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Cholera as a prokaryote This demo only contains a sample of the full content 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