There are different types of genetic mutations that can occur in a cell. Point mutations involve the replacement of one base with another.Frame-shift mutations occur when a base is added or removed from the sequence. Non-sense mutations create a stop codon, which can prevent the protein from being produced entirely, while missense mutations result in the substitution of one amino acid for another. Created by Ross Firestone.
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- If a point mutation changes 1 DNA codon, which changes 1 RNA codon, which changes 1 amino acid of the resulting protein, how is this different from a missense mutation, which is any mutation that changes one amino acid to another?(8 votes)
- The difference relies in the categorization of the mutation. If the mutation results in a change of one aminoacid, it is a missense mutation, no matter if it was result of a frameshift or point mutation. If the mutation is caused by the exchange of one base pair, it is a point mutation, no matter if it resulted in no change in the overall protein (silence mutation), in a change in one aminoacid (missense mutation) or in a stop codon (no-sense mutation). Hope this helps (although it was a little late).(9 votes)
- Someone help clarify. I got myself confused. My Kaplan book says a Nonsense mutation "occur when the change in nucleotide results in substituting a stop codon for an amino acid in the final protein". So a nonsense is when it leads to becoming a stop codon or substituting the stop codon?(2 votes)
- The Kaplan book is correct! In a nonsense mutation, a change in the genetic code leads to a STOP codon instead of an amino acid codon. Therefore the rest of the protein isn't formed because the translation process is halted early by the STOP codon. So, to answer your question, a nucleotide is SUBSTITUTED in the DNA causing an amino acid codon to BECOME a STOP codon in the translation process. Hope that clarifies!(8 votes)
- what's the difference between Missense mutation & Point mutation(0 votes)
- A missense mutation can be a point mutation. A point mutation is where you change one base in the DNA to another. A missense mutation occurs when that point mutation causes a different amino acid to be placed from that codon.
Because multiple codons code for the same amino acid, not all point mutations will cause a missense mutation.(9 votes)
- Would an addition/deletion of a multiple of three bases be considered a frameshift mutation?(3 votes)
- No, I am pretty sure the insertion or deletion of multiple of three base pairs is considered an in-frame mutation, which is different than a frameshift mutation.(0 votes)
- Can any one clarify the difference between point mutation and missense mutation? it looks similar. Thanks.(1 vote)
- A point mutation is going to change one nucleotide in the DNA code, this may or may not result in a changed amino acid. A missense mutation is always going to be a substitution of one amino acid for another.(4 votes)
- So the difference between missense mutation and point mutation is: When a single "base" is replaced on the DNA, it is simply called point mutation, whereas a replacement of "amino acid" in the protein is called missense mutation... We can also say, a missense mutation can occur BECAUSE of a point mutation. Hope this helps :)(2 votes)
- At around4:00you said that missense mutations can be divided into subgroups, one of them being silent mutations. If a missense mutation is swapping one AA out for another, how can it be that it is a silent mutation? Wouldn't it change the amino acid to another one, or do you mean the missense mutations only change an entire codon at once? Thanks!(1 vote)
- He had mistakenly said that missense mutation has subgroups..At3:46he corrected it with a subtext saying that its not :)(1 vote)
- can mutation be repaired?(1 vote)
- Yes. The first-line of defense is DNA polymerase which acts as a proofreading enzyme. Then different enzymes/proteins can preform mismatch repair on the mutated codon. There is also photoreactivation, which repairs thymine dimers but requires energy from light. Finally there is SOS repair when DNA has sustained heavy UV damage. This uses different DNA polymerase and lacks proofreading ability. The goal in SOS is not to repair but but allow to replication. Therefor, this SOS repair is only done when the mutations are dire and if not fixed the cell will die. Often this last ditch effort to replicate produces new mutations.(2 votes)
Voiceover: So, today 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. 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. So, what are the different types of mutations? Well, the first type of mutations we're going to talk about are called point mutations. Now, here I've just written 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. So, a point mutation is when one of our DNA bases is replaced with another. So, 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. Another type of mutation is called frame-shift, which works a little differently. So, first I'll write out the same DNA, RNA, and 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. 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. 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 of 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. 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 of these 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. 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. 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. 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 actually 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. So, in this example, CCA, CCG, CCT, and CCC in the section of DNA will all end up coding for glycine. So, if you change the third base, it 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, 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. 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. 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 results from a single glutamate residue being converted into a valine residue. 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. So, 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 on protein. In reference to DNA, we have point and frame-shift mutations, and in reference to protein, we have missense and non-sense mutations.