Практика Shadowing: PCR (Polymerase Chain Reaction) - Изучайте разговорный английский по видео

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There are some pieces of technology you really develop an appreciation for.

Maybe it's your phone, your laptop, your drawing tablet, but for me, it is the copy machine.

Oh, the copy machine.

I know it's not possible, but I could promise you that whenever the copy machine was aware of my presence, that's when it decided to malfunction,

especially if it knew I was short on time.

And of course, when it jams, the fancy copy machines will even tell you what is wrong and how to fix it,

but my experience with trying to follow the instructions of fixing the copy machine makes it worse, and then by that point there's a line,

and you feel your heart pounding, and you're embarrassed because now you've jammed it for everyone.

Yeah, so while I've developed an appreciation and respect for the copy machine, I've definitely tried to limit my use of it over the years.

Saves paper anyway.

You may be wondering why is she spending so much time on this?

Well I want to call your attention to a technology, a biotechnology, that works almost like an amazing and fancy copy machine.

Except not for something on paper.

No, it's for DNA.

This biotechnology is PCR.

Polymerase Chain Reaction, or PCR for short.

It provides a way to make more copies of a portion of DNA.

Lots and lots and lots of DNA copies, and this technology does NOT need to happen in a cell either.

In fact, it can happen in a test tube.

And so you may wonder, number one, how does PCR work?

And number two, why?

Why make more copies of some specific portion of DNA?

So let's briefly answer those two questions.

To answer the first question, the how does this work question,

let's talk about what we need first before we get to the steps of how it works.

We need the DNA portion that we want to make copies of, we need some kind of buffer to put it in,

and then we need things that would be necessary to make more copies of the DNA.

So think about what that might mean from our DNA replication video.

We'll need primers.

Recall that primers help DNA polymerase, a building enzyme, know where to go to start its building.

We need DNA polymerase, the building enzyme.

Fun fact, the DNA polymerase used is often a heat -resistant type of DNA polymerase as PCR uses heat.

Typically, the polymerase chosen for the job is tach polymerase, a type of of heat -resistant DNA polymerase.

Tac polymerase is originally from a type of bacteria that can handle and live in really high temperatures in nature, in hot springs.

Pretty cool.

We also need DNA nucleotides for the DNA polymerase to build with.

So we can look at the PCR sequence in three major steps.

We'll illustrate with one double -stranded DNA molecule here, and let's assume this is what we want replicated.

Step 1.

Denaturation.

You've heard that word denature before, right, when we were talking about enzymes?

One way we had talked about denaturing enzymes was using heat.

And heat is what we will use in this step.

This step involves the addition of heat needed to separate the two strands of the DNA molecule.

Step 2.

Annealing.

This word means something a little different in biology.

Basically this is when the two DNA strands

that now have been separated by that heat are going to be cooled and be joined by the primers.

The temperature for this step should allow the primers to bind to the specific segment of DNA that you want to amplify,

which means make copies of.

Step 3.

DNA synthesis.

Remember, synthesis means to make something.

With DNA synthesis, we're going to make more copies of DNA, and to do so, DNA polymerase will begin to work on both of these strands

and it will use the DNA nucleotides as its building material to amplify the DNA.

We should note that the temperature at this step may be a little warmer than the previous step.

It needs to be a temperature that is ideal for the specific DNA polymerase used.

Now after finishing one cycle of this, you have two double -stranded DNA molecules, right?

Similar to how it would be in DNA replication within a cell.

But you can repeat this now, except this time you now have two double -stranded DNA molecules to start with.

So you repeat with the denaturation, annealing, and DNA synthesis steps, now you have four double -stranded DNA molecules.

You repeat the steps again, now you have eight.

And if the process is automated by a machine, which, why yes, they do have in science catalogs, you can actually do this fairly quickly.

Which brings you to, why?

Why do this?

Well, any technology that needs copies of a portion of DNA could find PCR useful, but But we'll just mention two examples in our limited time.

We mentioned DNA fingerprinting in our gel electrophoresis video, and we mentioned that DNA fingerprinting can be part of a crime scene investigation.

Well, in order to have enough copies of DNA samples to run in gel electrophoresis to analyze,

PCR can be performed to make copies of the of the fragments of DNA that are found at a crime scene.

Another example?

Diagnosis of a disease, such as one caused by a virus.

For an especially relevant example, I can mention one of the testing types done for the virus that causes COVID -19.

COVID -19 is a pandemic that we're experiencing right now in 2020.

And the virus that causes COVID -19 is called SARS -CoV -2.

You might have heard of one test type that uses a sample from a nose or throat swab in a PCR test,

but to be more specific, this test for this virus is a real -time reverse transcription PCR test.

The reason it has this fancier reverse transcription in there is

because this virus uses RNA as its genetic material instead of DNA,

and you have to use an enzyme called reverse transcriptase to convert the RNA into DNA.

So before we can do the regular PCR steps we've mentioned, we must convert isolated and purified RNA into DNA.

A specific primer is added that will bind to an area of viral RNA,

and then reverse transcriptase is used to convert viral RNA into cDNA .

Using specific primers and the TAC DNA polymerase,

the cDNA can be copied over and over each cycle in the familiar steps we've been mentioning of PCR.

See the goal is you need enough copies of the viral cDNA in order for it to be detectable.

The idea being if it's a positive result, you have the selective primers binding and you have the TAC DNA polymerase making more

and more copies of the viral cDNA each cycle.

In addition, specific fluorescent probes are also used for identification.

A certain level is needed for identification of a positive result.

And if the virus's genetic material is not present in the sample, then primers wouldn't bind, and there would be no cDNA copies produced.

If you'd like to learn more about this test as far as its limitations

and also its complexity as we're being pretty general here, we've included some further reading suggestions in the video details.

So those were just two examples of how PCR can be used,

but there are many more examples in our suggested further reading links in the video description.

Overall, PCR is such a useful and fascinating technology that will likely remain indispensable for future uses.

It's a rare day when I pull out that word, indispensable.

Well, that's it for the Amoeba Sisters, and we remind you to stay curious.

I'll see you next time.

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Лексика и советы по произношению к этому уроку

Чаще всего повторяются слова: Dna, Pcr, polymerase, step, copies. В этом видео 83 предложений и 1299 слов для шедоуинга. Речь длится 7:30. Говорящий говорит в естественном темпе, около 173 слов в минуту, близком к повседневной речи. Только 81% слов входят в 3000 самых частых слов английского языка, поэтому лексика сложная.

Ключевая лексика этого видео

15 слов из видео, которые стоит выучить, с произношением и значением:

Слово	Произношение	Значение
strand существительное	/ˈstɹænd/	жи́ла, нить
virus существительное	/ˈvaɪ.ɹəs/	ви́рус
enzyme существительное	/ˈɛn.zaɪm/	ферме́нт, энзи́м
molecule существительное	/ˈmɑ.lɪ.kjul/	моле́кула
viral прилагательное	/ˈvaɪɹəl/	ви́русный
synthesis существительное	/ˈsɪnθəsɪs/	си́нтез
fancy существительное	/ˈfæn.si/	воображе́ние, фанта́зия
convert глагол	/kənˈvɝt/	превраща́ть, преврати́ть
genetic прилагательное	/d͡ʒəˈnɛt.ɪk/	генети́ческий
identification существительное	/aɪˌdɛn(t)ɪfɪˈkeɪʃn̩/	идентифика́ция, опознава́ние
jam существительное	/ˈd͡ʒæm/	джем, варе́нье
appreciation существительное	/əˌpɹiː.ʃiˈeɪ.ʃən/	благода́рность, призна́тельность
curious прилагательное	/ˈkjʊɹ.i.əs/	любопы́тный, любозна́тельный
ideal прилагательное	/aɪˈdi(ə)l/	идеа́льный
recall глагол	/ɹɪˈkɔl/	отзыва́ть, отозва́ть

Фразовые глаголы, которые вы услышите

Слово	Значение
pull out глагол	выходи́ть, вы́йти

Фразы, которые стоит повторять

Короткие законченные фразы из видео, которые пригодятся в повседневном разговоре:

You’ve heard that word “denature” before, right?
When we were talking about enzymes?
Which brings you to…why?

Грамматика в этом видео

Конструкции, которые говорящий использует чаще всего, с точными словами из видео:

Конструкция	В видео
Пассивный залог be + причастие прошедшего времени — важно, что происходит, а не кто это делает	have been separated · is automated · can be performed
Present Perfect have/has + причастие прошедшего времени — прошлое действие, важное сейчас	you've jammed · I've developed · You've heard

Произношение, на которое стоит обратить внимание

Говорящий использует 16 сокращённых и редуцированных форм, например we'll, we're, we've. Произносите их коротко, так, как слышите.

Звуки «th»: synthesis /ˈsɪnθəsɪs/, throat /ˈθɹoʊt/
Звуки «sh» и «zh»: identification /aɪˌdɛn(t)ɪfɪˈkeɪʃn̩/, appreciation /əˌpɹiː.ʃiˈeɪ.ʃən/, transcription /tɹænˈskɹɪpʃən/, suggestion /səˈd͡ʒɛst.ʃən/, instruction /ɪnˈstɹʌkʃən/
Длинные слова — следите за ударением: identification /aɪˌdɛn(t)ɪfɪˈkeɪʃn̩/, appreciation /əˌpɹiː.ʃiˈeɪ.ʃən/, biology /baɪˈɑ.lə.d͡ʒi/, complexity /kəmˈplɛk.sɪ.ti/, limitation /lɪmɪˈteɪʃən/

Звуки, трудные для русскоязычных:

/w/ — губы округлены, это не /v/: sequence /ˈsiː.kwəns/, swab /swɒb/
Звонкие согласные в конце слова — не оглушайте их: strand /ˈstɹænd/, bind /ˈbaɪ̯nd/, remind /ɹəˈmaɪnd/, tube /tuːb/, pound /ˈpaʊ̯nd/

Как заниматься с этим видео

Прослушайте всё видео один раз молча и выпишите незнакомые слова.
Начните со скорости 0,75×, повторяйте предложение за предложением и вернитесь к обычной скорости, когда станет легко.
Запишите себя и сравните с оригиналом, обращая внимание на такие слова, как strand, virus, enzyme.

Что такое техника Shadowing?

Shadowing — это научно обоснованная техника изучения языка, изначально разработанная для подготовки профессиональных переводчиков и популяризированная полиглотом доктором Александром Аргуэльесом. Метод прост, но эффективен: вы слушаете аудио на английском от носителей языка и немедленно повторяете вслух — как тень, следующая за говорящим с задержкой в 1–2 секунды. В отличие от пассивного прослушивания или грамматических упражнений, Shadowing заставляет мозг и мышцы рта одновременно обрабатывать и воспроизводить реальные речевые паттерны. Исследования показывают, что это значительно улучшает точность произношения, интонацию, ритм, связную речь, понимание на слух и беглость речи — что делает его одним из самых эффективных методов для подготовки к IELTS Speaking и реального общения на английском.

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Практика Shadowing: PCR (Polymerase Chain Reaction) - Изучайте разговорный английский по видео

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