Page 165 - The Miracle of Hormones

The Zip Code System Within Cells

How is Protein Traffic Within Cells Organized?

Everyone knows that a zip
code system is designed to in-
crease the efficiency of communi-
cation by getting a letter to the
correct address as quickly as pos-
sible and with the fewest errors.
The really interesting thing is that
research has shown that a similar
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mechanism exists within cells. It
is known that proteins are synthe-
In order for a letter to reach the right address,
sized by the planned union of it must have a clear address and zip code writ-
hundreds of amino acids. A spe- ten on it. In a similar way, every newly pro-
duced protein has a special zip code chain
cial section of between 10 and 30
that shows it where it will go.
amino acids form a kind of chain
that forms the zip code of the protein. In other words, the zip code written
on the envelope is composed of numbers and letters, while the zip code in
a protein is composed of amino acids. This code is located on one of the
ends of the protein or inside it. As a result, every new protein that is syn-
thesized receives instructions as to where it will go inside the cell and how
it will go there. Now, let us examine under a highly advanced microscope
the journey of a protein within a cell.

Smooth Secretion
endoplasmic Golgi complex
reticulum Some elements in a cell are illustrat-
Plasma membrane
ed in this diagram that shows how
Mitochondrion Signal chain proteins are directed by the cell's zip
code system. (Chloroplast is an ele-
Proteins ment found only in plant cells.) On
Signal chain
Nucleus every newly synthesized protein
Proteins Signal chain there is built in a special zip code
area formed by a chain of amino
acids. This chain normally occurs on
Chloroplast the end of a protein and guides the
protein to its target within the cell.

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