Our bodies are capable of a huge range of tasks,
from the ordinary breathing,
walking,
eating, to the extraordinary,
inventing new technologies,
sculpting pottery and running marathons. To achieve these goals, our bodies depend
on our organs, heart,
lungs,
brain,
et cetera,
working together.
Looking closer,
we see that each organ is made up of millions of individual cells working together.
Looking closer still,
we see that cells themselves are quite complex.
Every cell is essentially a tiny factory.
Overall,
they break down chemical fuel for energy and produce proteins and other molecules.
If we take one final step closer to look inside of a cell,
we can see these activities occur in compartments called organelles, or little
organs.
When you think of a factory,
you probably think of a large multi-storey building that makes stuff.
The building has protective exterior walls,
which is like the cell membrane or plasma membrane,
but the factory also has doors with swipe card entry to let in the right people and
supplies.
Similarly,
the plasma membrane,
which is made up of lipids and proteins,
is a selectively permeable barrier that allows only certain molecules to come in or
leave.
This usually means good things like nutrients and hormones,
although sometimes viruses can trick the cells and enter by similar mechanisms.
Once the materials are through the plasma membrane,
some end up in another membrane bound organelle,
called an endosome,
or an internal delivery service.
The endosome can deliver the material to many other organelles that we will learn about
soon.
The first compartment inside of our cells that we'll visit today is the most well known organelle:
the nucleus.
This is the combined IT department and CEO headquarters.
It is where critical information is stored and decisions are made.
Crammed inside of the nucleus of every single cell is two meters of
DNA, fibers that contain all of the information necessary for making your
proteins and for cell replication.
The nucleus,
like the plasma membrane and many other organelles,
is surrounded by a lipid membrane.
However,
it has relatively big pores called nuclear pores that allow RNAs
and some proteins to pass between the inside, the nucleoplasm, and the
outside, the cytoplasm.
The cytoplasm is the name for the entire space between the nucleus and the plasma membrane.
Inside of the nucleus sits the nucleolis,
an organelle within an organelle.
The nucleolis,
which is an example of a non membrane bound organelle,
is involved in making ribosomes, particles that synthesize proteins.
Now, let's look more at manufacturing.
Sitting just outside of the nucleus is the endoplasmic reticulum,
or ER, a network of sausage-like tubes extending through the
cytoplasm, that is involved in making proteins and lipids for cell
membranes.
Once these materials are made in the ER,
they are sorted, packaged and delivered to the cell's shipping department,
the Golgi apparatus.
The Golgi apparatus repackages these proteins in small shipping containers called
vesicles that get delivered to various other organelles and the plasma
membrane.
How does this delivery occur?
Analogous to the way in which packages can be taken around a factory along
hallways, vesicles are transported by motor proteins along long
protein fibres called microtubules and actin filaments,
which make up the cell's cytoskeleton.
In addition to making new products,
cells also have to get rid of expired products.
The main waste disposal department is an organelle called the lysosome,
which can degrade or recycle waste. Factories need an energy source to
keep all of this machinery working and so do cells. The food that we eat--
fat, carbohydrates and sugars-- is broken down by the cell and ultimately
needs to be converted to adenosine triphosphate, or ATP, for energy.
Let's take fat as an example.
The breakdown of fat is facilitated by peroxisomes,
which pass the products to mitochondria. A mitochondrian is the power plant that
takes a fuel derived from fat and converts it into ATP,
the main energy currency that cells use for their own activities.
As our tour concludes,
I hope that you can appreciate that the cell is a complex environment with many parts
working together to keep our bodies going.
Thus not surprisingly,
individuals with genetic disorders in one of the cells organelles often have
severe disease.
As scientists learn more about the intricate work of organelles and health,
stress and disease,
new therapies to combat these disorders may become possible,
and we can look forward to understanding more about how these tiny organelles make
our cells tick.