Page 122 - The Miracle of Protein

120 THE MIRACLE OF PROTEIN

grabs the protein and carries it to the endoplasmic reticulum.
As a result, protein is either inserted into the membrane or tak-
en inside the organelle. For these processes to take place, re-
quires a receptor complex, one protein to enable passage
through the membrane and another for its insertion. After
these stages are completed, the SRP molecule returns to cyto-

plasm and begins carrying new proteins.

Passing the Protein Through the
Membranes

Compared to most all proteins, the cell is a very large
structure and incorporates a myriad of special regions called

organelles. Organelles are surrounded by lipid bilayers. We can
compare these lipid bilayers to the exterior sidings of buildings
that are so sturdy that some won’t allow the passage of a single
hydrogen ion. The fact that proteins, which are like skyscrapers
in the world of molecules, can pass under these stringent cir-
cumstances is a marvel of engineering. To enable this, special
proteins called translocators are created in the membranes.

These translocators are charged with passing proteins through
the membranes, and they had to have existed since the first mo-
ment of life, because without them, the cell would immediately
die due to the lack of proteins that couldn't be taken to their
places of duty.
For instance, there are special gates on the nuclear mem-

brane called ‘pores’ consisting of 3000-4000 proteins of 50 dif-
ferent types that are used to construct the pores. The diameter
of one pore in the nucleus is 9 nanometers, in other words, if
100 million were bound together, they would be only 1 m
48
long. At this point, scientists have discovered a marvelous