07cells1-1 - Lecture 7 Cells 1: The endomembrane system Why...

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Lecture 7 Cells 1: The endomembrane system
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Why cells are small Prokaryotes/Eukaryotes The Endomembrane System
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Why are cells small?? Because most chemical reactions in cells require diffusion: Diffusing molecules don’t travel long distances because of their “random walk” Distance traveled is proportional to square root of time: Big molecule travels 10µm in 1s (distance=10 x 1) In 1 min: 10 x 60=77µm In 1 h: 10 x 3600=600µm
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Why Cells are Small 10 6 sides x 10 2 = 600 mm 2 1/1.7 10 3 = 1000 mm 3
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Cell size is limited by the need for a high surface area-to-volume ratio. Only a high surface area compared to the volume allows diffusion to take place fast enough . Increasing size (= volume) of a cell decreases the surface area-to-volume ratio dramatically, because volume increases with the power of three, but surface area only with the power of two .
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The Scale of Life
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Cells show two organizational patterns: Prokaryotes are very small. They have no nucleus and hardly any membrane-enclosed compartments. Eukaryotes have a membrane-enclosed nucleus and many other membrane-enclosed compartments called organelles, and can therefore be larger than prokaryotes.
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Prokaryotes inhabit the widest range of environmental extremes, because they show the
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07cells1-1 - Lecture 7 Cells 1: The endomembrane system Why...

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