The Journey of a Message-Carrying
Hormone Inside the Cell
When a messenger molecule reaches a cell, it attaches
to an antenna on the cell's membrane. While it
is attached, it relays its message to the antenna.
The message passes to the tail of the antenna
that is inside the cell. After this, the antennae
parts that were previously single come together
in groups of two. The enzymes in the body section
pair up and add phosphates on each other's tails,
thereby changing the shape of the tail section.
These operations are like a call to the messenger
modules inside the cell.
When a messenger molecule reaches the cell, it attaches
to the antenna on the cell's membrane. In the course of
this attachment, the message is relayed to the antenna.
The message received by the antenna is then transmitted
to the tail located in the inner section of the cell.
The body of the microscopic communications antenna enters
the fluid (cytoplasm) between the nucleus of the cell
and its membrane. The connection established between the
hormone and the antenna initiates a chemical reaction.
This reaction causes the antennae, which were individual
units, to form into groups of two, and brings about a
change in the shape of the tail sections. This operation,
called "phosphorilation," is a change that occurs when
the enzymes in the body section add phosphate to the tail.
A computer simulation showing the union between
a growth hormone and a receptor.
Several molecules and proteins add technical support to
this system. For example, the GTP molecule and the proteins
called "G" for short, have an important effect at this
stage; they supply the phosphorous for the phosphorilation.
For the system to function, it is necessary that many
factors come into play at the right moment.
A base station
This operation carried out by the enzymes has an important
role in the relay of information. This operation within
the cell is intended to be a call to the proteins known
to be communication modules in the cytoplasm. As a result
of a number of complex operations, the SH2 communication
module is activated, and a connection is established
with the tyrosine kinase antenna, which stimulates the
relay of this message within the cell.
Until recently, no one had any idea of how the messages
carried by hormones reached the nucleus so speedily
and with such precision. How is it that no error is
made in the course of the transmission of the message?
Indeed, the slightest error made in the process of the
transmission of a message would cause, for example,
a faulty protein production in the cells and the collapse
of a marvelous physical system. The latest research
has shown the existence of communication modules in
cells. The SH2 module is only one of an estimated hundreds
of different communication modules.
Within the cells, these modules function as communication
stations. Thanks to the wonderful system that they have
established, messages are carried from the membrane
of the cell to its nucleus. From one point of view,
these fantastic modules can be compared to base stations
that establish communication with cell telephones. In
this way, enzymes that work in an ordered fashion deep
in the nucleus of a cell take measures to ensure that
production occurs according to "ideal standards."
|Because of the marvelous
system created by the modules, the message is sent
from the cell membrane to the nucleus. These wonderful
modules can be compared to base stations that make
communication possible between cell phones.
Modular Communication Stations
In this picture you can see the passage channels
on the membrane of a cell. These channels are
made of protein and carefully supervise entrance
and exit in and out of the cell.
Research done on these communication stations has surprised
scientists. The structure of the modules is composed
of proteins, each made up of 100 amino acids. Each one
of these has a particular three-dimensional structure.
As a result of this marvelous design, every protein
can establish a connection with a certain module. That
is, just as every radio station broadcasts on a different
frequency, different messages are relayed by different
cell communication modules.
The idea of a "module" used here to describe the bits
of protein that form the communication pathways in the
cells is really an insufficient comparison. This analogy
explains that these three-dimensional molecules fit
into each other as do separately manufactured parts
of a pre-fabricated house. What amazes scientists is
the structure that emerges as a result of adding phosphate
onto the receptors is a shape with which the SH2 module
can bond completely. Thanks to this, the SH2 module
and the receptor can fit into one another as if they
were designed for that very purpose.
With the help of an electron microscope
capable of enlarging an object one million times, some
stages have been observed which enable us to understand
the microscopic communication stations, but scientists
inform that there are still hundreds of communication
modules whose structures are not yet understood.45
These cohere closely with one another and form an inerrable
system of signals within the cell. If one of these modules
were not in place, or if it were faulty, communication
within the cell would be completely paralyzed; this
shows how extraordinary this system is.
The reason why we use the term "module"
to describe the protein particles that make up
the communication pathways in cells is to explain
that these three-dimensional molecules fit into
one another like the separately manufactured pieces
of a pre-fabricated house.
This marvelous communication system in the cells has
a few "expert modules" that take the message they have
received from receptor on the membrane directly to the
relevant gene in the cell's nucleus. That is, these
modules have such a flawless design that they find the
section of that information contained in the DNA molecule
relevant to the message they are carrying (enough information
in a human to fill a million encyclopedia pages). In
this way, they ensure that the amount of protein required
by the cell is produced without error. That a piece
of protein one millionth of a millimeter in size can
be so clever and aware is a wonder.
All of these investigations show that the cytoplasm
of the cell is full of various organelles and proteins,
and, once again, that the cell is the most complex structure
in the universe. The internal communication system of
the cell is an example of this. Certainly, the splendid
order in the world of cells is the order of God, the
Lord of all the worlds.
computer simulation of the SH3 module
computer simulation of the SH2 module.
45 J.Schultz, R.R.Copley, T.Doerks, C.P.Ponting,
P. Bork, "SMART: a web-based tool for the study
of genetically mobile domains," Nucleic Acids Research,
Vol.28, No.1, 2000, pp. 231-234