Bacterial Cell Structure, Types, and Reproduction
1. The Bacterial Cell (Prokaryote)
Most importantly, bacterial cells have no nucleus and are smaller and more primitive than Eukaryotic cells. They have no cells or tissues, or higher organizations.
It has 3 parts:
The Shell
A bacterium can have 3 envelopes:
- Capsule: The outermost envelope of bacteria, with variable sizes depending on the species. It has a mucous appearance and functions to provide resistance to environmental dryness. This wrapper does not appear in all species.
- Bacterial Wall: Found beneath the capsule, it is a very sturdy structure. Its function is to give the cell its shape.
- Cell membrane: It is very similar to eukaryotic cells. It has inward folds called Mesosomes. These Mesosomes extend the membrane surface and have different functions associated with them, such as cellular respiration or photosynthesis in autotrophic bacteria.
Cytoplasm
- Ribosomes: They are smaller and more abundant than in eukaryotic cells. Their function is the synthesis of proteins.
- DNA: As prokaryotes, bacteria have their DNA directly in the central cytoplasm. Other independent, smaller DNA fragments are called Plasmids.
- Inclusions: Small vacuoles or vesicles with different functions. Their function depends on their content: they can contain reserves of energy, inorganic matter, gas, etc.
Appendices
There are 2 types:
- Flagella: These structures may reach 10 times the size of the bacteria.
- Fimbriae or Pili: These are very small, short, numerous, and rigid structures.
They are classified according to function:
- Fimbriae of infection: These are typical of other cells. They allow attachment to infected cells.
- Sex Fimbriae: Responsible for facilitating the transfer of genetic material from one bacterium to another.
2. Forms of Bacteria
- Cocci: Spherical-shaped bacteria.
- Bacilli: Rod-shaped bacteria.
- Spirilla: Spiral-shaped bacteria.
- Vibrio: Comma-shaped bacteria.
3. Properties of Stain
The Gram stain is a type of staining used to visualize bacteria and the properties of the bacterial wall.
There are 2 types:
- Gram-Positive Bacteria: Stained bright pink.
- Gram-Negative Bacteria: Stained pale pink.
According to the shape and staining, we can refer to: Gram-positive cocci, Gram-negative bacilli, etc.
4. Bacterial Classification and Nomenclature
The large number of species and the physiological diversity of bacteria make classification very complicated.
They are classified according to staining properties, among other characteristics.
Bacteria belong to the kingdom Monera. Organisms are divided into orders, families, genera, and species.
To name a species, the genus is written first with an initial capital letter, followed by the species name in lowercase. The scientific name must be written in italics, or underlined when writing by hand.
The scientific name is written in Latin.
5. Mechanism of Reproduction
Bacteria reproduce by cell division. The cycle has 2 phases:
- Active Phase: This phase begins with DNA replication. The DNA is attached to the Mesosome to help with its separation to the sides of the bacteria. An invagination occurs in the central part of the bacteria, eventually producing separation into 2 cells. These 2 bacteria formed are identical to the original in terms of genetic material, but smaller.
- Resting Phase: The phase of growth of the new bacteria to the size of the original bacterium.
Cell division can take from 20 minutes to 1 hour.
All bacteria descended from the same original bacterium form a colony.