Microbial Physiology notes lec23 11-19-10

Microbial Physiology notes lec23 11-19-10 - Microbial...

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Microbial Physio Lecture 23: Circadian Rhythm in Synechococcus elongatus November 19, 2010 (guest lecture) 1. Earth’s rotation is a constant a. The sun moves across the sky and the plants track the sun across the sky as the planet rotates, and then night comes and the leaves go limp because there is no sun to excite their photochrome, but then just before dawn, all of the leaves point east, before there is even any sun in anticipation of the sun rising b. So its not so much that the plants are tracking the sun, but its more that the plants are tracking the sun’s movement 2. What organisms have circadian rhythms? a. Plants, mammals (mice people), birds, fungus, Synechococcus elongatus(bacteria) b. The question is, why would an organism such as Synechococcus elongatus that has a dividing time that is less than 24 hours? 3. Working definition of Circadian rhythm systems a. They have to occur over a ~24hr cycle most organisms that have circadian rhythms if you don’t give them any external cues, then it will develop longer/shorter than 24hr circadian cycles b. Entrainment of circadian rhythms happens by external signal i. Light and dark pulses ii. Warmer and colder (changes in temperature) 1. The light and dark, and the warm and cold are the major things that happens when the sun rises and sets sun rises it gets lighter and warmer, and when the sun sets, it gets darker and colder these sorts of things helps reset organisms circadian clocks and it depends on the organisms for which signal it responds to 2. Some organisms can respond to both c. Circadian rhythm can be maintained in the absence of an external signal
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i. Ex. If we were to close all of the blinds in the room and were to stay in the room and leave the lights on and never turn them off, we would all start to feel sleepy about the time that we go to bed, and would wake up at about the time that we’re supposed to wake up, we would even feel hungry or have to go to the bathroom at around the same times that we have to do those things a lot of these fxns are controlled by our circadian clocks, and once the circadian clock is set, it continues to run, even in the absence of external signals 1. If the lights are on, and we’re in the room for 24 hrs, we are going to keep our circadian rhythms going, but if we suddenly shut the lights off, but keep the lights off for 12 hrs and then turn them back on, most of us will respond to it as its near dawn, so the absence of external signal is keeping the lights 2. entrainment means that you change the conditions in some way to reset the clock, and that causes the organism to think that it’s a specific time of day a. if we shut the lights off for 12 hours and then turn it back on, most of us will reset out clocks and be thinking that its dawn d. Circadian systems have to be temperature compensated i. The circadian rhythm has to be able to respond to temperature, but the clock itself needs to be stable over range of temperatures
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Microbial Physiology notes lec23 11-19-10 - Microbial...

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