Page 134 - The Miracle in the Cell Membrane

roteins do not float free ly in the cell; their
move ments with in the cell are tight ly con -
trolled. Inside the cell, there are com part -
ments just like rooms in a house. The walls
of the com part ments with in the cell are equipped with a
gate and chem i cal recep tors. If a pro tein with the cor rect
iden ti fi ca tion tag approach es, the recep tor gate opens and
lets the pro tein pass through. If a pro tein with the wrong
tag approach es, the gate remains closed. In order for this
pas sage to take place, the gate, recep tor and tag all need to
be present at once. The organ where these proc ess es can be
observed most clear ly is the liver, the larg est organ in the
body and which con trols the lev els of essen tial nutri ents,
such as pro teins, in the blood. If the gate, recep tor and tag
were not present at the same time in the liv er's cell mem -
branes, then the liver itself and con se quent ly, the body
would be una ble to sur vive. Moreover, this is only one of
the pre con di tions for life.
In the pre vi ous chap ters, you read how some of the pro -
teins in the cell mem brane serve as chan nels. The pas sage
of sub stan ces through them varies accord ing to the diam e -
ter of the chan nel, its shape and inter nal elec tri cal charge.
As the result of exper i ments he car ried out with the sup -
port of the US National Academy of Sciences, the bio chem -

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