跟读练习: Glycolysis - 通过视频学习英语口语

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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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本课的词汇与口语要点

视频中反复出现的词有：glucose, glycolysis, enzyme, pathway, fructose。这段视频共有 170 个句子、2233 个单词可供跟读。讲话部分时长为 14:16。说话人语速自然，每分钟约 156 个词，接近日常对话。只有 76% 的单词属于英语最常用的 3,000 词，词汇难度较高。

视频中的重点词汇

视频中 15 个值得学习的单词，附发音和释义：

单词	发音	释义
enzyme 名词	/ˈɛn.zaɪm/	酶, 酵素
mechanism 名词	/ˈmɛk.ə.nɪ.zəm/	機械 /机械, 機構 /机构
affinity 名词	/əˈfɪnɪti/	親和力 /亲和力
slide 名词	/ˈslaɪ̯d/	滑梯
yield 动词	/jiːld/	產量 /产量, 產生 /产生
insulin 名词	/ˈɪnsəlɪn/	胰島素 /胰岛素
occur 动词	/əˈkɜː/	發生 /发生
concentration 名词	/ˌkɑn.sənˈtɹeɪ.ʃən/	專注力 /专注力
beta 名词	/ˈbeɪtə/	貝塔 /贝塔
acid 名词	/ˈæsɪd/	酸
refer 动词	/ɹɪˈfɜː/	談到 /谈到
tissue 名词	/ˈtɪʃ.(j)u/	纸巾
overview 名词	/ˈoʊ.vɚˌvjuː/	概觀 /概观
equation 名词	/ɪˈkweɪ.ʒən/	方程式, 方程
sensor 名词	/ˈsɛn.sɚ/	傳感器 /传感器

视频中出现的短语动词

单词	释义
break down 动词	壞了 /坏了, 出故障

值得反复跟读的句子

视频中简短而完整的句子，可以直接用在日常对话里：

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.

视频中的语法

说话人最常用的结构，并附上视频中的原话：

结构	视频中的用法
被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的	is brought · is composed · is only found
现在完成时 have/has + 过去分词 — 过去发生但与现在仍有关联的事	I've created · we've understood · I've put
定语从句 who / which + 从句 — 补充说明人或事物	phosphoenolpyruvate which will · AMP, which is · pyruvate, which can

需要注意的发音

说话人用了 41 次缩略和弱读形式，例如 don't, you're, we're。请按听到的简短形式来说。

“sh” 和 “zh” 音: concentration /ˌkɑn.sənˈtɹeɪ.ʃən/, tissue /ˈtɪʃ.(j)u/, conversion /kənˈvɝʒən/, equation /ɪˈkweɪ.ʒən/, donation /doʊˈneɪʃən/
长单词——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/

中文母语者容易读错的音：

/v/ — 不要读成 /w/，上齿轻触下唇: convert /kənˈvɝt/, conversion /kənˈvɝʒən/, overview /ˈoʊ.vɚˌvjuː/, reverse /ɹɪˈvɝs/, intuitive /ɪnˈtjuːɪtɪv/
词尾辅音 — 要读清楚，后面不要加元音: glucose /ˈɡluː.kəʊz/, convert /kənˈvɝt/, slide /ˈslaɪ̯d/, yield /jiːld/, acid /ˈæsɪd/
/r/ 和 /l/ 的区别: regulatory /ˈɹɛɡ.jʊ.lə.t(ɔː.)ɹi/, irreversible /ˌɪr.ɪˈvɝ.sə.bəl/, preferentially /ˈpɹɛf.ɜː(ɹ)ˌɛn.ʃə.li/, reciprocal /ɹɪˈsɪpɹək(ə)l/

如何用这段视频练习

先完整听一遍视频，不要开口，记下不认识的单词。
先用 0.75 倍速逐句跟读，熟练之后再回到正常速度。
录下自己的声音并与原声对比，特别注意 enzyme, mechanism, affinity 这类单词。

什么是跟读法？

跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。

影子跟读法: 阅读完整分步指南 →

跟读练习: Glycolysis - 通过视频学习英语口语

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