Voiceover: Today I'm going to give you a quick
introduction into genetic mutations.
But first, let's go over the central dogma
of molecular biology, which is just the idea
that genetic information in a cell
is formed in the form of DNA.
This DNA is used to generate complimentary RNA
through a process called transcription.
That RNA is then used to synthesize a corresponding
protein through the process of translation.
Looking at a quick example,
our short DNA strand here
will be used to generate an RNA stand.
Remember that A pairs with U or T
and C pairs with G.
Next, our RNA will be used to generate
protein through translation.
Remember that during this process,
RNA nucleotides are read in groups of three,
called codons, in order to generate
corresponding amino acids.
Just very generally, we say that mutations
>>have the affect of making this synthesized
protein not turn out quite right.
I'm going to give a quick shout-out to sickle-cell disease,
which is an example of a disease
that's caused by a genetic mutation.
You may remember that there is a protein
in red blood cells called hemoglobin,
which we can also call Hb.
Hemoglobin in a protein that coordinates
to iron ions in order to hold onto oxygen molecules
and transport them throughout the body.
The mutation that causes sickle-cell disease
results in a mutated form of hemoglobin
called HbS being formed, where the S is for the word sickle.
The difference between normal hemoglobin
and HbS is that one glutamate amino acid residue
is being replaced with a valine amino acid residue.
This small change results in all of these mutated
HbS proteins aggregating together in a red blood cell,
which makes it very difficult for that red blood cell
to transport oxygen effectively.
Just a side point, remember that red blood cells
are initially generated from hematopoietic stem cells
through a process called hematopoiesis.
Where are mutations found,
and how do they come up in the first place?
Let's look at a couple of different possible mistakes
that could lead to an incorrectly produced protein.
First, we'll see what happens if a cell
makes a mistake during translation.
We'll stick with our example
of sickle-cell disease from before.
Let's say that we have this sample piece of DNA
with three nucleotides from the gene
coding for hemoglobin.
This DNA is transcribed to form
the complimentary RNA sequence GAG.
That GAG would normally correspond
to a glutamate residue during translation,
but a mistake during translation might lead
to a valine residue being translated instead
to produce the mutated hemoglobin
associated with sickle-cell disease.
But notice that if a mutation happens
during translation, the cell will only
produce one mutated hemoglobin, or HbS,
for each overall mistake.
Since cells are making tons and tons of hemoglobin,
just one mutated protein might not have
that big of an effect on the cell.
So we can say that mistakes during translation
probably don't cause mutations
like the one associated with sickle-cell disease.
Next, we'll look at mistakes during transcription.
Again, we have our CTC piece of DNA,
which would normally make GAG on RNA,
but maybe a mistake occurs
which leads to the transcription to a GUG instead,
which would then code for the valine
associated with mutated hemoglobin.
If this mistake occurred, the cell would
only make a few mutated hemoglobins for each mistake
since an individual strand of messenger RNA
will only be translated a couple of times
before being degraded.
>>So we can say that mistakes during transcription
probably don't cause mutations like the one
associated with sickle-cell disease.
Finally, we'll look at mistakes in the DNA strand.
If our CTC in DNA is mistakenly turned into a CAC,
then our corresponding RNA from transcription
will be changed and ultimately a valine
would be produced instead of a glutamic acid.
Now, since a cell's DNA stores all of its
genetic information, that mistake would lead
to all future hemoglobins produced
from that gene being mutated.
So overall, we can say that mutations will
usually result from mistakes in a cell's DNA
and not from the RNA or the protein.
So where do these types of mutations come from?
There are two ways a person can get a genetic mutation.
The first is that they inherit it from their parents.
Remember that DNA is passed down
from parents to offspring,
so if we have a mutated father here,
then there's a good chance that at least one
of his kids will inherit that mutated gene
the same way that the child might inherit
any amount of that parent's DNA.
The other possibility is that the mutation
will come on spontaneously,
which is where a person suddenly gets
a mutation in their DNA without their parents
having had the same mutation.
Spontaneous mutations can come from many different sources,
with just a few examples being
from DNA replication errors,
environmental factors like certain poisons.
It's also possible that genetic mutations
can come on entirely randomly.
What did we learn?
First we learned that mutations originate
at the DNA level, and not the RNA or protein level.
The effects of the mutation, like the example
we gave of sickle-cell disease,
are found with problems with the proteins
that are ultimately expressed by the mutated DNA.
Now, like every rule, there are a couple
of exceptions to this one,
but we can say that the effects of a mutation
are usually found at the protein level.
Finally, we learned that mutations
are either inherited from a parent,
or come on entirely spontaneously.