邊學英語邊複習生理學(2) | 8分鐘了解簡單擴散

In this segment on cell membrane transport, we’re now going to be focusing on the various types of membrane transport. Now specifically in this video we』ll be focusing on simple diffusion.

在關於細胞膜運輸這一部分中，我們將重點討論各種類型的膜運輸。在這段視頻中，我們將重點介紹簡單擴散。

And so when we look at this outline of membrane transport, we’re going to be focusing on movement of solutes—that is along a gradient. So these are all types of passive transport, and there are three types. 

當看到膜運輸的概述時，我們將關注溶質沿梯度運動。這些都是被動運輸的類型，有三種。

So the first type we’re going to be discussing is simple diffusion. You』ll have a separate video lecture for facilitated diffusion osmosis, primary active transport, and secondary active transport.

我們要討論的第一種類型是簡單擴散。將有一個單獨的視頻課程，講易化擴散滲透，一級主動運輸和二級主動運輸。

So before we even begin with this section, what I would like for you to do is to look at the various transport properties that are listed on this slide. For example: Spontaneous, not spontaneous, may or may not require a transmembrane protein. 

因此，在我們開始本節之前，我希望你先看看本幻燈片中列出的各種運輸特性。例如：自發的，非自發的，可能需要或可能不需要跨膜蛋白。

And what I want you to do for each of these properties is to decide—is that a property of passive transport or is that a property of active transport? And so please pause the video and then decide which of these properties belong to what type of transport. And so let’s go ahead and go through these, okay?

對於這些特性，我要你們作出判斷，它到底是被動運輸還是主動運輸？所以請暫停視頻，然後判斷這些特性中分別屬於哪種傳輸類型。讓我們開始通讀一下，好嗎？｜跨膜蛋白｜ 跨膜蛋白（transmembrane protein）是一種貫穿生物膜兩端的蛋白。許多跨膜蛋白的功能是作為通道或「裝載碼頭」來實施拒絕或允許某種特定的物質跨過生物膜的運輸、進入細胞，同時，也使要廢棄的副產品運出細胞。當對某種分子做出相應時，這些「負責運載」的跨膜蛋白通過特定的摺疊和彎曲方式，實現該分子的跨過生物膜的運輸。So I’m—I’m hoping that you』ve already paused the video and now you’re ready to check your answers. And so remember if we’re dealing with some sort of passive movement: Here’s a hill, I have a rock sitting up on top of a hill, okay? If it’s an active process, here’s my hill and I have a rock sitting down at the bottom of the hill.

我希望你已經暫停了視頻，現在準備好檢查你的答案了。記住，如果我們在探討某種被動運動：這裡有一座山，有一塊石頭在山頂上。如果這是一個主動的過程，這是我的山，我有一塊石頭在山的底部。

So a spontaneous property means that it’s just going to happen, right? So for example, this rock is just going to come down that hill on it’s own. Okay? So spontaneous is a form of passive transport. Now not spontaneous—it’s not spontaneous for this rock to automatically go up hill all on it’s own, right? It would need some help. So that’s an active process; it’s not spontaneous. 

所以自發的屬性意味著它會發生，對吧？舉個例子，這塊石頭會自己從山上下來。所以自發是一種被動的運輸方式。現在非自發的：這石頭不是純靠自己自動上山的，對吧？它需要幫助，所以這是一個主動的過程；不是自發的。

Now it may or may not require a transmembrane protein, that’s going to be for passive types of transport that we』ll discuss in a lot of detail here shortly, and then requires a transmembrane protein. That’s an active form. Okay?

可能需要或可能不需要跨膜蛋白，這是一種被動運輸，我們稍後將詳細討論，然後是需要跨膜蛋白。這是一種主動運輸。

Now, requiring energy: Would it require energy to push that rock up that hill? And the answer is yes. So active forms will require energy. Passive forms, on the other hand, don’t require any energy. It doesn’t take any energy for the rock to go down the hill, does it?

需要能量：把那塊石頭推上山需要能量嗎？答案是肯定的。所以主動運輸需要能量。而被動運輸，不需要能量。巖石下山不需要任何能量，不是嗎？

So passive forms do not require energy. So then we have a solute moving along a gradient. So when we talk about a solute moving along a gradient, then that means this rock is going from high concentration toward a low concentration. So along a gradient means high concentration toward a low concentration, okay? And that’s considered a passive process.

所以被動運輸不需要能量。然後是溶質沿梯度運動。當我們討論溶質沿梯度運動時，意味著巖石從高濃度走向低濃度。所以沿著梯度意味著從高濃度走向低濃度。這被認為是一個被動的過程。

Solutes that move against a gradient means that they’re going from a low concentration…toward a higher concentration, and that’s an active process. Okay, so now with those properties.

溶質逆梯度移動，這意味著它們從低濃度向高濃度移動，這是一個主動的過程。

in mind, let’s go ahead and we’re first going to be discussing simple diffusion. 

好吧，記住這些特性，讓我們繼續，首先討論簡單擴散。

So remember simple diffusion falls underneath of a passive type of transport, which automatically tells you your solute moves along a gradient and it automatically tells you that it does not require any energy. All right, so here we have a phospholipid bilayer, right, that’s making up the plasma membrane.

請記住，簡單擴散屬於被動的運輸類型，它自動告訴你溶質沿梯度移動，它自動告訴你它不需要任何能量。這裡我們有一個磷脂雙分子層，它構成了質膜（細胞膜）。

And we want to first off talk about solutes that can passively diffuse through a membrane. So if it’s simple diffusion, whatever solute I may have—we』ll just put 「x」 over here—this is my solute. This solute can freely diffuse through the membrane.我們首先要討論的是能跨膜被動擴散的溶質。如果這種溶質是簡單擴散，不管什麼溶質，我們就把「x」放在這裡，這是我的溶質。這種溶質可以跨膜自由擴散。That’s another way of saying that it has a high permeability, okay? It freely diffuses—a high permeability.

另一種說法是它有很高的滲透性。它可以自由擴散——高滲透性。

And so if you remember the structure of the phospholipid bilayer and the chemical makeup of the chemical makeup of the bilayer, it will help you understand why the solutes can freely diffuse.

如果你記得磷脂雙分子層的結構和化學組成，它將幫助你理解為什麼溶質可以自由擴散。

｜跨磷脂雙分子層｜ 磷脂雙分子層（phospholipid bilayer）是由兩層磷脂分子組成的薄膜。幾乎所有細胞生物的細胞膜和許多病毒的包膜都主要由磷脂雙分子層構成，此外，核被膜和許多胞器（如內質網等）也具有磷脂雙分子層。磷脂雙分子層在細胞中起屏障作用，使離子、蛋白質或其它物質保留在需要之處，阻止其擴散到其他地方，並阻止有害物質的進入。So remember that these tails, these tails here are fatty acids. FA: fatty acids. So these fatty acid tails are fat, they’re fats. So anything that’s fat soluble will freely diffuse through that membrane. 

記住這些尾部，它們是脂肪酸(FA)。這些脂肪酸尾部是脂肪。所以任何脂溶性的物質都能自由地跨膜擴散。

So if it’s fat soluble, a couple of terms for you to remember, that means it’s lipophilic. Phil or philic means 「to love.」

所以如果它是脂溶性的，有幾個術語需要記住，這意味著它是脂溶性的。Phil 或 philic 意思是 「喜歡」。

Lipo, 「fat.」 Okay? So fat-soluble substances are lipophilic. So if they love fat, they are going to be afraid of water. So they are going to be hydrophobic. So hydro is water, phobic: fear. So they fear water. Okay? 

Lipo, 「脂肪」。所以脂溶性物質是親脂的。如果他們喜歡脂肪，他們就會怕水。所以它們是疏水的。所以hydro就是水，hobic：懼怕。所以它們怕水。

Now keep in mind that water, if I draw out one water molecule for you, water molecules have partial charges: The hydrogens have positives, the oxygen has a negative. And so any molecule that’s non-polar means it has no partial charges.

現在請記住，我給你們畫一個，水分子，水分子有部分電荷（原子淨電荷）：氫有正電荷，氧有負電荷。任何非極性分子都意味著它沒有部分電荷。

So if there’s no partial charges, it is not attracted to water. So it’s afraid of water, Okay? We should maybe put a big red 「x」 there—it’s afraid of water.

如果沒有部分電荷，就不會被水吸引，所以它疏水。我們在那放一個大大的紅色「x」，表示它怕水。

So it’s hydrophobic. Okay, so what this is telling us then is that we have substances that can freely diffuse include: lipophilic substances, right? We』ve mentioned that already.

所以它是疏水的。好吧，那麼這告訴我們的是，我們有可以自由擴散的物質，包括：親脂性物質，對吧？我們已經提到過了。

Hydrophobic solutes, all right. Non-polar solutes, and then we have this question of, well, small and polar or large and polar? So the answer to this is that small polar molecules can actually freely diffuse the membrane even though they have partial charges, and that’s just because of their size;  they’re really small. So we have small polar molecules.

疏水性溶質，非極性溶質。然後我們有一個問題，小極性分子和大極性分子呢？答案是，小極性分子實際上可以自由地跨膜擴散，即使它們帶有部分電荷，能自由擴散只是因為它們的尺寸真的很小。所以小極性分子也是自由擴散的。

1)極性分子：正電荷中心和負電荷中心不相重合的分子2)非極性分子：正電荷中心和負電荷中心相重合的分子3)分子極性的判斷：分子的極性由共價鍵的極性及分子的空間構型兩個方面共同決定。（忘記共價鍵和空間構型的同學回去翻看高中化學書哦）An example of a small and polar molecule would be water that can freely diffuse.

Now, here’s the catch. This is a really important point for you to remember. In this course, if we are talking about water movement, meaning the diffusion of water, it, it is only going to be moving if there is aquaporin present and therefore we’re only talking about diffusion of water with osmosis. That will make working your molecular transport problems a lot simpler for you.

現在，這是關鍵。這一點對你來說非常重要。在這個課程中，如果我們討論的是水的運動，意思是水的擴散，它只有在水通道蛋白存在的情況下才會運動，所以我們說的只是滲透作用下的水的擴散。這將讓你在學習分子運輸問題上更簡單。

So again, if we talk about the diffusion of water, we are talking about osmosis. That is not simple diffusion, okay? Different concept.

同樣，如果我們談論水的擴散，我們談論的是滲透作用。這不是簡單擴散，好嗎？不同的概念。

All right, so that takes care of the solutes that can freely diffuse, and then since it’s simple diffusion, we know it’s a type of passive transport. 

好吧，這樣就理清了能自由擴散的溶質，既然它是簡單擴散，我們就知道它是一種被動運輸。

So that tells us that our solute is going to be moving…along a gradient…okay? Which is the same thing as saying down the gradient—which is the same thing as saying from a high concentration toward a low concentration.

所以這告訴我們，溶質將沿梯度移動。"沿梯度移動"和"降梯度移動"是一個意思，和「從高濃度到低濃度」也是一個意思。

So let’s practice. So pause the video, and then answer this question. The solute is the green dot.

所以讓我們練習一下。暫停視頻，然後回答這個問題。溶質是綠點。

It’s a lipid soluble molecule. Okay, so I’m assuming you』ve already paused the video and we want to know in which direction will the solute diffuse? 

它是一個脂溶性分子。好吧，我假設你已經暫停了視頻，我們想知道溶質會向哪個方向擴散？

So this is a lipid-soluble molecule, meaning it’s lipophilic, right, and hydrophobic. So we know it can freely diffuse.

這是一種脂溶性分子，意味著它是親脂的，疏水的。所以我們知道它可以自由擴散。

Okay. So when we look at the concentration, we know that there’s a high concentration of the solute inside the cell. There’s a low concentration outside of the cell.

當我們觀察濃度時，我們知道細胞內有高濃度的溶質。而細胞外的濃度很低。

So wherever you have a higher concentration, there』ll be a greater frequency of collisions,right, amongst those solutes. The more collisions you have, the more energy that gets created, and hence you’re going to drive those solutes across the membrane.

無論你在哪裡，濃度越高，碰撞頻率就越高，在這些溶質中（也是）。碰撞的次數越多，產生的能量就越多，因此將驅動這些溶質穿過細胞膜。

Okay, so this solute is going to be moving out of the cell, which is the same thing as saying it’s moving into the extracellular fluid.

所以說「這個溶質會移出細胞」，這和說「它會進入細胞外液」是一個意思。

So the correct answer for this is option D. 

所以正確的答案是選項D。