I mentioned earlier, we thought about receptors as being these blocks and membranes but there are different families of receptors.

我之前讲过,我们把受体看做一类,固定在细胞膜上的分子,但受体有许多不同家族

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These are molecules that exist naturally in cell membranes and are activated by certain enzymes and kinases generated by receptors.

这些分子存在于细胞膜表面,能被受体激活的某种酶或激酶所活化

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It can't enter cells because it's too big and it's too water soluble so it can't go through cell membranes.

它的分子太大了所以无法进入细胞,而且还是水溶性的,所以它也无法穿过细胞膜

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So most of the lipids, which make up cell membranes in your body are of this category of phospholipids.

大部分脂类,那些在你体内构成细胞膜的脂类,都属于磷脂类

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Many of them are derived from cholesterol and they're hydrophobic, which means they can penetrate through cell membranes.

多数分子都来自于胆固醇,它们是疏水性的,这意味着它们能够穿过细胞膜

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There's lipid chains in between so cell membranes are lipid rich layers that can exist in water.

脂质链在两者中间,所以细胞膜是富含脂类的膜层,并可以稳定存在于水中

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If a cell membrane was indeed just a lipid bilayer, then glucose could never enter the cell because it can't permeate through cell membranes.

如果细胞膜只是一个脂质双分子层的话,葡萄糖就不可能进入细胞,因为它不能渗透过细胞膜

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All cell membranes have these channels within them, and under their resting conditions sodium is moving from outside to inside, potassium's moving from inside to outside.

所有细胞膜上都有这种通道结构,在静息状态下,钠从细胞外流向细胞内,钾从细胞内流向细胞外

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I'll talk about biological membranes and lipids and how they're assembled.

我会讲到生物膜和脂质,及它们是如何组装成质膜的

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another thing that you'd find if you looked inside the axon terminals of any of these pre-synaptic membranes, you'd find lots of vesicles or some membrane bound compartments that contain special chemicals called neurotransmitters.

如果你仔细观察,突触前膜的轴突末梢内部,你会发现很多小泡,即膜包被的结构,包含有称为神经递质的特殊化合物

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All membranes are electrically charged.

所有的膜都是带电的

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Now, sodium and potassium don't ordinarily move across membranes, they're charged molecules, they can't dissolve, they can't permeate through a cell membrane, but they go through because there are channels that allow them to pass through in the membrane.

钠和钾通常是不能跨过细胞膜的,它们都是带电粒子,它们不能溶解在细胞膜中,不能渗透通过细胞膜,但它们之所以能通过细胞膜,全赖膜上离子通道的作用

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Now that's not the only thing in cell membranes, there are also proteins in cell membranes, and these proteins are special proteins that can exist within membranes like this, and they exist because these proteins also have different segments with different properties.

但细胞膜并不只由磷脂构成,细胞膜里还有蛋白质,而且这些蛋白质是一些,可以在细胞膜中存在的特殊的蛋白质,而这些蛋白质存在于细胞膜中,源于它们也有溶解性不同的片段

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I do want to talk about one important subject which you might not have thought too much about and that's lipids, because lipids are so important to the structure of the body because they make up the membranes that form the cells that are the fundamental units.

我的确想要讨论一个重要的主题,这个主题也许你们都没有深入思考过,那就是关于脂类的问题,脂类对身体结构形成十分重要,它是组成细胞膜的基本单位,而细胞膜能够维持细胞形态

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So you form DNA lipid complexes and because the DNA is complexed with lipids it's more soluble in membranes and more likely to enter cells.

形成DNA脂类复合体之后,因DNA同脂类复合,其脂溶性大大增加,更容易进入细胞

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We talked about this a little bit in section last week, when you eat vegetables or meat, you're eating a lot of DNA but that doesn't enter the cells of your body because of the barrier properties of cell membranes.

这个我们上周讨论会讲过一些,我们在吃蔬菜或者肉类时,摄入了大量DNA,它们之所以不会进入你的体细胞,就是由于细胞膜的这种屏障作用

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