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Prokaryote
A prokaryote is a single-celledorganism that lacks a membrane-boundnucleus (karyon), mitochondria, or any othermembrane-bound organelle. All theintracellular water-soluble components(proteins, DNA and metabolites) are locatedtogether in the same volume enclosed by thecell membrane, rather than in separate cellularcompartments. Prokaryotes, however, dopossess protein-based microcompartments,which are thought to act as primitiveorganelles (protein-bounded and lipid-bounded organelles). Some prokaryotes alsohave multicellular stages in their life cycles,such as myxobacteria, or create large colonies,like cyanobacteria
Fig. 1
Capsule - Found in some bacterial cells, this additional outer
covering protects the cell when it is engulfed by other
organisms, assists in retaining moisture, and helps the cell
adhere to surfaces and nutrients.
Cell Wall - Outer covering of most cells that protects the
bacterial cell and gives it shape.
Cytoplasm - A gel-like substance composed mainly of water that
also contains enzymes, salts, cell components, and various
organic molecules.
Cell Membrane or Plasma Membrane - Surrounds the cell's
cytoplasm and regulates the flow of substances in and out of
the cell.
• Pili - Hair-like structures on the surface of the cell
that attach to other bacterial cells. Shorter pili called
fimbriae help bacteria attach to surfaces.
Flagella - Long, whip-like protrusion that aids in
cellular locomotion.
Ribosomes - Cell structures responsible for protein
production.
Plasmids - Gene carrying, circular DNA structures
that are not involved in reproduction.
Nucleiod Region - Area of the cytoplasm that
contains the single bacterial DNA molecule.
Most prokaryotes reproduce asexually through a
process called binary fission. During binary fission,
the single DNA molecule replicates and the original
cell is divided into two identical cells.
Binary fission begins with the single DNA molecule
replicating and both copies attaching to the cell
membrane.
Next, the cell membrane begins to grow between the
two DNA molecules. Once the bacterium just about
doubles its original size, the cell membrane begins
to pinch inward.
A cell wall then forms between the two DNA
molecules dividing the original cell into two
identical daughter cells.
Reproduction in bacteria
Fig. 3
Reproduction
• When conditions are favourable bacteria can reproduce every 20 minutes
• In 48 hours a single bacterial cell could become culture 4000 times the mass of the earth
• Thankfully the food supply is limited and this does not happen
Binary Fission
• When a cell has almost doubled in size it will replicate its DNA and divide in half
• This produces 2 identical daughter cells
• Binary fission is a form of asexual reproduction
• Asexual reproduction does not invovle the exchange of genetic material
Conjugation
• Is a form of sexual reproduciton
• Genetic Information is exchanged between individuals
• A long bridge of proteins forms between two bacterial cells
• DNA is transferred from one cell (donor) to another (recipient)
1- Donor cell produces
pilus. 2- Pilus attaches to
recipient cell and brings
the two cells together.
3- The mobile plasmid is
nicked and a single strand
of DNA is then
transferred to the recipient
cell.
4- Both cells synthesize a
complementary strand to
produce a double stranded
circular plasmid and also
reproduce pili; both cells
are now viable donors.
Fig. 4
Spore Formation
• Bacteria form spores during unfavourableconditions
• One type is called an endospore
– Cell forms a thick internal wall the encloses its DNA
• Spores can remain dormant for months until conditions improve
Morphology of bacterial cellCoccus (plural cocci or coccuses) can
be used to describe any bacterium that
has a spherical shape. It is one of the
three distinct types of bacteria shapes,
the other two being bacillus (rod-
shaped) and spirillum (spiral-shaped)
cells
Spirochaetes (also spelled spirochetes)belong to a phylum of distinctivediderm (double-membrane) bacteria,most of which have long, helicallycoiled (corkscrew-shaped) cells.Spirochaetes are chemoheterotrophicin nature, with lengths between 5 and250 µm and diameters around 0.1–0.6 µm
Fig. 7
Fig. 8
Vibrio is a genus of Gram-negativebacteria possessing a curved-rod shape(comma shape), several species ofwhich can cause foodborne infection,usually associated with eatingundercooked seafood. Typically foundin saltwater, Vibrio species arefacultative anaerobes that test positivefor oxidase and do not form spores. Allmembers of the genus are motile andhave polar flagella with sheaths.
Fig. 9
Reference
Books
Plant Pathology by G N Agrios
Web Sources
http://agridr.in/tnauEAgri/eagri50/PATH171/index.html
http:// agriinfo.com
http:// wekipedia.org
Image References
Fig.1 http://en.wikipedia.org/wiki/Bacterial_cell_structure
Fig-2 http://micro.magnet.fsu.edu/cells/bacteriacell.html
Fig-3 http://media-1.web.britannica.com/eb-media//93/130893-050-5B4B3040.jpg
Fig-4 http://upload.wikimedia.org/wikipedia/commons/thumb/3/3e/Conjugation.svg/2000px-Conjugation.svg.png
Fig-5 http://images.tutorvista.com/content/cell-structure/prokaryote-and-eukaryote-cell.jpeg
Fig-6 http://3.bp.blogspot.com/-LYYiLl2sLQU/Ux34riE3DvI/AAAAAAAABy4/7LoImQQpflI/s1600/gram-bacteria1-copy.png
Fig-7http://en.wikipedia.org/wiki/Bacterial_cellular_morphologies#mediaviewer/File:Bacterial_morphology_diagram.svg
Fig-8http://upload.wikimedia.org/wikipedia/commons/thumb/6/69/Bacterial_morphology_diagram.svg/2000px-Bacterial_morphology_diagram.svg.png
Fig-9
http://upload.wikimedia.org/wikipedia/commons/thumb/d/db/Vibrio_cholerae_01.jpg/240px-Vibrio_cholerae_01.jpg