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A cell is at very least
a wall that separates inside from outside.
Of course, as the cell developed
in water, the stuff that was being separated into "inside"
and "outside" had to be water and some things dissolved
in water.
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How many types of building
blocks does it take to make a wall? At least one, a special fat
(lipid) with a polar end and two tails.
The polar head is attracted to
charged water. the other end, with the twoi tails, gets pushed
away from water, making a ball or finding the water's surface.
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(Alberts Access Excellence)
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Two rows of these lipids
make up much of our cell walls. One half of them face in and
half face out. Why? What is the advantage?
They make a SPACE in between them
that can keep things out.
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(Alberts Access Excellence)
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(Alberts Access Excellence)
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All sorts of proteins are stuck
in the cell wall. They help hold it together and do different
jobs.
There are big arguments about which
came first, the fats in the wall or the proteins stuck in the
walls.
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(Alberts Access Excellence)
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Every one
of these protein types is interesting, but we are going to concentrate
on the ones called "transporters" right now. In order to get big material in and out
of a cell wall, there needs to be holes. (The small stuff can
diffuse right through the lipid membrane.)
There are holes
all over the outside of a cell surface. Experiment with this
animation and make see what size particles can get through when
you change the holes. (SEE FLASH ANIMATION)
In real cells,
some holes are large enough to let lots of sized materials get
through. But many are made to just let in particular sized molecules
get through.
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(Alberts Access Excellence)
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Here is a LARGE picture of ions
(blue) trying to get through the protein pore (red alpha helixes).
You can see them getting into a protein
pore. (Sanson pix 1)
A cell can also
use FORCES and SHAPES to move the molecules through the membrane.
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NOW, ADD SOME
SUGAR ON THE TOP OF THE MEMBRANE
On the top of the
membrane, branching sugars are attached both to lipids and to
proteins sticking through of the membrane. The sugar provides
identifiers for the cell, a way for the cell to talk to other
cells. It also makes the cells slippery, so they don't get stuck
to one another.
Here is the membrane
assembled: 
See http://www.cchem.berkeley.edu/%7Ecrbgrp/
Berkeley
RESOURCES
http://www.accessexcellence.org/AB/GG/
index to Alberts graphics on the web in Access Excellence
http://www.accessexcellence.org/AB/GG/memPerm.html
!getting through lipids - models Alberts
!!http://www.accessexcellence.org/AB/GG/passActiveTrans.html
passive and active transport
http://gwis2.circ.gwu.edu/~atkins/Neuroweb/plasmalemma.html#cell
!!!!This page has many of the components. If we could translate
this, it would be super.
http://www.accessexcellence.org/AB/GG/pMembranes.html
plasma membrane proteins
http://www.accessexcellence.org/AB/GG/macroMols.html
Macromolecules in cells - percentages
http://www.accessexcellence.org/AB/GG/aminoAcids2.html
the Amino Acids (from Alberts)
http://www.accessexcellence.org/AB/GG/sugarTypes2.html
Sugar types, from Alberts
These can be printed from PDF file
http://www.accessexcellence.org/AB/GG/protein.html
4 levels of protein structure
http://www.accessexcellence.org/AB/GG/collagen_Elastin.html
Collagen and elastin Alberts