Microbial Physiology notes lec15 10-29-10

Microbial Physiology notes lec15 10-29-10 - Microbial...

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Microbial Physio Lecture 15: Sensing Physical Forces by E.coli continued October 29, 2010 1. Humans: can also respond to magnetic fields a. Some humans have immutable sense of direction i. The variation of magnetosomes can vary up to 100 fold in the brain of different people ii. The presence of magnetosomes and [ ] of them are genetically determined b. Human tissue culture cells respond to imposed magnetic fields c. Imposition of strong magnetic field ( 100x that of the earth) to the brain of epilepsy patients a10x increase in the frequency of seizures i. Illustrates that humans are in fact subject to alterations in magnetic forces d. Continual exposure to power lines has been reported to incidence of cancer in people e. Crystals of magnetite (Fe 3 O 4 ) have been identified in human brains and brain tissues of many animals ( by magnetic resonance imaging (MRI)) i. They measured the crystalline structure of the magnetosomes ii. The crystals are always about the same size (42-45 nm in diameter) and same shape (cubo-octahedral—have 8 sides and kind of look like cubes) regardless of the organism, but are present in the brain in 100x lower [ ] than in bees brains f. In animals, the presence of magnetosome is coupled to neurons and therefore can generate nerve impulses but this takes many nerves to be activated i. Magnetosome movement opens up ion channels to generate nerve impulses 2. bacteria have magnetosomes consisting of: a. bacteria also have magnetosomes, but 1 isn’t going to do much, there needs to be many to allow the bacteria to orient w/in the magnetic field that it finds itself in i. many bacteria don’t have magnetotaxis ii. what determines whether or not the bacteria has magnetosomes in their brain? 1. If bacteria are in the south/north pole, then it is in a position to respond to magnetic fields and orient in response to the field 2. magnetotaxis is sometimes a misnomer because the bacteria use it for orientation, but they don’t necessarily swim up/down a. what usually happens is the bacteria couples magnetotaxis—which is orientation in a magnetic field—the bacteria is so small that it cant sense gravity, so at the poles it cant sense gravity ( no
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bacteria can sense gravity) so instead to tell the bacteria which way is up/down, the bacteria responds to the magnetic field, and then usually it responds to some nutrient like: oxygen, presence of nutrient at the bottom of the lakes b. Fe 3 O 4 (magnetite) or Fe 3 S 4 (greigite) (also other sulfides: pyrites) crystals are surrounded by a membrane of unique lipids and proteins. i. The valance of oxygen/sulfur is -2, it is always -2 ii. Valance of iron can be either 2+/3+ iii. Fe 3 O 4 (magnetite) the valance of the 4 oxygens= -8; the total valance of iron=+8 1. but not divide the +8 by 3 irons and get 2 (+3) and 1(+2) and this is the characteristic of iron oxide, and its all Fe +3 / Fe +2 it isn’t going to be magnetic, it has to have the right combination of iron to oxygen/iron to sulfur
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Microbial Physiology notes lec15 10-29-10 - Microbial...

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