The different types of mutations

1. | MCAT | Khan Academy
Prepared by
Yousef Elshrek
THE DIFFERENT TYPES
OF MUTATIONS /
BIOMOLECULES

2. • In this lesson we're going to talk
about the different types of genetic
mutations that you would find in a
cell.
• But first, I want to review the
central dogma of molecular biology
and how the genetic information of
a cell is stored in the form of DNA,
which is then transcribed to form
RNA and then translated to
generate protein.
• Nucleotides from the 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.

3. • Now, if you mutate one
of the nucleotides on
DNA, like let's say
turning this thymine-
based into an adenine-
based, then that will
affect the RNA sequence
and ultimately the
protein that follows.
• So, we say that
mutations are mistakes
in a cell's DNA that
ultimately lead to
abnormal protein
production.

4. • WHAT ARE THE
DIFFERENT TYPES
OF MUTATIONS?
• The first type of mutations
are called point
mutations
(substitutions).
• If we write out a random
sequence of DNA, which
is just a repeating pattern
of CTC, which would
code for a repeating
sequence of GAG in the
RNA strand, and finally, a
protein sequence of three
glutamate amino acids.

5. • So, a point mutation is
when one of our DNA
bases is replaced with
another.
• In this example, a
thymine-based is being
replaced with an
adenine-based, which
leads to a change in one
RNA nucleotide and
ultimately a change in
one amino acid

6. • Another type of mutation is
called frame-shift, which
works a little differently.
• So, first I'll write out the same
DNA, RNA, protein sequences
from before, but now, instead
of changing one base to
another, I'm going to add one to
the sequence, and here I've
thrown in this extra cytosine
base that I've written in blue.
• Point mutation Frame shift mutation

7. • Now, naturally, this change
would lead to an additional
guanine base being in the
resulting messenger RNA
sequence, but what's interesting
is that this mutation will change
the reading frame of the RNA.
Point mutation Frame shift mutation

8. • Remember that RNA is read in
groups of three or codons when
being translated to form
protein, but now, since we've
added an extra G here, all the
codons coming after that extra
G will look a little differently.
• Now, instead of having three
GAG codons, we've swapped
out two for GGA codons.
• This means that two of our
amino acids in the final protein
will be changed, and in this
example, they'll be changed
from glutamate to glycine.
Point mutation Frame shift mutation

9. • So, you can see that
frame-shift mutations
usually have more
significant effects on the
final protein than point
mutations do.
• Now, it's important to
recognize that both
mutations are classified
and named for how they
affect the cell's DNA
structure and aren't
really named for how
they affect the resulting
protein

10. • Now, our next type of mutations
are non-sense mutations and
missense mutations.
• Let's say we have a DNA sequence
that normally generates RNA and
codes for a cysteine amino acid.
• A non-sense mutation is any
genetic mutation that leads to the
RNA sequence becoming a stop
codon instead.

11. • Now, missense mutations are a
little different, and they're any
genetic mutation that changes an
amino acid from one to another.
• So, in this example, our mutation is
changing the resulting amino acid
from a cysteine to a tryptophan

12. • Now, you can see that non-sense
mutations probably affect the
resulting protein a lot more than
missense mutations do, since that new
stop codon that we're creating could
chop off a huge section of the protein,
instead of just changing one amino
acid to another.
• So, now we can divide the missense
mutations even further into a bunch of
smaller categories.
• Silent mutations are when the
mutation doesn't affect the protein at
all.
• Since many different RNA codons can
code for the same amino acid, it's
possible that the mutation might not
affect the protein at all.

13. • Since many different RNA
codons can code for the same
amino acid, it's possible that the
mutation might not affect the
protein at all.
So, in this example, CCA, CCG,
CCT, and CCC in the section of
DNA will all end up coding for
glycine.

14. • So, if you change the third base, 0it
wouldn't affect the final protein.
• Conservative mutations are where
the new amino acid is of the same
type as the original.
• So, here I have a glutamate and an
aspartate, 04:08 which are both
acidic amino acids.
• So, a mutation that swapped out an
aspartate for a glutamate would be
a conservative mutation.
• Finally, a nonconservative mutation
is one with a new amino acid is of a
different type from the original.

15. • So, here we have a serine amino
acid, which is a small polar
amino acid, being replaced with
phenylalanine, which is a large,
nonpolar, aromatic amino acid,
and this would be an example of
a nonconservative mutation,
since serine and phenylalanine
are different types of amino
acids.

16. • Now, I'll point out again that all of
these mutations are classified and
named for how they affect the
resulting proteins and aren't really
named for how they affect the cell's
DNA.
• So, let's look at a quick example.
• Sickle cell disease is a disorder
where hemoglobin or Hb, which is a
protein found in human blood, is
mutated into a less active form,
which we're going to call HbS, and it
result from a single glutamate
residue being converted into a valine
residue.

17. • Now, we can classify this
mutation as a point mutation,
since only one DNA base is
affected, but we can also say that
it's a nonconservative missense
mutation, since glutamate is
being swapped out for valine,
and the two are different types of
amino acids, since glutamate is
an acidic amino acid, and valine
is a nonpolar one.

18. • WHAT DID WE LEARN?
• Well, first we learned that mutations
originate at the DNA level, but show their
effects on the protein level, and second, we
learned that we can, classify different types
of mutations by either their effects on DNA
or their effects o protein.
• In reference to DNA, we have point and
frame-shift mutations, and in reference to
protein, we have missense and non-sense
mutations.
• SUMMARY
1. Mutations originate at the
DNA at the DNA level but
show their effect at the
protein level.
2. Mutations can be classified
by their effects on DNA or
on protein

19. • https://www.youtube.com/watch?v=xYOK-yzUWSI