Cholera

Learning Objectives What are prokaryotic cells? How do prokaryotes differ from eukaryotes? What causes cholera and how does it produce the symptoms? How ORS works with reference to biological principles.

Cholera & ORS Revision Learning Objectives: Focus revision by identifying core concepts to revise as well as the principles that explain the mode of action of the cholera toxin. Explain how the pathogen causes the diseases and how

How do people get infected with vibrio cholerae ? Drinking contaminated water and less commonly food contaminated by the bacteria

Vibrio cholerae bacteria A curved rod shaped bacterium with a flagellum. Bacteria are examples of prokaryotic cells.

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.

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 the Cholera bacterium causes disease (1) The bacterium is transmitted by the ingestion of water and rarely food contaminated with faeces containing the pathogen. Upon reaching the stomach, almost all the bacteria are killed by the acids in the stomach. When surviving bacteria reach the intestine they use their flagellum to propel them through the mucus lining of the intestinal wall. They start to produce a protein toxin. It has two parts. One part binds to specific carbohydrate receptors on the cell surface membrane. These receptors are only found on the epithelial cells of the small intestine, this explains why cholera toxin affects this region of the body.

Lumen of the small intestine CL- Toxin CL- CL- Chloride Channel Water CL- Chloride Ion CL- CL- CL- CL- CL-

Absorption in the small intestine

Exam question S(d) The cholera toxin affects the movement of ions through the intestinal wall. It causes the loss of chloride ions from the blood into the lumen of the small intestine. This prevents the movement of sodium ions from the lumen of the small intestine into the blood. (i) Describe how sodium ions normally enter the blood from the cells of the intestinal wall against a concentration gradient. ....................................................................................................................................................

How does the bacterium cause diarrhoea? Lumen of small intestine Toxin Cl- Cl- Chloride Channel Cl- Cl- Water

Where does the toxin target?

Identify the different parts and functions of a typical bacteria

They have a few feature in common, but what are the main differences?

Distinct nucleus, with a nuclear envelope 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 Where present cell wall is made mostly of cellulose (or chitin in fungi) Cell Wall made of peptidoglycan

Distinct nucleus, with a nuclear envelope 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 Nucleolus present Circular strands of DNA but no chromosomes Chromosomes present, in which DNA is located 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 smaller (70S type) Ribosomes are larger (80S type) ER , Golgi apparatus and lysosomes present No ER, Golgi apparatus and lysosomes Where present cell wall is made mostly of cellulose (or chitin in fungi) Cell Wall made of peptidoglycan

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.

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.

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