Lec 3.docx

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University of California - Irvine
Biological Sciences
Peter A.Bowler

e109 Monday oct 3 -there is nothing pushing molecules down a concentration gradient---they are moving randomnly -Eventually, the concentration would have been about the same inside and outside the cell of O2 and CO2; Concentrations would be homogeneous, delta C would be zero, no (0) net diffusion (although cards still moving) Rate of diffusion described by Finnick’s law -one chemical entity at a time when talking about diffusion -diffusion can be considered between two planes, across one plane horizontally not vertically, or between two points -Rate of diffusion is directly proportional to a) surface area: measured perpendicularly to rate of diffusion (so vertically) b) 1/thickness or 1/distance or inverserly proportional to thickness diffusion d c) concentration difference (change =C2-C1) d) concentration gradient which is concentration difference/distance)---delta C/distance; not the same as concentration difference; huge concentration differences across a distance Diffusion across membrane -Membrane must be permeable to particular chemical species -membranes are lipid bilayers with many inserted proteins -inside of cell is chemically distinct from outside of the cell -areas of higher concentration to lower concentration -O2 and CO2 and water can readily move across the membrane -large molecules and charged molecules (ions) cannot pass through the lipid bilayer Channels and carriers are membrane proteins involved in transport -the ECF must be interstitiual fluid because no blood cells -channels create an opening or pore through which a chemical species can move; do not have to always be open -carriers reconfigure due to a ligand to carry a molecule to the other side -gated channels are usually closed. They open in response to chemical, mechanical or electrical signals -channels, carrier proteins, and gated channels are examples of facilitated diffusion?? Different kinds of carriers -Uniport carriers: only carry one type of substrate +GLUT transporter makes the membrane permeable to glucose if there is a concentration gradient; facilitat
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