What are Proteins?
Proteins are what makes you, you! They are the workers in you
cells that carry out specific jobs. Proteins are found in plants,
bacteria, viruses, and humans. In our bodies, we have trillions of
cells. In each of those cells, there are many protein workers that
have a specific job to do. In order to
complete these jobs, proteins must
work together and help each other
out. In this module, you will learn
how protein pathways work and then
analyze a specific protein found in
fruit flies and humans.
To the right is an example of a
common protein called keratin. This
protein is found in your hair and skin
and helps make it strong. Here is
what keratin looks like:
What are the different
types of proteins?
Enzymes
Enzymes are catalysts that speed
up the breaking apart and putting
together of molecules. Enzymes
are usually studied in a class of
their own, but it is important to
remember that enzymes are a type of protein. They
have specific shapes that can recognize a specific
molecule. This is similar to how a key fits into a
lock. Enzymes can be used over and over again to
speed up reactions.
Transporters
These proteins are responsible for allowing materials
inside and outside of the cell. Transporters live in the
cell membrane. They usually function as a channel
or a pump to allow things to pass into or out of the
cell
Movers
Proteins are made up of chains
of amino acids. These chains
have weak and easily broken bonds. Because the
bonds are easily broken, they can shorten, lengthen,
and change shape in response to a change in energy.
When ATP is present, it can cause a protein to
'move'. The energy in ATP causes a bond to break
and the protein to take a 'step'. This can be repeated
through a long chain on proteins.
Supporters
Long chains of condensed proteins can form sheets
and tubes. These sheets and
tubes help support the cell
that make up the parts of
your body. This is similar
to a posts, cement, and nails
supporting a bridge.
Regulators
These proteins 'notice' when enough product
is made and stop the product from being
made. When enough of the final product is
made, a regulator protein shuts down the
assembly line.
Communicators
To work together effectively,
cells must be able to pass
messages back and forth.
Proteins act as a cell's chemical
messenger. A common example
of a communicator is a hormone.
Again, usually hormones are
studied in a class of their own, but most hormones
are in fact a type of protein
Defenders
When a virus or bacterium get into your body,
proteins act as a line of defense against the foreign
species. Antibodies are defender proteins that have a
specific shape that can recognize bacteria or viruses.
The antibodies then call for help from your immune
system
which
sends
cells to
come
and
destroy
the
foreign
species.
Understanding Protein
Pathways
Think back to our car analogy. We said that if the car is a cell,
then the parts under the hood are the proteins. They work together
to accomplish their jobs. It is important for scientists to
understand what proteins work together and how they work
together. It is common for scientists to map out these
relationships. This is called a protein pathway.
Sticking with our car analogy, lets work our way through a
protein pathway. First we have the ignition that activates the
engine. We know that the ignition and the engine (two proteins)
must work together. If the ignition is broken, the engine will not
turn on. We would model this relationship like this:
Ignition → Engine
The ignition protein has an arrow pointing towards the engine
protein. This means that the ignition
activated the engine.
Not everything in a car activates
something; some things inhibit an action
from taking place. For example, when you
hit the brakes, it inhibits the wheels from
turning. The brakes (a protein) job is to
stop the car. It accmplishes this by making the wheels stop
turning. If the brakes and the wheels did not work together
the car would not stop. We would model this relationship
like this.
Brakes ---| Wheels
The brake protein inhibits the wheel protein. This is
shown with the ---| symbol.
In our bodies, the protein pathways go from very simple to
extremely complex, but the same modeling system is used
for both. This helps scientists be consistent and show their
findings in a visually pleasing way. Here is an example of a
protein pathway modeled by scientists. This is an example
of a pathway with many different proteins working
together to accomplish their jobs. The yellow arrows are
showing activation, while the red arrows are showing
inhibition. (Don't worry- Our protein pathway only consists
of three proteins!)
A tricky thing about protein
pathways is visually how it
all works together. The
process of activation and
inhibition takes place very
quickly. Therefore, if a
protein inhibits a protein that
normally inhibits something,
that action will actually be
activated. For example in our
car the brakes inhibit the
wheels from turning. If
something were to suddenly
inhibit the brakes, lets say failing brake pads, the wheels would
keep turning. This is why it is important to keep in mind the
pathway as a whole. You can’t focus on one protein and
understand the affects on the cell. You must understand how each
protein works together to get a full picture. Keep this in mind
when you start working with a specific protein in the next section.
Hedgehog
In 1980 scientists discovered an important
protein in fruit flies. This gene was named
hedgehog. This protein was named because
when a fruit fly was missing this protein, it
had small pointy projections all over its
body and the scientists thought it resembled
a hedgehog.
After many years of research the job
of hedgehog is well known. In flies,
hedgehog is responsible for many
major developmental roles. It helps
the fly’s body form properly.
Hedgehog is in charge of placing the
legs and wings in the correct place,
as well as making sure the segments
of the fly’s body are in the correct
order. After extensive research in
fruit flies, scientists wanted to see if
a similar mechanism existed in
humans. Their curiosity paid off and Sonic Hedgehog was
discovered (shown right). This protein was the exact same
mechanism found in fruit flies but was in humans. This is a great
example of how working with a model organism allows scientists
to learn more about humans. Sonic Hedgehog is actually named
after the video game in combination with the hedgehog that was
already discovered in drosophila.