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Cholera
Learning Objectives
• What are prokaryotic cells?
• How do prokaryotes differ from eukaryotes?
• What causes cholera and how does it produce
the symptoms?
Where does the toxin target?
What does it do?
• The primary symptoms of cholera are profuse painless
diarrhea and vomiting of clear fluid, which leads to
dehydration.
• An untreated person with cholera may produce 10–20
litres of diarrhea a day with fatal results.
• For every symptomatic person there are 3 to 100 people
who get the infection but remain asymptomatic.
What is responsible?
• Vibrio cholerae
– A curved rod shaped bacterium with a flaggelum.
– Bacteria are examples of prokaryotic cells.
A Typical bacteria (an example of a
prokaryotic cell)
Cell Wall
• Made of peptidoglycan
• Physical barrier that protects against
mechanical damage and excludes certain
substances
Capsule
• Extra protective layer which can also helps
groups of bacteria stick together
Cell Surface membrane
• Differentially permeable layer
• Controls entry and exit of chemicals
Flagellum
• Aids movement of bacterium due its rigid,
corkscrew shape and rotating base help the
cell spin through fluids.
Ribosomes
• 70S type (smaller than the 80S type in
Eukaryotic cells)
• Protein synthesis occurs at ribosomes; it can
be inhibited by certain antibiotics. The
difference between prokaryotic (70s) and
eukaryotic (80s) ribosomes allows antibiotics
to selectively target the prokaryotic ribosomes
while sparing eukaryotic ribosomes.
Circular DNA and Plasmids
• Circular DNA possesses the genetic information for
the replication of bacterial cells.
• Plasmids can reproduce independently meaning
they have use as vectors in genetic engineering. They
possess genes that that aid the survival of bacteria
by producing enzymes that can break down
antibodies.
They have a few feature in common,
but what are the main differences?
Some of these are mixed up. Can you put them in right place?
Prokaryotic Cells
Eukaryotic Cells
No true nucleus, only a diffuse area of
nuclear material with no nuclear envelope Distinct nucleus, with a nuclear envelope
Nucleolus present
No nucleolus
Chromosomes present, in which DNA is
located
Circular strands of DNA but no
chromosomes
Membrane bounded organelles are
present
No membrane bounded organelles
No chloroplasts, only photosynthetic
regions in some bacteria
Chloroplasts presents in plants and algae
Ribosomes are larger (80S type)
Ribosomes are smaller (70S type)
ER , Golgi apparatus and lysosomes
present
No ER, Golgi apparatus and lysosomes
Cell Wall made of peptidoglycan
Where present cell wall is made mostly of
cellulose (or chitin in fungi)
Did you get it right?
Prokaryotic Cells
Eukaryotic Cells
No true nucleus, only a diffuse area of
nuclear material with no nuclear envelope Distinct nucleus, with a nuclear envelope
No nucleolus
Circular strands of DNA but no
chromosomes
Nucleolus present
Chromosomes present, in which DNA is
located
No membrane bounded organelles
Membrane bounded organelles are
present
No chloroplasts, only photosynthetic
regions in some bacteria
Chloroplasts presents in plants and algae
Ribosomes are smaller (70S type)
Ribosomes are larger (80S type)
No ER, Golgi apparatus and lysosomes
Cell Wall made of peptidoglycan
ER , Golgi apparatus and lysosomes
present
Where present cell wall is made mostly of
cellulose (or chitin in fungi)
How do people get infected with vibrio
cholerae ?
How do people get infected with vibrio
cholerae ?
• Cholera is transmitted by the ingestion of
water, or food that has been contaminated
with faecal material containing the pathogen.
• Can you think of ways that this contamination
might happen?
• How about ways to prevent it from
happening?
How does the bacterium cause
diarrhoea?
• Most are killed in the stomach. Some survive and propel
themselves using their flagellum through the mucus lining of the
small intestine wall.
• They then produce a toxic protein. One part binds to specific
carbohydrate receptors on the cell surface membrane of intestinal
epithelial cells. The second part enters the epithelial cells, causing
chloride channels to open.
• Chloride ions leave the cell and enter the lumen of the small
intestine. This raises the water potential of the epithelial cell and
lowers the wp of the lumen. Water flows from the cells to the
lumen by osmosis.
• Ions leaving the epithelial cell creates a concentration gradient and
ions from the blood diffuse in to replace them. Water follows by
osmosis.
How does the bacterium cause
diarrhoea?
Lumen of small
intestine
Toxin
-
Cl
Chloride
Channel
Water
-
Cl
-
Cl
-
Cl
Questions
• 1. Which organ does the cholera toxin target?
Why is its action so specific?
• 2. How does the cholera toxin cause
diarrhoea?
• 3. Suggest three measures that may be used
to limit the spread of cholera.
• 4. Suggest how inhibiting flagellum
development in the pathogen may prevent
the disease.
• Extension: Q2,Q4 on page 67 of textbook