Vibrio Cholera

Vibrio Cholera:

Rod/comma shaped bacterium, which can cause dehydration through diarrhoea, 

It can be ingested through 

• Contaminated water
• Food, or preparation

It affects the body through a toxin that it produces, the toxin only affects the upper region of the small intestine as this is the only region with membrane receipts that complement the toxin. 

How:

Many of the organisms are destroyed by the stomach acid, but in the case of a less acidic stomach some bacterium may survive into the small intestine, using their flagella in a corkscrew motion they will pass the mucus layer and anchor itself into the duodenum.

The bacteria will then produce an exotoxin, that binds to specific receipts of the cell surface membrane, and activates the chloride ion channel in the cell membrane. 

This causes the chloride ions to diffuse out of the cells into the lumen. 

Therefore the water potential in the lumen is lowered, so the water moves by osmosis, down its water potential, out of the cells and into the lumen. Producing diarrhoea and dehydration.

Treatment: 

Oral rehydration therapy (ORT), replaces lost water and salts, 

Drink a solution of sugar and salt and water, 

Which will be taken into the cell by the co transported protein, lowering the water potential in the cell, increasing the gradient between the cell and the gut. Therefore water is then taken up by osmosis, back into the cell. Rehydratic cells and reducing diarrhoea. 

Prokaryotes and Eukaryotes

Differences between Prokaryotic and Eukaryotic cells: 

Endotoxins are produced from the break down of bacteria (cell walls) and are lipopolysaccharides, 

Exotoxins are proteins, which are secreted from living cells. 

Prokaryote cells

• Cell membrane: regulates entry/exit, as it is selectively permeable, 
• Mesosome: respiration and cell division 
• Cell wall: Protection, prevents osmotic lysysis, (water moving into the cell), made of peptidoglycan. 
• Slime layer/capsule: Protection e.g. against antibiotics,
• Flagellum: Movement of cell, 
• DNA: circular, free in cell, containing genetic material. 

Eukaryotic Cells

Magnification

  

• Resolution: The ability to distinguish between two separate points, Electron microscopes have a higher resolution than light microscopes as they use electrons, as they use electrons (which has a shorter resolution than light). Shorter resolutions allow for better resolution than longer wavelength. Some times microscopes have blue filters to allow for this as blue has the shortest wavelength. 
• Magnification: Indicates how much bigger the image is than the original object. Simply given as a magnification factor e.g. x100, By using more lenses microscopes can magnify by a larger amount, but the image may get more blurred, so doesn't mean that more detail can be seen.
• Light Microscopes: Oldest, simplest, and most widely used microscopes. Specimens illuminated with light, which is focused using glass lenses and viewed using the eye or photographic film. Specimens can be alive or dead, but often need to be stained with colour to make them visible. 
• Electron Microscopes: This uses a beam of electrons, rather than electromagnetic radiation, to “illuminate” the specimen. Electrons behave like waves and can be easily produced (using a hot wire), focused (using electromagnets) and detected (Phosphor screen or photographic film). A beam of electrons has a very useful wavelength of less than 1nm, so can be used to view sub cellular specimens. 
• Transmission Electron microscopes (TEM): work like light microscopes, transmitting a beam of electrons through a thin specimen and then focussing the electrons to form an image on the screen or on a film. This is the most common form of electron microscopes and has the best resolution (<1nm)
• Scanning Electron microscopes (SEM): scan a fine beam of electrons onto a specimen and collect the electrons scattered by the surface, this gives poorer resolution, but means you can view the final image in 3D.

Cell Fractionation

The process of separating different parts and organelles of a cell, so that it can be studied in greater detail. The most common method is differential centrifugation. 

This is where the organelles are separated due to their different densities. 

There are three key stages: 

1. Homogenisation 
2. FIltration 
3. Centrifugation 

Homogenisation: 

Pestle and mortar or a blender to break open the cells. You will need and ice cold, isotonic buffer solution:  

• COLD: This reduced enzyme activity and will reduce autolysis (self destruction) of the organelle. 
• ISOTONIC: To prevent osmotic movement where swelling of organelle may cause lysis or shrinkage of the organelle, both processes will result in the destruction of its natural function. 
• BUFFER SOLUTION: Preventing any change of pH, which may damage the organelles, either by denaturing the enzymes or the proteins affecting its function. 

Filtration: 

This is to remove any debris (unbroken cells, cartilage etc). This will prevent contamination of the pellets resulting from the centrifugation. 

Centrifugation: 

Homogenate is centrifuge at different speeds, The speed and length of centrifugation will increase each time. The densest organelle sinks to the bottom, and the remaining solution, the supernatant, is separated for further centrifugation. 

Naughty Monkeys Like Eating Raspberries 

• Nuclei 
• Mitochondria 
• Lysosomes 
• ER 
• Ribosomes

Cells and Water

Since cells contain various Biological Molecules, such as Sugars and Salts, they have a Water Potential lower then 0 kPa. Water may move in or out of a cell depending of the Water Potential Gradient between the inside of the cell and its  environment.

 When water diffuses into a plant cell, when it is placed in a solution of higher Water Potential than inside it, the cell contents will expand. However, since plant cells are surrounded by a strong cell wall, they will not burst. The cell contents will push against the cell wall, and the cell will become Turgid.

If a plant cell is placed in a solution of lower Water Potential, water will diffuse out. This causes the Cytoplasm to shrink and become Flaccid. If enough water leaves, the Cytoplasm will pull away from the cell wall. The cell will become Plasmolysed.  

 Animal cells will also expand when they are placed in a solution of higher Water Potential. Since animal cells do not have cell walls, if this happens excessively the cell will burst open and become Haemolysed.

If water leaves an animal cell by Osmosis, it will shrink and appear 'wrinkled'. It will become Crenated.