00:01
Hello and welcome to viruses.
00:04
We're going to dig a little bit deeper into
this fascinating subject, and at the
end of today's lectures, you should be able
to know how viruses are
cultivated and assayed.
00:16
You should be able to distinguish the seven
different types of viral genomes
and their structures.
00:23
And you should appreciate what information
is and is not encoded
in a viral genome.
00:32
Let's first start by talking a little bit
about how we study
viruses. Now you remember from our
introductory lecture that animal
viruses were discovered around the end of
the eighteen hundreds,
but for many years, these viruses could not
be routinely studied in
cells in culture.
00:54
They had to be studied, and laboratory
animals and laboratory animals of all
sorts were used.
00:59
Some of them are shown here.
01:01
But as you can imagine, this is not a
convenient procedure.
01:05
Plus, laboratory animals can differ from
experiment to experiment.
01:10
So it was very important to try and
determine how to grow viruses in cells, and
many scientists worked on that problem
before nineteen forty
nine. It was not possible to use cells in a
consistent and
reproducible way to study viruses.
01:27
But in that year, three scientists, Enders
Weller
and Robbins, working in the U.S., found that
they could propagate polio
virus, a human virus, in human cell
cultures.
01:41
Now they happen to use what we call primary
cultures from embryonic tissues.
01:46
But this experiment set a precedent for the
first time it was possible to
propagate a human virus in cell cultures.
01:53
This was a very important discovery for
which these researchers
receive the Nobel Prize in Medicine in
nineteen fifty four.
02:03
That discovery is with us today.
02:06
We since nineteen forty nine, we've been
able to study viruses in a variety of
cell cultures derived from different
sources.
02:15
For example, we can use primary cell cultures
where the tissue
is taken from a source it's minced up to to
produce
individual cells, and then it's put on a
plastic layer, in
addition covered with medium.
02:31
So on the left hand part of this slide, you
can see a photograph of
primary human foreskin fibroblast cells in
culture.
02:40
Human for skins are very easy to obtain
because when babies are
born, we often remove the foreskin.
02:47
It's thrown away in the hospital.
02:49
But if you're interested, you can obtain
them and produce primary cells like these.
02:53
This, of course, is not so convenient to use
on a routine basis.
02:57
So for that reason, we have what we call
cell lines.
02:59
And there are two examples of of these cell
lines shown on this slide.
03:03
One is a mouse fibroblast cell line.
03:06
It's called three T three, and then there is
a human epithelial cell
line. The famous HeLa cells, both of these
cells are what we call
immortal. They grow forever.
03:18
You can grow them over and over in the
laboratory, and then that makes it a lot
easier to do your experiments.
03:25
Now, the negative aspect of using a cell
line is that they're a little bit unusual.
03:30
They have far too many chromosomes, they're
a bit abnormal, and some of them are, in
fact, cancer cells.
03:36
So if this is a problem for your research,
we also have what we call diploid cell
lines like the W.I thirty eight cell line,
which is derived from human
embryonic lung. These have a normal number
of chromosomes.
03:49
They don't live forever, but they do live a
long enough time to make your experiments
convenient.