All living things are made of cells. In the human body, these highly efficient units
are protected by layer upon layer of defense against icky invaders like the cold virus.
Shannon Stiles takes a journey into the cell, introducing the microscopic arsenal of
weapons and warriors that play a role in the battle for your health.
You're in line at the grocery store when, uh oh, someone sneezes on you.
The cold virus is sucked inside your lungs and lands on a cell on your airway lining.
Every living thing on Earth is made of cells, from the smallest one-celled bacteria
to the giant blue whale to you. Each cell in your body is surrounded by a cell
membrane, a thick flexible layer made of fats and proteins, that surrounds and
protects the inner components. It's semipermeable, meaning that it lets some
thing pass in and out but blocks others. The cell membrane is covered with tiny
projections. They all have functions, like helping cells adhere to their neighbors
or binding to nutrients the cell will need. Animal and plant cells have cell
membranes.Only plant cells have a cell wall, which is made of rigid cellulose
that gives the plant structure. The virus cell that was sneezed into your lungs
is sneaky. Pretending to be a friend, it attaches to a projection on the cell
membrane, and the cell brings it through the cell membrane and inside.
When the virus gets through, the cell recognizes its mistake. An enemy is inside!
Special enzymes arrive at the scene and chop the virus to pieces.
They then send one of the pieces back through the cell membrane,
where the cell displays it to warn neighboring cells about the invader.
A nearby cell sees the warning and immediately goes into action.
It needs to make antibodies, proteins that will attack and kill the invading virus.
This process starts in the nucleus. The nucleus contains our DNA, the blueprint
that tells our cells how to make everything our bodies need to function.
A certain section of our DNA contains instructions that tell our cells how to make
antibodies. Enzymes in the nucleus find the right section of DNA, then create
a copy of these instructions, called messenger RNA. The messenger RNA leaves
the nucleus to carry out its orders. The messenger RNA travels to a ribosome.
There can be as many as 10 million ribosomes in a human cell, all studded along
a ribbon-like structure called the endoplasmic reticulum. This ribosome reads the
instructions from the nucleus. It takes amino acids and links them together one by
one creating an antibody protein that will go fight the virus. But before it can do
that, the antibody needs to leave the cell. The antibody heads to the golgi
apparatus. Here, it's packed up for delivery outside the cell. Enclosed in a bubble
made of the same material as the cell membrane, the golgi apparatus also gives
the antibody directions, telling it how to get to the edge of the cell. When it gets
there, the bubble surrounding the antibody fuses to the cell membrane. The cell
ejects the antibody, and it heads out to track down the virus. The leftover bubble
will be broken down by the cell's lysosomes and its pieces recycled over and over
again. Where did the cell get the energy to do all this? That's the roll of the
mitochondria. To make energy, the mitochondria takes oxygen, this is the only
reason we breathe it, and adds electrons from the food we eat to make water
molecules. That process also creates a high energy molecule, called ATP which
the cell uses to power all of its parts. Plant cells make energy a different way.
They have chloroplasts that combine carbon dioxide and water with light energy
from the sun to create oxygen and sugar, a form of chemical energy. All the parts
of a cell have to work together to keep things running smoothly, and all the cells
of your body have to work together to keep you running smoothly.
That's a whole lot of cells. Scientists think there are about 37 trillion of them.
1. What is a cell?
2. How do cells beat the virus?
3. Cells need energy to perform all of their functions.
Where in the cell is energy made?