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Cholera as a prokaryote
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Introduction
This presentation focuses on:
• The cholera bacterium as an
example of a prokaryotic
organism.
• How the cholera bacteria produce
toxins which increase secretion of
chloride ions into the lumen of the
intestine, resulting in severe
diahorrea.
• The use of oral rehydration
solutions (ORS) in the treatment
of diarrhoeal diseases.
Bacterial Structure
Not all bacteria have all the
features shown.
• Bacteria belong to a large
group of organisms called
prokaryotes which lack a
nucleus.
• All organisms that have a well
defined membrane - bound
nucleus are called eukaryotes
e.g. animals, plants, fungi and
some single-celled organisms.
Capsule
70S
Ribosome
Mesosome
Plasmid
Cell Wall
Cell Membrane
Nucleoid
DNA
Flagellum
1mm
Cell wall
peptidoglycan
• Rigid cell wall provides protection and
maintains shape.
• Made from peptidoglycan (modified
sugars with polypeptide cross links);
in addition some bacteria may have
lipids, proteins and
lipopolysaccharides in their cell wall.
• Surface projections (pili) made from
cylinders of the protein pilin allow
bacteria to link to each other, to other
cells and to substrate.
Peptide bridge/cross link
Capsule
• Outside the cell wall of some
bacteria is a slimy layer of
polysaccharides or
polypeptides called a
capsule.
• Protects cells against
phagocytosis, desiccation,
antibiotics, enzymes, etc. and
allows them to attach to other
cells.
Capsule
70S
Ribosome
Cell Wall
Cell Membrane
Mesosome
Nucleoid
DNA
Plasmid
Flagellum
1mm
Flagella
•
•
•
Some bacteria have a flagellum,
enabling movement.
They can be arranged differently
on different bacteria; single
flagellum or groups of flagella at
one end or flagella arranged
around the cell. The type of
flagellation is used to help identify
bacteria.
Bacterial flagella have a
complicated structure of fibres
made from a contractile helical
protein called flagellin rotating the
flagellum like a propeller.
Flagella
Plasma membrane
• Consists of a thick lipid and
protein layer.
• Controls the movement of
small molecules in and out of
the cell.
• Folding of the membrane into
mesosomes increases surface
area for metabolic activity,
including aerobic respiration.
Capsule
70S
Ribosome
Cell Wall
Cell Membrane
Mesosome
Nucleoid
DNA
Plasmid
Flagellum
1mm
Genetic material
•
•
•
•
•
The genetic material is contained in a tight
folded mass of circular DNA and RNA called
a nucleoid.
The DNA is normally a single circular strand
of about 4000 genes with information for cell
metabolism, growth and reproduction.
70S (smaller) ribosomes and plasmids can
also be seen under the EM.
Ribosomes are sites of protein synthesis
and plasmids are circular pieces of DNA
found in addition to the DNA in the nucleoid.
Plasmids contain varying numbers of genes
not essential to the survival of the cell, but
may contain genes for antibiotic resistance
that can be passed from one bacterium to
another.
Comparing prokaryotic and eukaryotic cells
Feature
Prokaryotic Cell
Eukaryotic Cell
0.1 -10 μm (smaller)
10 -100 μm (bigger)
Nucleus
No
Yes
Chloroplasts
No
Yes (plants)
Mitochondria
No
Yes
Endoplasmic reticulum
No
Rough and Smooth
Golgi apparatus
No
Yes
As circular DNA free in
cytoplasm
Enclosed in the nucleus
Small 70S
Large 80S
Cell Wall
Peptidoglycan
Cellulose (plants), chitin
(fungi)
Aerobic respiration
In mesosome
In mitochondria
Size (μm)
DNA
Ribosomes
Vibrio cholerae
•
Vibrio cholerae is a food - and waterborne bacterium prevalent in areas of
poor sanitation where water or food is
faecally contaminated.
•
Naturally occurs in plankton and is the
species of bacteria that causes cholera.
•
Highly motile with a single flagellum and
appears to shake (Vibrio comes from the
Latin to vibrate).
•
Like many other pathogens it contains
plasmids that contain genes for antibiotic
resistance that it can transfer to other
Vibrio cholerae cells.
Vibrio cholerae
Question
Which of the following are structural features of Vibrio cholerae?
?
A cell membrane
?
A single flagellum
?
A cell wall
?
Rough endoplasmic reticulum
?
A plasmid