跟讀練習: Glycolysis - 通過影片學習英語口語

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Welcome back to the high -yield biochemistry series.

This is brought to you by Dirty Medicine.

In today's video, we're going to continue our discussion about the biochemical pathways and talk about glycolysis.

Glycolysis is typically the first biochemical pathway that you learn when you're learning about biochemistry, and it's because of that that it's extremely high -yield.

It shows up on exams all of the time.

Now, when you're learning about glycolysis, as you'll see me mention throughout this video, it's really important to remember the bigger picture.

And when I say that, I'm referring to things like what is the function or the role of glycolysis?

What are we taking as a reactant and turning into a product?

And what are the regulatory mechanisms in terms of feedback?

So what makes this go forward?

What inhibits this?

And what is the rate limiting enzyme?

Just like all of the biochemistry videos that I've created, you need to know the rate -limiting enzyme and the regulatory mechanisms.

So we're talking about things like inhibitors, etc. So let's start with a quick overview of glycolysis.

Glycolysis is an irreversible biochemical reaction that occurs in the cytoplasm.

The net equation for glycolysis is that you start with glucose, and the goal is to take that glucose and turn it into pyruvate,

where it can downstream take multiple pathways through that pyruvate pathway

and preferentially usually this goes into the citric acid cycle

but here's the net equation you've you start with glucose

and you add two phosphates two adps and two nads

and what you get out of

that is two 2 pyruvates plus 2 ATPs plus 2 NADH plus 2 hydrogens plus 2 waters.

But if you wanted to just think very simply about what glycolysis is doing,

it's taking glucose and breaking that glucose down into storable products that the body can use in other biochemical pathways.

So now that we've understood the overview of glycolysis, let's just get into the meat and potatoes here.

We're going to talk about the pathway.

You need to understand the pathway, and I'm going to pay very special attention to the regulatory mechanisms of this pathway and the rate -limiting enzyme.

So you start with glucose, right?

Any person takes a bite of a cheeseburger, eats a french fry, drinks a milkshake, and they've got a bunch of carbohydrate in their body.

And that carbohydrate is composed usually of glucose.

And if it's not of glucose, then the other types of sugars will get turned into glucose so

that glycolysis can utilize

it the first step is glucose will get turned into glucose

6 -phosphate glucose 6 -phosphate will get turned into fructose

6 -phosphate fructose 6 -phosphate will get turned into fructose 1 -6 -bisphosphate

and now you've got like multiple steps

that are going to happen there's going to be four

or five more reactions in this pathway and you'll end up with phosphoenolpyruvate which will get turned into pyruvate.

And going from glucose down to pyruvate is the entire glycolysis pathway.

So when you get to pyruvate you're basically finished with glycolysis.

Now let's talk about the important enzymes that you need to know.

So the first step that converts glucose to glucose 6 -phosphate, there's actually two different enzymes

that can be used depending on the circumstances of the glucose concentration and where in the body we're talking about.

So those two enzymes are glucokinase and hexokinase.

So to be perfectly clear, either glucokinase or hexokinase can convert glucose to glucose 6 -phosphate.

And what you'll need to know for test day that's really high yield is to understand under

which circumstances both of these enzymes might be used.

So for glucokinase, this enzyme has a low affinity and a high

Km, Just remember the reciprocal relationship between affinity and Km.

The higher the Km, the lower the enzyme has an affinity for its substrate.

So glucokinase has a low affinity for glucose.

It typically doesn't want to go and grab glucose.

And the reason for this is because glucokinase acts as a glucose sensor.

It's present in the liver and the pancreatic beta cells, and it's only used when glucose is at high concentrations.

So basically what you should think of glucokinase as is an emergency enzyme that is acting as a glucose sensor.

And it's really not grabbing glucose because instead of grabbing glucose and breaking it down through glycolysis,

what it's doing is it's sensing glucose and it's going, okay, let's test how much glucose is over here.

uh that's okay we're not going to jump in yet um hexokinase you go first

so hexokinase on the other hand that is a high affinity enzyme

which means it has a low km and

because it has high affinity for its substrate hexokinase is the one that's constantly going to be latching onto glucose

and converting it to glucose 6 -phosphate and sending it down the glycolysis pathway

and the reason for that is because hexokinase is the enzyme that's used to operate the basal glucose metabolism.

So constantly throughout your body in all of your tissues, you have this enzyme hexokinase that's just keeping a basal level of glucose metabolism present.

It's trying to make sure that your glucose level is adequate throughout the body in all of the tissues.

But if hexokinase becomes overwhelmed because suddenly there's a massive influx of glucose, that is when hexokinase turns to glucokinase and says,

glucose, I know you usually have a low affinity, but I really need some help now because the glucose concentration is high.

So if you think about it, that's the reason that glucokinase is only found in the liver and the pancreatic beta cells,

because it does a very specific regulatory job where it's only acting when the blood glucose levels are super, super high.

When that concentration reaches some critical point, that's when glucokinase in the liver and the pancreatic beta cells jumps in to save hexokinase.

So the takeaway from this slide is that both glucokinase

and hexokinase are enzymes that catalyze that conversion from glucose to glucose 6 -phosphate.

The only difference is that hexokinase is kind of there all of the time, making a basal level of glucose, and glucokinase jumps in in emergencies.

But understand the differences between those two enzymes that I've put in the gray boxes.

They are extremely high yield and probably will show up on your test.

So here's where we are.

We've talked about the enzymes in the first step.

The enzyme that converts fructose 6 -phosphate to fructose 1 ,6 -bisphosphate is the rate -limiting enzyme of glycolysis,

and that's phosphofructokinase 1.

Sometimes you'll hear this referred to as PFK1.

So PFK1, or phosphofructokinase 1, is the rate -limiting enzyme, and it converts fructose 6 -phosphate to fructose 1 ,6 -bisphosphate.

Now, I told you at the start of this video

that the very important thing to keep in mind for USMLE and Comlex is the regulatory mechanisms.

And what I mean when I say regulatory mechanisms are what inhibits this pathway and what promotes this pathway.

And we're going to talk about that for the first time right here.

And because phosphofructokinase 1 is the rate -limiting enzyme,

it's really high yield to understand what inhibits phosphofructokinase 1 and what promotes phosphofructokinase 1.

And that's what you see here.

So ATP and citrate will inhibit the rate -limiting enzyme PFK1,

but AMP will promote the rate -limiting enzyme of PFK1.

And this should be somewhat intuitive to you.

So think about what glycolysis is doing.

The role of glycolysis is to take glucose, convert it to pyruvate and ATP,

and then let that pyruvate enter one of many different pathways, but usually the citric acid cycle where you'll then create citrate.

So if you think about that,

the question becomes, what would this pathway want to do if it already had ATP and therefore didn't need to make it,

or if it already had citrate and therefore didn't need to make pyruvate, which would then go to citrate.

And that's why ATP and citrate inhibit PFK1, because if you have ATP and you already have citrate, then you don't need to do glycolysis.

So the presence of those products will inhibit the rate -limiting enzyme, and therefore glycolysis won't occur.

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Now, likewise, think about AMP.

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If you have AMP, which is monophosphate, only one, you don't have ATP.

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And therefore, if you don't have ATP, you want to do glycolysis.

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So in the presence of AMP, which is to say in a situation where you don't have ATP,

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AMP will promote PFK1 and will therefore promote glycolysis.

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So anytime you're not really sure about how the regulatory mechanisms are working, think about this intuitively.

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Ask yourself on test say, well, would glycolysis happen if there was AMP?

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Would glycolysis happen if there was citrate?

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It should make sense to you if you understand what the big picture role of these pathways are.

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So that's what promotes and inhibits PFK1.

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Now I need to pause for a second and tell you about this little nuance of glycolysis.

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So fructose 6 -phosphate can go to fructose 1 ,6 -bisphosphate as you see on this slide.

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But additionally, there's sort of a side step that occurs, a pivot if you will.

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Fructose 6 -phosphate can also become fructose 2 ,6 -bisphosphate.

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And if fructose 6 -phosphate will become fructose 2 ,6 -bisphosphate,

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the enzyme that catalyzes this conversion is phosphofructokinase 2, PFK2.

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So very similarly named, of course, to the rate limiting enzyme that we just talked about, but instead of 1, it's 2.

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So when this happens, you create fructose 2 ,6 -bisphosphate.

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And interestingly, that fructose 2 ,6 -bisphosphate will promote PFK1.

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So the goal when the body does this is to make glycolysis happen faster.

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Now the question then becomes what is promoting or inhibiting phosphofructokinase 2 or PFK2?

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And that's really simple.

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So it's going to be inhibited by glucagon and it's going to be promoted by insulin.

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So think about it.

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If fructose 2 ,6 -bisphosphate makes glycolysis happen faster.

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And in glycolysis, you're breaking down glucose.

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It makes sense that insulin will promote PFK2 because in the presence of glucose,

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the body's going to secrete insulin and the body's telling anything that any cell that has a glycolysis pathway occurring, it's like, yo, take that glucose,

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break it down, please get this out of the system.

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And that's insulin's role.

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The opposite of that is glucagon.

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Glucagon's putting the brakes on this pathway and saying, yo, chill, we need to reverse this and make energy available because blood glucose is low.

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So think about it, guys.

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Insulin will promote PFK2 because it will make fructose 2 ,6 -bisphosphate, which feeds back to PFK1 and makes this happen faster.

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But in another situation, glucagon will inhibit PFK2 because PFK2 would normally make fructose 2 ,6 -bisphosphate,

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which would feed back to PFK1 and make this process happen faster.

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So again, understanding the big picture about what glycolysis is actually doing helps you understand the regulatory mechanisms

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that you need to memorize for your test.

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So the takeaway from this slide is that PFK2 inhibited by glucagon and promoted by insulin.

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The last enzyme that we need to talk about is the enzyme that converts phosphoenolpyruvate to pyruvate, the last step of glycolysis.

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That enzyme is pyruvate kinase.

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And just like PFK1, this is going to be inhibited by ATP and citrate for the same exact reasons.

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And those reasons are, again, glycolysis wants to create ATP.

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Glycolysis wants to make pyruvate, which can then become citrate in the TCA cycle.

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So therefore, if you already have ATP or you already have citrate, what's the point?

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You don't need to do glycolysis.

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So the presence of those products will inhibit the enzymes that usually make glycolysis work.

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So guys, that's it for glycolysis.

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And you're probably sitting there starting to have a panic attack thinking about, whoa, dirty.

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What about all the other enzymes?

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Don't worry about the other enzymes.

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This is what you need to know for USMLE and Comlex.

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You need to know the enzymes I put in these slides, the regulatory mechanisms that I put in these slides,

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and understand the difference between glucokinase and hexokinase that we discussed at the beginning of this video.

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All of the other intermediary steps, you don't need to know them.

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You really don't.

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They're not going to show up on your test unless you're taking a college level or intro to biochemistry course.

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You really don't need to know them.

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If you do want to know them for completeness sake, I would encourage you to go online, look at some diagrams, memorize some enzymes.

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But this is what you need to know to answer 99 % of the questions that will show up on USMLE,

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Comlex, your question banks, your practice tests, et cetera.

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So again, and I cannot stress this enough because it's the biggest theme for all of biochemistry.

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Know the rate limiting enzyme, know the regulatory mechanisms.

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And if you get stuck on test day about what's inhibiting or what's promoting, ask yourself, what's the goal of this pathway?

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And therefore, what do I think might happen?

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That's it.

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If you liked this video, drop me a like or a comment in the comment section.

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Please remember to check my Patreon page.

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You can click

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that link in the description of any of my videos sign up to send a secure monthly donation

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and support the channel love you good luck

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本課的詞彙與口語要點

影片中反覆出現的詞有：glucose, glycolysis, enzyme, pathway, fructose。這段影片共有 170 個句子、2233 個單詞可供跟讀。講話部分時長為 14:16。說話人語速自然，每分鐘約 156 個詞，接近日常對話。只有 76% 的單詞屬於英語最常用的 3,000 詞，詞彙難度較高。

影片中的重點詞彙

影片中 15 個值得學習的單詞，附發音和釋義：

單詞	發音	釋義
enzyme 名詞	/ˈɛn.zaɪm/	酶, 酵素
mechanism 名詞	/ˈmɛk.ə.nɪ.zəm/	機械 /機械, 機構 /機構
affinity 名詞	/əˈfɪnɪti/	親和力 /親和力
slide 名詞	/ˈslaɪ̯d/	滑梯
yield 動詞	/jiːld/	產量 /產量, 產生 /產生
insulin 名詞	/ˈɪnsəlɪn/	胰島素 /胰島素
occur 動詞	/əˈkɜː/	發生 /發生
concentration 名詞	/ˌkɑn.sənˈtɹeɪ.ʃən/	專注力 /專注力
beta 名詞	/ˈbeɪtə/	貝塔 /貝塔
acid 名詞	/ˈæsɪd/	酸
refer 動詞	/ɹɪˈfɜː/	談到 /談到
tissue 名詞	/ˈtɪʃ.(j)u/	紙巾
overview 名詞	/ˈoʊ.vɚˌvjuː/	概觀 /概觀
equation 名詞	/ɪˈkweɪ.ʒən/	方程式, 方程
sensor 名詞	/ˈsɛn.sɚ/	感測器 /感測器

影片中出現的短語動詞

單詞	釋義
break down 動詞	壞了 /壞了, 出故障

值得反覆跟讀的句子

影片中簡短而完整的句子，可以直接用在日常對話裡：

What are we taking as a reactant and turning into a product?
We're going to talk about the pathway.
We've talked about the enzymes in the first step.
You don't need to do glycolysis.
You really don't need to know them.

影片中的語法

說話人最常用的結構，並附上影片中的原話：

結構	影片中的用法
被動語態 be + 過去分詞 — 強調發生了什麼，而不是誰做的	is brought · is composed · is only found
現在完成時 have/has + 過去分詞 — 過去發生但與現在仍有關聯的事	I've created · we've understood · I've put
定語從句 who / which + 從句 — 補充說明人或事物	phosphoenolpyruvate which will · AMP, which is · pyruvate, which can

需要注意的發音

說話人用了 41 次縮略和弱讀形式，例如 don't, you're, we're。請按聽到的簡短形式來說。

“sh” 和 “zh” 音: concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, tissue /ˈtɪʃ.(j)u/, conversion /kənˈvɝʒən/, equation /ɪˈkweɪ.ʒən/, donation /doʊˈneɪʃən/
長單詞——注意重音位置: regulatory /ˈɹɛɡ.jʊ.lə.t(ɔː.)ɹi/, mechanism /ˈmɛk.ə.nɪ.zəm/, affinity /əˈfɪnɪti/, concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, metabolism /məˈtæb.əˌlɪz.əm/

中文母語者容易讀錯的音：

/v/ — 不要讀成 /w/，上齒輕觸下唇: convert /kənˈvɝt/, conversion /kənˈvɝʒən/, overview /ˈoʊ.vɚˌvjuː/, reverse /ɹɪˈvɝs/, intuitive /ɪnˈtjuːɪtɪv/
詞尾子音 — 要讀清楚，後面不要加母音: glucose /ˈɡluː.kəʊz/, convert /kənˈvɝt/, slide /ˈslaɪ̯d/, yield /jiːld/, acid /ˈæsɪd/
/r/ 和 /l/ 的區別: regulatory /ˈɹɛɡ.jʊ.lə.t(ɔː.)ɹi/, irreversible /ˌɪr.ɪˈvɝ.sə.bəl/, preferentially /ˈpɹɛf.ɜː(ɹ)ˌɛn.ʃə.li/, reciprocal /ɹɪˈsɪpɹək(ə)l/

如何用這段影片練習

先完整聽一遍影片，不要開口，記下不認識的單詞。
先用 0.75 倍速逐句跟讀，熟練之後再回到正常速度。
錄下自己的聲音並與原聲對比，特別注意 enzyme, mechanism, affinity 這類單詞。

什麼是跟讀法？

跟讀法 (Shadowing) 是一種有科學依據的語言學習技巧，最初開發用於專業口譯員的培訓，並由多語言者Alexander Arguelles博士普及。這個方法簡單而強大：您在聽英語母語原聲的同時立即大聲重複——就像是一個延遲1-2秒緊跟說話者的影子。與被動聽力或語法練習不同，跟讀法強迫您的大腦和口腔肌肉同時處理並模模擬實的講話模式。研究表明它能顯著提高發音準確性，語調，節奏，連讀，聽力理解和口語流利度——使其成為雅思口語備考和真實英語交流最有效的方法之一。

影子跟讀法: 閱讀完整分步指南 →

跟讀練習: Glycolysis - 通過影片學習英語口語

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