Hey wait up for me!
ow
Are you ok
I think I just tripped over a root oh my knee
your body is an incredible
living system made up of
billions of cells
we are following blood cells as
they're propelled through a blood vessel
toward the boy's injured knee
if you are hurt your cells work together to repair the damage
they communicate using their own language of chemical signals
now we've arrived at the wound site blood cells are flowing out of the broken blood vessel ahead
moments after an injury
these blood cells and cell fragments started a form of mesh-like clot
many different types of cells are involved in tissue repair
the flat light-colored cells
are fibroblasts
Early in the healing process
fibroblasts multiply and
produce proteins that help to repair the damage
The smaller dark cell fragments
between the fibroblasts are platelets
when activated
platelets release a stream
of protein messengers called
growth factors to stimulate cell growth and tissue repair
to see how growth factor from a platelet signals a nearby fibroblast cell
we need to swoop in close to the rippling fibroblast surface
fibroblasts like all your cells
have a fluid outer membrane that regulates the flow of molecules
in and out
the gray structures sticking out of the cell membrane are
receptors for incoming signals
when the growth factor from the platelet shown in purple and blue
encounters a matching receptor
it binds to it
a second receptor protein joins in
making the growth factor fit
like a key in a lock
the binding of the growth factor causes the receptor to change shape
this change in the protein
conducts the signal through the membrane
and into the cell's interior
the cytoplasm
you'll see this better
from inside the cell
beneath the cell membrane you see the gray receptor end surrounded by pink fibers
these structures help to give the cell its shape and a range of messenger
proteins that will carry the signal through the cytoplasm
while active
as shown by the yellow flashes of light the ends of the receptor interact with the
messenger proteins
Now we'll watch the action again from our position in the cell's cytoplasm
the growth factor binds the receptor proteins outside the cell drawing the
receptor ends together the signal is transmitted through the cell membrane
and each new protein is activated in turn if you look closely
you can see the proteins change shape as they become activated with the
signal
each step of a pathway is under tight control to ensure the correct message is relayed
for example as this white protein accepts the signal the blue protein
comes in to deactivate
the red one
let's follow the white protein on its journey through the cytoplasm
toward the center of the cell
as we follow the signal to the nucleus
you'll see it passed from messenger to messenger
the first exchange is with this brown protein
the second will be with a purple protein in a few seconds time
although we were only following one path
a single cell has many different ways to transmit signals through cytoplasm
the fibers shown in green are part of the cytoskeleton
like the pink fibers you saw before
these give the cell shape and
help to organize its contents
crawling along the fibers
are motor proteins that
reshape the cytoskeleton and help this fibroblast cell to move
on our way
we will encounter other structures in the cytoplasm
known as organelles
on the right
you see glowing organelles called mitochondria
which generate energy for the cell
the activated protein passes by a network of membranes here in light brown
known as the endplasmic reticulum
the protein is transported into the nucleus through a pore in the nuclear membrane
the nucleus contains tightly wound coils of DNA
shown in green
the protein messenger passes the signal to two other molecules that team up to
locate a specific gene along the DNA
in this case
the gene carries the information to make a growth factor
other molecules then unwind
a small section of the DNA molecule
and allow an enzyme called RNA polymerase shown in brown
to make an RNA copy of the gene
the copy called messenger RNA here in light green is packaged with a set of
carrier proteins and leaves the nucleus
the cell will use this copy to make the growth factor