1. Cell Wall: Prokaryotic cells, both bacteria and archaea, have a rigid cell wall
that surrounds the cell membrane. The cell wall provides structural support
and protection to the cell. The composition of the cell wall varies between
bacteria and archaea.
2. Cell Membrane: Like eukaryotic cells, prokaryotic cells have a cell membrane
(plasma membrane) that encloses the cytoplasm and separates the interior of
the cell from its external environment. The cell membrane regulates the
passage of substances in and out of the cell.
3. Cytoplasm: The cytoplasm is the gel-like substance within the cell membrane
where various cellular processes occur. It contains enzymes, molecules, and
cellular structures involved in metabolism.
4. Nucleoid Region: Prokaryotic cells lack a true nucleus that is enclosed by a
membrane. Instead, they have a nucleoid region where the cell's genetic
material, typically a single, circular DNA molecule, is located. The DNA is not
enclosed in a nucleus, but it is concentrated in this region.
5. Ribosomes: Prokaryotic cells contain ribosomes, which are responsible for
protein synthesis. These ribosomes are smaller than those found in eukaryotic
cells.
6. Flagella: Many prokaryotic cells possess flagella, whip-like appendages that
allow the cell to move. Flagella are used for locomotion and are often critical
for bacteria to reach nutrients or escape from harmful substances.
7. Pili (Fimbriae): Pili are hair-like structures that protrude from the cell surface.
They can serve various functions, including adhesion to surfaces or other cells
and the transfer of genetic material during conjugation in bacteria.
8. Plasmids: Some prokaryotes contain small, circular pieces of DNA called
plasmids. Plasmids often carry genes that provide the cell with additional
capabilities, such as antibiotic resistance.
9. Inclusions: Prokaryotic cells may contain inclusion bodies, which are storage
structures that store nutrients or other substances needed by the cell.
10. Capsule: Some bacteria have a capsule, a protective layer of polysaccharides
or proteins that surrounds the cell wall. The capsule can protect the bacterium
from the host's immune system and help it adhere to surfaces.
11.
1. Spherical: These bacteria are round or spherical in shape.
Examples include Streptococcus and Staphylococcus.
12. Bacillus (plural: bacilli):
1. Rod-shaped: Bacilli are elongated, cylindrical bacteria.
Examples include Escherichia coli (E. coli) and Bacillus anthracis
(causing anthrax).
13. Spirillum (plural: spirilla):
1. Spiral-shaped: Spirilla are spiral or helical-shaped bacteria.
They may have one or more twists. Examples include
Helicobacter pylori and Spirillum.
14. Spirochete:
1. Corkscrew-shaped: Spirochetes are long, thin, and tightly
coiled bacteria. Examples include Treponema pallidum (causing
syphilis) and Borrelia burgdorferi (causing Lyme disease).
15. Vibrio:
1. Comma-shaped: Vibrio bacteria are curved or comma-shaped.
Vibrio cholerae, the causative agent of cholera, is an example.
16. Coccobacillus (plural: coccobacilli):
1. Oval or short rod-shaped: These bacteria have an
intermediate shape between cocci and bacilli. Bordetella
pertussis, causing whooping cough, is an example.
17. Filamentous:
1. Thread-like: Some bacteria grow in long, thin filaments.
Examples include Actinomyces.
18. Pleomorphic:
1. Variable shape: Pleomorphic bacteria lack a defined shape and
can take on various forms. Mycoplasma is an example of
pleomorphic bacteria.
19. Stalked:
1. Stalked or appendaged: These bacteria have a stalk-like
structure that extends from one end of the cell. Caulobacter is
an example.
20. Square:
1. Square-shaped: Very rare in nature, some bacteria have a
square shape. Haloquadratum walsbyi is an example.
It's important to note that bacterial shape can be influenced by various
factors, including the presence of cell wall structures like peptidoglycan,
environmental conditions, and the growth stage of the bacterium.
Additionally, bacterial species can exhibit a range of sizes, from microscopic
to visible with the naked eye.
Understanding bacterial shapes is valuable not only for classification but
also for studying their physiology, ecology, and pathogenesis. Different
shapes may have specific advantages or adaptations related to their
environments and lifestyles.