Voiceover: Today we're going to talk about the overall effects of a genetic mutation and how mutations impact the organism as a whole. But first, I want to review the central dogma of molecular biology, and how genetic information
in a cell is stored in the form of DNA,
which is then transcribed to form RNA, which is then
translated to form protein. Nucleotides from DNA are transcribed to their complementary forms on RNA, which are then read as codons, or groups of three, to code
for specific amino acids in a larger protein. If you mutate one of
the nucleotides on DNA, like turn this thymine
base into an adenine base, then that will affect the RNA sequence, and ultimately the protein that follows. We say that mutations
are generally mistakes in a cell's DNA that lead to abnormal protein production. So are mutations good, or are the bad, and what kind of effect do they have on the affected organism? Well, there really isn't a good answer to this question at all. There are many, many
different types of mutations out there that can result
in big structural changes, like the little pictures
I've drawn out here, or may result in little, subtle changes, that might go completely unnoticed. It's very difficult to call a mutation good or bad though,
since it really depends on a huge number of things,
including the environment that the organism lives in. Let's look at an example
of a good mutation. The bacteria Streptococcus Pneumoniae is the bacteria that you typically see associated with pneumonia. One of the more popular
treatments for pneumonia is giving the infected
person an antibiotic like penicillin, which would
help kill all of the bacteria and get rid of the disease. But sometimes, you can find some mutated Streptococcus bacteria, that
will have a special trait that makes them resistant to penicillin, and now penicillin won't
kill them as easily as it'll kill the bacteria
without the mutation. We call this a good mutation because the bacteria are
living in a human host, where they are likely to
encounter this deadly penicillin. Being resistant to
antibiotics like penicillin would then be beneficial to the bacteria. Just to clarify, I'm
calling this a good mutation for the bacteria, not really
for the human infected, since it'll be harder for them
to get rid of the bacteria that are resistant to certain antibiotics. Let's look at an example
of a bad mutation. The disease cystic
fibrosis is usually caused by a mutation in the CFTR gene. I'm not really going to go into detail about how this mutation
actually hurts you, but I'll leave you with the idea that what it does is it makes the mucus that you would find in a person's lungs really, really thick,
which makes it really hard for people affected with
the disease to breathe. In general, we can say that a mutation causing cystic fibrosis
would be a "bad" mutation. But mutations aren't strictly
good or strictly bad. In fact, there are some mutations that can cause some favorable and some disadvantageous effects. Sickle-cell disease
results from a mutation in a protein called hemoglobin, that you'd find in red blood cells. This mutation turns hemoglobin into a much less functional
form, which we'll call "HbS". It's much less efficient at moving oxygen around the human body. Another effect of sickle-cell disease is it makes the diseased person
less susceptible to malaria. Malaria is a parasite
that grows and multiplies in red blood cells, and can
have a lot of nasty effects on the host organism. The malaria parasite
can't really grow as well in red blood cells that are affected with sickle cell disease. In this case, the mutation associated with this disease has one bad effect, which is that the HbS isn't as good at carrying
oxygen around the body, but also a good effect, in that it makes it less likely that the diseased person
will be affected by malaria, since they can't grow as well in the human's red blood cells. What did we learn? First we learned that
the effects of a mutation will usually, but not always, appear at the protein level. There are some exceptions to this rule. Second, we learned that genetic mutations can have advantageous, deleterious, or neutral effects, depending
on the type of mutation, the environment that the
infected organism lives in, as well as a multitude of other factors.