シャドーイング練習: PCR (Polymerase Chain Reaction) - 動画で英語スピーキングを学ぶ

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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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このレッスンの語彙とスピーキングのポイント

繰り返し出てくる語は次のとおりです：Dna, Pcr, polymerase, step, copies。この動画には、シャドーイング用の文が83文、単語が1299語あります。音声の長さは7:30です。話す速さは1分あたり約173語で、日常会話に近い自然なペースです。英語の頻出3,000語に含まれる単語は81%だけなので、語彙は難しめです。

この動画の重要語彙

動画に出てくる覚えておきたい単語15語を、発音と意味つきで紹介します。

単語	発音	意味
virus 名詞	/ˈvaɪ.ɹəs/	ウイルス, ウィルス
enzyme 名詞	/ˈɛn.zaɪm/	酵素
molecule 名詞	/ˈmɑ.lɪ.kjul/	分子
synthesis 名詞	/ˈsɪnθəsɪs/	統合, 総合
genetic 形容詞	/d͡ʒəˈnɛt.ɪk/	遺伝的
identification 名詞	/aɪˌdɛn(t)ɪfɪˈkeɪʃn̩/	識別
jam 名詞	/ˈd͡ʒæm/	ジャム
curious 形容詞	/ˈkjʊɹ.i.əs/	好奇心の強い, 知りたがる
ideal 形容詞	/aɪˈdi(ə)l/	理想的な, 理想な
recall 動詞	/ɹɪˈkɔl/	呼び返す
remind 動詞	/ɹəˈmaɪnd/	思い出させる
tube 名詞	/tuːb/	チューブ
sequence 名詞	/ˈsiː.kwəns/	順序
throat 名詞	/ˈθɹoʊt/	喉
segment 名詞	/ˈsɛɡmɛnt/	切片

繰り返し練習したい文

動画に出てくる短く完結した文です。日常会話でそのまま使えます。

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

この動画の文法

話し手がよく使っている文型を、動画の実際の表現とともに紹介します。

文型	動画での表現
受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる	have been separated · is automated · can be performed
現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している	you've jammed · I've developed · You've heard

注意したい発音

話し手はwe'll, we're, we'veなど、短縮形や弱形を16回使っています。聞こえたとおりの短い形で発音しましょう。

「th」の音: synthesis /ˈsɪnθəsɪs/, throat /ˈθɹoʊt/
「sh」と「zh」の音: identification /aɪˌdɛn(t)ɪfɪˈkeɪʃn̩/, appreciation /əˌpɹiː.ʃiˈeɪ.ʃən/, transcription /tɹænˈskɹɪpʃən/, suggestion /səˈd͡ʒɛst.ʃən/, instruction /ɪnˈstɹʌkʃən/
長い単語（アクセントの位置に注意）: identification /aɪˌdɛn(t)ɪfɪˈkeɪʃn̩/, appreciation /əˌpɹiː.ʃiˈeɪ.ʃən/, biology /baɪˈɑ.lə.d͡ʒi/, complexity /kəmˈplɛk.sɪ.ti/, limitation /lɪmɪˈteɪʃən/

日本語話者が苦手な音：

/r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: viral /ˈvaɪɹəl/, recall /ɹɪˈkɔl/, briefly /ˈbɹiːfli/, illustrate /ˈɪl.əˌstɹeɪt/, complementary /ˌkɑmplɪˈmɛnt(ə)ɹi/
/v/ — /b/ にならないように、上の歯を下唇に当てる: virus /ˈvaɪ.ɹəs/, reverse /ɹɪˈvɝs/, viral /ˈvaɪɹəl/, convert /kənˈvɝt/, involve /ɪnˈvɑlv/
/f/ — 「フ」ではなく、上の歯と下唇で出す: fancy /ˈfæn.si/, identification /aɪˌdɛn(t)ɪfɪˈkeɪʃn̩/, briefly /ˈbɹiːfli/, fixing /ˈfɪksɪŋ/, buffer /ˈbʌfəɹ/

この動画での練習方法

まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
自分の声を録音して元の音声と比べます。virus, enzyme, moleculeなどの単語に特に注意しましょう。

シャドーイングとは？英語上達に効果的な理由

シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。

シャドーイングのやり方: ステップ別の完全ガイドを読む →

シャドーイング練習: PCR (Polymerase Chain Reaction) - 動画で英語スピーキングを学ぶ

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