Pratique du Shadowing: The different types of mutations | Biomolecules | MCAT | Khan Academy - Apprendre l'anglais à l'oral avec YouTube
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Voiceover: So, today we're going to talk about the different types of genetic mutations that you would find in a cell.
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Voiceover: So, today we're going to talk about the different types of genetic mutations that you would find in a cell.
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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.
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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.
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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.
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So, we say that mutations are mistakes in a cell's DNA that ultimately lead to abnormal protein production.
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So, what are the different types of mutations?
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Well, the first type of mutations we're going to talk about are called point mutations.
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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.
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So, a point mutation is when one of our DNA bases is replaced with another.
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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.
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Another type of mutation is called frame-shift, which works a little differently.
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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.
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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.
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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.
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Now, instead of having three GAG codons, we've swapped out two for GGA codons.
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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.
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So, you can see that frame-shift mutations usually have more significant effects on the final protein than point mutations do.
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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.
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Now, our next type of mutations are non-sense mutations and missense mutations.
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Let's say we have a DNA sequence that normally generates RNA and codes for a cysteine amino acid.
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A non-sense mutation is any genetic mutation that leads to the RNA sequence becoming a stop codon instead.
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Now, missense mutations are a little different, and they're any genetic mutation that changes an amino acid from one to another.
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So, in this example, our mutation is changing the resulting amino acid from a cysteine to a tryptophan.
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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.
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So, now we can divide the missense mutations even further into a bunch of smaller categories.
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Silent mutations are when the mutation doesn't actually affect the protein at all.
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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.
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So, in this example, CCA, CCG, CCT, and CCC in the section of DNA will all end up coding for glycine.
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So, if you change the third base, it wouldn't affect the final protein.
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Conservative mutations are where the new amino acid is of the same type as the original.
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So, here I have a glutamate and an aspartate, which are both acidic amino acids.
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So, a mutation that swapped out an aspartate for a glutamate would be a conservative mutation.
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Finally, a nonconservative mutation is one with a new amino acid is of a different type from the original.
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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.
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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.
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So, let's look at a quick example.
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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.
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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.
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So, what did we learn?
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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.
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In reference to DNA, we have point and frame-shift mutations, and in reference to protein, we have missense and non-sense mutations.
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Context & Background
In this educational video, the speaker delves into the complex topic of genetic mutations, presenting them within the framework of molecular biology. By beginning with the central dogma, which outlines how DNA is transcribed into RNA and subsequently translated into proteins, the speaker sets a solid foundation for understanding mutations. The discussion covers various types of mutations, such as point mutations, frame-shift mutations, and their impacts on protein production. This content is not only informative for aspiring scientists but is also a valuable resource for English learners looking to enhance their technical vocabulary and comprehension in a scientific context.
Top 5 Phrases for Daily Communication
- “Genetic mutations are mistakes in a cell's DNA.” - This phrase is fundamental for discussing genetics.
- “Point mutation affects one DNA base.” - A concise definition valuable for any biology conversation.
- “Frame-shift mutations change the reading frame of RNA.” - This phrase helps in explaining complex mutations clearly.
- “Nonsense mutations lead to stop codons.” - Critical for talking about the effects of mutations on proteins.
- “Missense mutations change one amino acid to another.” - Useful for describing how mutations can alter proteins.
Step-by-step Shadowing Guide
To effectively utilize the shadowing technique while practicing the content from this video, follow these steps:
- Listen Actively: Start by watching the video once without any pauses. Focus on the speaker's pronunciation and intonation.
- Segment the Content: Divide the video into segments that correspond to the key points made. Each segment can be practiced individually for better retention.
- Rewind and Repeat: Use a shadowing app to slow down the video if necessary. Listen to a sentence or phrase, pause, and then repeat it aloud, mimicking the speaker's tone and pace. This process is known as shadow speech.
- Record Yourself: After you feel comfortable with a segment, record yourself speaking the same lines. This will help you identify areas for improvement in your pronunciation and fluency.
- Practice Consistently: Set aside time each day for your english speaking practice. Consistency is key, and using the shadowspeak technique will enhance your learning experience.
By incorporating these steps into your practice routine, you will develop a deeper understanding of both the scientific concepts and the English language, making your learning journey both comprehensive and engaging.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.
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