Page 166 - The Miracle of Hormones

THE MIRACLE OF HORMONES

When we look at how a newly synthesized protein, goes to its prop-
er place—for example, endoplasmic reticulum—we see the following:
First, the zip code is read by a particle of a molecule called SRP. SRP
(Signal Recognition Particle) is a structure especially designed to read the
zip code and to help the protein find the channels through which it must
pass. It interprets the code in the protein, binds to it and shows it the way
like a real guide. Then, the SRP and the protein lock into a protein pas-
sage channel and a receptor on the membrane of the endoplasmic reticu-
lum specially designed for them. When the receptor is stimulated in this
way, the channel on the membrane is opened. At this stage, the SRP sep-
arates from the receptor. All these operations occur with perfect timing
and harmony.
At this point, the protein encounters a problem. It is known that pro-
teins are formed when the amino acid chain bends and contorts into a

Proteins produced inside a cell are in constant motion, as illustrated in this
picture. In the bottom left corner, note the SRP molecule that guides pro-
teins to the places they are to go.

Membrane protein
Plasma
Secreted protein membrane

Vesicle

Messenger RNA

Ribosome Translocator
protein
Signal peptide
Golgi apparatus Lumen
Signal peptide
Lumen
Mitochondrion
protein
SRP
Endoplasmic
reticulum

Nuclear pore
complex
Ribosome receptor
Signal peptide Nucleus protein
SRP receptor
Lumen