The different types of mutations

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.
•Inthisexample,a
thymine-basedisbeing
replacedwithan
adenine-based,which
leadstoachangeinone
RNAnucleotideand
ultimatelyachangein
oneaminoacid

6. •Anothertypeofmutationis
calledframe-shift,which
worksalittledifferently.
•So,firstI'llwriteoutthesame
DNA,RNA,proteinsequences
frombefore,butnow,instead
ofchangingonebaseto
another,I'mgoingtoaddoneto
thesequence,andhereI've
throwninthisextracytosine
basethatI'vewritteninblue.
•Point mutation Frame shift mutation

7. •Now,naturally,thischange
wouldleadtoanadditional
guaninebasebeinginthe
resultingmessengerRNA
sequence,butwhat'sinteresting
isthatthismutationwillchange
thereadingframeoftheRNA.
Point mutation Frame shift mutation

8. •RememberthatRNAisreadin
groupsofthreeorcodonswhen
beingtranslatedtoform
protein,butnow,sincewe've
addedanextraGhere,allthe
codonscomingafterthatextra
Gwilllookalittledifferently.
•Now,insteadofhavingthree
GAGcodons,we'veswapped
outtwoforGGAcodons.
•Thismeansthattwoofour
aminoacidsinthefinalprotein
willbechanged,andinthis
example,they'llbechanged
fromglutamatetoglycine.
Point mutation Frame shift mutation

9. •So,youcanseethat
frame-shiftmutations
usuallyhavemore
significanteffectsonthe
finalproteinthanpoint
mutationsdo.
•Now,it'simportantto
recognizethatboth
mutationsareclassified
andnamedforhowthey
affectthecell'sDNA
structureandaren't
reallynamedforhow
theyaffecttheresulting
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,missensemutationsarea
littledifferent,andthey'reany
geneticmutationthatchangesan
aminoacidfromonetoanother.
•So,inthisexample,ourmutationis
changingtheresultingaminoacid
fromacysteinetoatryptophan

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. •SincemanydifferentRNA
codonscancodeforthesame
aminoacid,it'spossiblethatthe
mutationmightnotaffectthe
proteinatall.
So,inthisexample,CCA,CCG,
CCT,andCCCinthesectionof
DNAwillallendupcodingfor
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,herewehaveaserineamino
acid,whichisasmallpolar
aminoacid,beingreplacedwith
phenylalanine,whichisalarge,
nonpolar,aromaticaminoacid,
andthiswouldbeanexampleof
anonconservativemutation,
sinceserineandphenylalanine
aredifferenttypesofamino
acids.

16. •Now,I'llpointoutagainthatallof
thesemutationsareclassifiedand
namedforhowtheyaffectthe
resultingproteinsandaren'treally
namedforhowtheyaffectthecell's
DNA.
•So,let'slookataquickexample.
•Sicklecelldiseaseisadisorder
wherehemoglobinorHb,whichisa
proteinfoundinhumanblood,is
mutatedintoalessactiveform,
whichwe'regoingtocallHbS,andit
resultfromasingleglutamate
residuebeingconvertedintoavaline
residue.

17. •Now,wecanclassifythis
mutationasapointmutation,
sinceonlyoneDNAbaseis
affected,butwecanalsosaythat
it'sanonconservativemissense
mutation,sinceglutamateis
beingswappedoutforvaline,
andthetwoaredifferenttypesof
aminoacids,sinceglutamateis
anacidicaminoacid,andvaline
isanonpolarone.

18. •WHATDIDWELEARN?
•Well,firstwelearnedthatmutations
originateattheDNAlevel,butshowtheir
effectsontheproteinlevel,andsecond,we
learnedthatwecan,classifydifferenttypes
ofmutationsbyeithertheireffectsonDNA
ortheireffectsoprotein.
•InreferencetoDNA,wehavepointand
frame-shiftmutations,andinreferenceto
protein,wehavemissenseandnon-sense
mutations.
•SUMMARY
1.Mutationsoriginateatthe
DNAattheDNAlevelbut
showtheireffectatthe
proteinlevel.
2.Mutationscanbeclassified
bytheireffectsonDNAor
onprotein

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