Microorganisms and Health [6]: Antigenic Variation (A Level Biology)


Uploaded by freeeschool on 02.09.2012

Transcript:
A Level Biology: Microorganisms and Health 6 – Antigenic Variation
Hi! Welcome to my sixth video on the series about Microorganisms and Health. Today, we
are going to be looking at Antigenic variation.
Many of the problems particularly with viruses are the fact that they can mutate and change.
If we look at a typical virus, for instance, this might represent a flu virus and on the
surface of this flu virus, you have the antigens represented by these yellow triangles. If
you got infected with the flu, what you would expect is a normal immune response and so
for you to produce the relevant antibody. If you remember back to previous videos, these
antibodies need to have a specific shape that is complementary to the antigen shape; a bit
like this one.
So what then can end up happening is the antibody can bind to the antigen and being able to
clump lots of these viruses together. At this point, what happens is you then build up memory
cells within your system so that if you are exposed to this pathogen again, you have a
very, very quick secondary response and a very, very large one and hence, you won’t
get ill again.
But the problem comes, specifically with things like flu, is in the fact that they mutate
very, very readily. By mutate, I mean, there is a genetic change. This mutation can happen
when it is making a copy of itself and because some viruses can do this quite sloppily, they
won’t make an exact copy and they will make mistakes within the DNA. The issue here is
that if there is a mutation, and this mutation happens to change the actual shape of the
antigen, then that can be a huge benefit for the microorganism.
However, I should stress that most mutations are not a benefit to the actual virus or to
the microorganism. Most will actually result in it failing and therefore, not promoting
survival. But essentially, if there is one mutation that is beneficial, then it is likely
to pass on. In the case of this mutation, this one is a clear benefit. The antigen has
changed shape and now, our antibody no longer is able to affix to it and therefore, we need
to go through the entire process where we need to locate a specific B cell to actually
produce the specific antibody.
That may take some period of time in order to do that. You may eventually find it. But
if this disease is one which is very, very dangerous and if that latent period is much
too long, then that can cause serious issues down the line.
In the case of the flu virus, it can cause damage to your cells and if it causes damage
to enough cells, it can actually result into serious illness and specifically in older
people or younger people, can result actually in death.
This is part of the flu survival mechanism, the fact that it is able to survive for long
periods of time. It is down to the fact that it mutates readily and changes. Therefore,
our immune system has to catch up constantly. It is a constant arms race between our white
blood cells and the invading microorganisms like flu.
Another one of the survival mechanisms for the flu virus is the fact that it can combine
with other strains of flu and produce new, novel strains. So in the case of these two,
it is quite simplistic here with two different shapes, but they’re able to combine to produce
new antigens and a different strain of the flu virus. Hence, we have outbreaks of avian
and swine flu in this country.
The fact that the flu mutates so readily is the reason why we need a new vaccination every
year. We end up having to fight a different strain of flu from year to year. So by using
the previous year’s vaccination, it would be completely ineffective against the current
flu virus.
In summary, when a pathogen reproduces, it can mutate and so this is true for all the
different types of pathogen; be it fungi, bacteria or viruses. This mutation mostly
would be non-beneficial but the ones that are beneficial could potentially lead to a
change in antigen shape and this means that the memory cells that you built up in resistance
to these specific pathogens are no longer useful.
Also, viruses can not only mutate in that fashion but they can also combine with different
strains of viruses and therefore, produce a new strain, of which the antibodies that
you have produced are useless.
[end of audio – 04:43] A Level Biology: Microorganisms and Health
6 – Antigenic Variation Page…1