Main content
High school biology
Course: High school biology > Unit 6
Lesson 2: RNA and protein synthesis- Molecular structure of RNA
- DNA replication and RNA transcription and translation
- Intro to gene expression (central dogma)
- The genetic code
- Impact of mutations on translation into amino acids
- RNA and protein synthesis review
- Transcription and translation
- Codons and mutations
© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice
Impact of mutations on translation into amino acids
AP.BIO:
IST‑2 (EU)
, IST‑2.E (LO)
, IST‑2.E.2 (EK)
Using an amino acid translation table to understand the impact of point and frameshift mutations.
Want to join the conversation?
what type of diseases can you get from bad mutations?(3 votes)
Well, a good example of a disease that you could get from a bad mutation, is Sickle Cell Anima. Sickle Cell Anima is caused when 1 codon (DNA code unit) is inherited in its mutated version from both parents. That one single error in the many, many codons that code a red blood cell, causes a whole slew of errors in the creation of the body’s red blood cells. The codon in question causes the misplacement of a single atom in the hemoglobin protein, that causes it fold over during its production. This causes the new red blood cells to sickle shaped (Like a ( shape), thus the name, and causes numerous malfunctions within the cell. Sickle Cell Disease is just one example of the many bad things that one can get from a bad genetic mutation and it is very interesting that one tiny little error in the DNA code could have such a tremendous effect in a person. Other examples of genetic disorders include Muscular Dystrophy, Down’s Syndrome, and Cystic Fibrosis. I hope I answered your question. :)(12 votes)
When does mutation normally happen,in birth,during development or other things?(3 votes)
During development, as a fetus, when the body is replicating cells at a rapid rate. Although environmentally caused mutations (ie. cancer) are also common(5 votes)
- Is a mutation like a mistake in the DNA? In my bio class they said that mistakes in translating DNA were very rare like 1 in a billion, so is a mutation like this or is it different? Also how can an extra nucleotide get inserted or changed, how does this process specifically happen?(0 votes)
Yes a mutation is a mistake in the DNA, compared to what it should be. It is rare for it to happen, but there is also a lot of DNA in your cells. In a diploid human cell, there are over 6000 million basepairs of DNA. And when that is copied for cell division, mistakes can happen. As you say, this may be only one in a billion, but with billions of bases, you get some mistakes. As well as copying into the wrong base, maybe the polymerase doing the copying will slip and skip a base or so. Another way that mutations can happen if the DNA gets damaged and isn't repaired properly. This damage could be from x-rays, UV radiation, or mutagenic chemicals. They tend to cause different types of damage, which is repaired in different ways. Sometimes DNA is damaged in a way that both strands break, and the cell will try to glue them back together. However, this is not always perfect and mistakes can be introduced. There may be bases missing, especially if the nucleotides at the DNA ends were damaged so they couldn't be stuck straight onto each other.(6 votes)
What is codons and mutations? I can't get to fully understand.(2 votes)
Codons are a group of three nucleotides, while mutations are mistakes in a cell's DNA where certain nucleotides are either swapped, inserted, deleted (I think there are other examples too but these are the main ones), which can either have small effects (example: changing one amino acid) or huge effects (example: changing the protein permanently). Hope this helped!(2 votes)
When would you use U-A?(1 vote)- So do point mutations include frameshift mutations? Because I searched point mutations up and it is apparently a change in a single nucleotide of DNA (swap, insertion, deletion), and a frameshift seems to be an an insertion or deletion that changes the reading frame of the DNA.(1 vote)
- How does a frameshift mutation occur naturally? Considering the fact that it would need a sizable amount of energy to actually insert a nucleotide , as it involves breaking the strand itself, so where does this energy come from?(1 vote)
How does a frameshift mutation happen in DNA replication? If DNA Polymerase III adds or deletes a base, won't it notice that the rest of the base pairs that it creates downstream from there are incorrect?(1 vote)
Examples of each type of mutation in humans and plants, please.(1 vote)
What is the likeliest outcome of a base substitution mutation
within an intron?(0 votes)
Video transcript
- [Instructor] So, let's start looking at a short sequence of DNA, and the letters I'm going to use, these are the shorthands for
the various nucleotide bases that make up a sequence of DNA. So, let's say that I have some thymine, thymine, cytosine,
guanine, cytosine, thymine, adenine, thymine, thymine, and let's throw another thymine in there. So, that would be our sequence of DNA, and what would be the
corresponding sequence of RNA that it would be transcribed into? If you remember this from previous videos, pause this video and
try to figure that out. Well, the key thing to appreciate is, if we're talking base pairs in DNA, adenine pairs with thymine, cytosine pairs with guanine, but if we're talking
about pairing into RNA, well then, instead of thymine in the RNA, you would have uracil. So, the RNA here is, well, the thymine in
the DNA would correspond to an adenine in the RNA, adenine, guanine, cytosine, guanine, adenine, and now, since this is an RNA strand, instead of having a
thymine right over here, this would be a uracil,
adenine, adenine, adenine. So, this process that we just did, this is transcription. Transcription, transcription from DNA, DNA to RNA. Now, the next step, if we're talking about the whole process of, how
does this information actually have an effect on the
body, is we're gonna go from the RNA and translate that into a protein. And the way we do that, we've
seen this in previous videos, is every three of these
bases, that's a codon, and it codes for a particular amino acid. Now, to figure out what
amino acid it codes for, we look at an amino
acid translation table, and there's different
types that you might see. This is the most typical type, so the first base is A, second base is A, third base is G. First base, A, second base, A, we're in this cell, third base is G, and so that will code for
the amino acid, lysine, so we could write l-y-s,
short for lysine here. And we could've also gotten that from a different type
of translation table. For example, you might see a circular
one that looks like that, but we would've gotten the same result. AAG, start at the center, AAG codes for lysine. Then, the next codon,
and if you're getting as excited about this as I am, I encourage you to pause this video and try to keep translating this. The next codon is CGA. CGA, arginine. Arginine, and then the next one is UAA. UAA. Well here, they have this
little black, circular dot, what does that mean? Well, that means stop codon, and sometimes they'll just
write the word stop there. So, this is stop. There is not an amino acid called stop, this actually signals
to, and this is happening at a ribosome, this is signaling for the translation process to stop, this is the end of our amino acid chain, of our polypeptide chain. And so, we will stop right over there. But now, let's do some interesting things. Let's think about situations where there are mutations,
where some of these bases, maybe something gets inserted, maybe something gets deleted, maybe something gets swapped out. And so, let's start with what's known as a point mutation, so let's say this C gets swapped out for an A. Well, if that happened,
then on the RNA strand, all of a sudden this would be a uracil, and if that is a uracil, this
AAG would still be there, coding for lysine, but this
second codon is now different. What would it now code for? Well, CUA. CUA, it'll now code for
leucine instead of arginine. Leucine, l-e-u. This is fairly typical for
a substitution mutation. It might change a particular amino acid, but sometimes, it could
be more significant. For example, if this G was swapped out for an A, then this C on the RNA would then be a U, and then what would happen? Well, this first codon
would still code for lysine, but the second one would be UGA. UGA. Now, all of a sudden, it
codes for a stop codon, and so, the actual translation
process would stop, which could be a very, very big deal if this DNA sequence, if the normal, non-mutated polypeptide had to keep going on, and on, and on. Over here, it just happened
to have a stop codon next, but you could imagine, if
they had just, you know, another thousand codons before the end, but all of a sudden, you had a
point mutation to stop early, that would significantly
affect the protein that it's coding for. Now, another type of
mutation that typically has a fairly significant affect is a frameshift mutation,
and that's where something gets inserted or deleted
and shifts everything. So, for example, instead of the A being swapped in for the G, what if the A got inserted here? So then, our sequence
would look like this. T-T-C, and then we have A, and
then you have G-C-T, G-C-T-A-T-T-T. So, what just happened here, this was our original sequence,
but the A got inserted here, it didn't replace the G, and so everything got shifted to the right. Now, what are we coding for? Well, when we transcribe
to RNA, this will be A-A-G-U-C-G-A-U-A-A-A, and now this first codon
still codes for lysine, we've seen that multiple times. But, what about this second codon? This second codon over here, UCG. UCG, that's serine, we got a different amino acid. And what's interesting is, it's not just that one amino acid is changing, we're gonna see that keeps happening. So now, we have AUA. AUA. Here, we have isoleucine. So, isoleucine, right over here, which is different than what we had before, we
don't have a stop codon anymore, and we would keep going on and on. And so, you could imagine
a frameshift mutation where you either insert something or you take it out so that
the whole frame gets shifted, can have a dramatic impact on what it will transcribe and then translate for. Now, lucky for us, even though mutations are always going on, there are
many proofreading mechanisms in biological systems to
make them less frequent than they otherwise would be, and people are still understanding how these proofreading
mechanisms fully happen. Another thing to appreciate is, we often associate a mutation as being equal to a bad thing, and often times, it is a bad thing. What used to be a functional protein may no longer be a functional protein because the amino acids,
the coding got stopped short or there was a frameshift mutation that's just coding for
completely different things. So, sometimes it could be very bad, and some diseases actually are caused by strange mutations
like that, that show up. Often times, the mutation
might not be a big deal. Maybe something gets swapped out, maybe only one amino acid changes and it doesn't really change the ability of the protein to do its job, in which case it doesn't matter, but every now and then,
a mutation can actually be a good thing. In fact, we need the mutation in order to have variation in a population, and variation is what natural selection and evolution run off of. If you don't have variation, then you're not going
to have different things that get selected in
different environments and you're not going to have
that gradual change over time. So, a big picture, hopefully
you got a better appreciation for how transcription,
and then translation, let me write that down. And then, so that's
transcription from DNA to RNA, and then this is translation. Translation from RNA to protein, to protein. We have appreciation of how that happens, we got appreciation of how to
use these translation tables, but also how either a point mutation or a frameshift mutation
can eventually affect the protein that gets coded for.