps in processing a sample for MO study:
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Fixation (with 10% formalin)
Dehydration (ascending alcohols)
Kerosene embedding
Microtome sectioning (05 microns thick)
Staining (HES or special)
Mounting using transparent sticky liquid between slide and coverslip
2-Electron microscope :
More recent technique for observing cells (1930) based on deviation of an electron beam
electromagnetic lenses in the form of coils (instead of lenses made of transparent media).
transparent media: glass).
There are 02 types:
-Transmission electron microscope (TEM): gives 2D black-and-white images
-Scanning electron microscope (SEM): gives 3D black-and-white images.
*Steps in processing a sample for TEM study:
Fixation (with 10% formalin or osmium tetraoxide)
Dehydration (ascending alcohols)
Epoxy resin embedding
Ultramicrotome sectioning (50 nanometre thickness)
Staining (using electron-opaque heavy metal salts)
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