4.4 等离子膜
章节大纲
-
A Bag Full of Jell-O
::装满果冻的袋子This simple cut-away model of an shows that a cell resembles a plastic bag full of Jell-O. Its basic structure is a plasma membrane filled with cytoplasm . Like Jell-O containing mixed fruit ( see the photo ), the cytoplasm of the cell also contains various structures, including a a and other . Your body is composed of trillions of cells, but all of them perform the same basic life functions. They all obtain and use energy , respond to the environment, and reproduce. How do your cells carry out these basic functions and keep themselves — and you — alive? To answer these questions, you need to know more about the structures that make up cells, starting with the plasma membrane.
::这个简单的切除模型显示一个细胞类似于一个装满果冻的塑料袋。 它的基本结构是装满细胞板块的等离子膜。 就像含有混合水果的果冻(见照片)一样, 细胞的细胞板块也包含各种结构, 包括一个和其他结构。 你的身体由数万亿个细胞组成, 但是它们都具有相同的基本生命功能。 它们都获得和使用能量, 对环境作出反应, 并繁殖。 你的细胞如何执行这些基本功能, 并保持生命—— 而你呢? 要回答这些问题, 您需要更多地了解构成细胞的结构, 从等离子膜开始。These Jell-O molds containing mixed fruit make a tasty model of your cells.
::这些果冻模具 含有混合果实 制作了一个美味的细胞模型What is the Plasma Membrane?
::等离子膜是什么?The plasma membrane is a structure that forms a barrier between the cytoplasm inside the cell and the environment outside the cell. Without the plasma membrane, there would be no cell. Although it is very thin and flexible, the plasma membrane protects and supports the cell by controlling everything that enters and leaves it. It allows only certain substances to pass through, while keeping others in or out. To understand how the plasma membrane controls what passes into or out of the cell, you need to know its basic structure.
::等离子膜是一种结构,它构成细胞内细胞细胞与细胞外环境之间的屏障。没有等离子膜,就不会有细胞。尽管等离子膜非常薄和灵活,但血浆膜通过控制所有进出细胞的物质来保护和支撑细胞。它只允许某些物质通过,同时让其他人进出。为了了解等离子膜如何控制细胞的进出,你需要了解细胞的基本结构。Phospholipid Bilayer
::磷磷脂The plasma membrane is composed mainly of phospholipids, which consist of fatty acids and alcohol. The phospholipids in the plasma membrane are arranged in two layers, called a . As shown in the diagram , each phospholipid molecule has a head and two tails. The head “loves” (hydrophilic) and the tails “hate” water (hydrophobic). The water-hating tails are on the interior of the membrane, whereas the water-loving heads point outward, toward either the cytoplasm or the fluid that surrounds the cell.
::等离子膜主要由磷素组成,由脂肪酸和酒精组成。等离子膜中的磷素分为两层,称为a。如图所示,每个磷素分子有一个头和两个尾部。头部(水利)和尾部(缺水)为“缺水”水。防水尾部在膜内,而热水头向外指向细胞周围的细胞板块或液体。Molecules that are hydrophobic can easily pass through the plasma membrane if they are small enough, because they are water-hating like the interior of the membrane. Molecules that are hydrophilic , on the other hand, cannot pass through the plasma membrane — at least not without help — because they are water-loving like the exterior of the membrane.
::缺乏水分的分子很容易通过等离子膜,如果它们足够小的话,因为它们像膜的内部一样防水,而具有水利作用的分子则不能通过等离子膜——至少没有帮助——因为它们像膜的外部一样热爱水。
Phospholipid Bilayer. The phospholipid bilayer consists of two layers of phospholipids, with a hydrophobic (water-hating) interior and a hydrophilic (water-loving) exterior. The hydrophilic (polar) head group and hydrophobic tails (fatty acid chains) are depicted in the single phospholipid molecule. The polar head group and fatty acid chains are attached by a 3-carbon glycerol unit.
::磷素脂双层磷素由两层磷素组成,内部有防水(防水)的内部,外体有水利(爱水)的外体,单磷素分子中描绘了水利(极)头组和防水尾(脂肪酸链),极地头组和脂肪酸链由一个3碳甘油单位连接。Other Molecules in the Plasma Membrane
::Plasma 膜中的其他分子The plasma membrane also contains other molecules, primarily other and . The green molecules in the diagram , for example, are the lipid cholesterol. Molecules of the steroid lipid cholesterol help the plasma membrane keep its shape. P roteins in the plasma membrane include transport proteins that assist other substances in crossing the cell membrane, receptor s that allow the cell to respond to chemical signals in its environment, and cell-identity markers that indicate what type of cell it is and whether it belongs in the body.
::等离子膜还含有其他分子,主要是其他分子和。例如,图表中的绿色分子是脂质胆固醇。类固醇的摩尔胆固醇有助于等离子膜保持其形状。等离子膜中的蛋白质包括帮助其他物质跨过细胞膜的运输蛋白质、允许细胞对其环境中的化学信号作出反应的受体,以及表明细胞属于何种细胞以及细胞是否属于身体的细胞识别标记。Additional Functions of the Plasma Membrane
::Plasma 膜的附加功能The plasma membrane may have extensions, such as whip-like flagella (singular flagellum) or brush-like cilia (singular cilium), shown , that give it other functions. In single-celled organisms , these membrane extensions may help the organisms move. In , the extensions have different functions. For example, the cilia on human lung cells sweep foreign particles and mucus toward the mouth and nose , while the flagell um on a human cell allows it to swim.
::等离子膜可能具有延伸作用,例如显示像鞭子一样的旗子(单)或像梳子一样的硅(单),这给了它其他功能。在单细胞生物中,这些膜延伸可能帮助生物运动。在其中,扩展具有不同的功能。例如,人体肺细胞上的硅将外来微粒和粘结扫向嘴和鼻子,而人类细胞上的允许它游泳。Human sperm with their long, whip-like flagella
::人类精子和长长的 鞭子般的旗子Brush-like cilia on lung epithelial cells
::肺上皮细胞上像粉刷般的青刷西里雅Feature: My Human Body
::特质:我的人体If you smoke and need another reason to quit, here's a good one. We usually think of lung as the major disease caused by smoking. But smoking can have devastating effects on the body's ability to protect itself from repeated, serious respiratory infections, such as bronchitis and pneumonia .
::如果你吸烟,需要另一个理由戒烟,这里有一个好理由。我们通常认为肺是吸烟引起的主要疾病。但是吸烟可能会对身体保护自己免受诸如支气管炎和肺炎等反复严重呼吸道感染的能力产生破坏性影响。Cilia are microscopic, hair-like projects on cells that line the respiratory, reproductive, and digestive systems. Cilia in the line most of your airways, where they have the job of trapping and removing dust, germs, and other foreign particles before they can make you sick. Cilia secrete mucus that traps particles, and they move in a continuous wave-like motion that sweeps the mucus and particles upward toward the throat, where they can be expelled from the body. When you are sick and cough up phlegm, that's what you are doing.
::Cilia是细胞上的显微镜,毛发相似的项目,它们与呼吸、生殖和消化系统相连接。Cilia在大部分的空气线线上,它们的工作是捕捉和清除尘埃、细菌和其他外来微粒,然后才能让你生病。Cilia 秘密粘结,它会捕捉粒子,它们以波状的连续运动向上移动,将粘液和微粒扫向喉咙,可以将其从身体中驱离。当你生病并咳嗽到血腿时,这就是你正在做的。Smoking prevents cilia from performing these important functions. Chemicals in tobacco smoke paralyze the cilia so they can't sweep mucus out of the airways. Those chemicals also inhibit the cilia from producing mucus. Fortunately, these effects start to wear off soon after the most recent exposure to tobacco smoke. If you stop smoking, your cilia will return to normal. Even if prolonged smoking has destroyed cilia, they will regrow and resume functioning in a matter of months after you stop smoking.
::吸烟阻止了cilia 发挥这些重要功能。 烟草烟雾中的化学物质使cilia 瘫痪, 从而无法从空气中扫出粘液。 这些化学物质也阻止cilia 生产粘液。 幸运的是, 这些效应在最近一次接触烟草烟雾之后很快开始消失。 如果您停止吸烟, 您的cilia就会恢复正常。 即使长期吸烟破坏了cilia, 它们也会在戒烟几个月后重新生长并恢复功能。Summary
::摘要-
The plasma membrane is a structure that forms a barrier between the cytoplasm inside the cell and the environment outside the cell. It allows only certain substances to pass in or out of the cell.
::等离子膜是一种结构,在细胞内部的细胞托盘与细胞外的环境之间形成屏障,只允许某些物质进入或离开细胞。 -
The plasma membrane is composed mainly of a bilayer of phospholipid molecules. It also contains other molecules, such as the steroid cholesterol — which helps the membrane keep its shape — and transport proteins, which help substances pass through the membrane.
::等离子膜主要由两层磷素分子组成,还含有其他分子,如类固醇胆固醇(帮助膜保持其形状)和转移蛋白质(帮助物质通过膜)。 -
The plasma membranes of some cells have extensions that have other functions, like flagella to help
sperm
move, or cilia to help keep our airways clear.
::一些细胞的等离子膜有其他功能的延伸,如帮助精子移动的白旗,或帮助保持空气通畅的硅亚。
Review
::回顾1. What are the general functions of the plasma membrane?
::1. 等离子膜的一般功能是什么?2. Describe the phospholipid bilayer of the plasma membrane.
::2. 描述等离子膜的磷素双层。3. Identify other molecules in the plasma membrane. State their functions.
::3. 查明等离子膜中的其他分子,说明其功能。4. Why do some cells have plasma membrane extensions, like flagella and cilia?
::4. 为什么有些细胞有血浆膜延展,如白旗和西里雅?5. Explain why hydrophilic molecules cannot easily pass through the cell membrane. What type of molecule in the cell membrane might help hydrophilic molecules pass through it?
::5. 解释为什么流益分子不能轻易通过细胞膜,细胞膜中哪种分子可以帮助流益分子通过细胞膜?6. Which part of a phospholipid molecule in the plasma membrane is made of fatty acid chains? Is this part hydrophobic or hydrophilic?
::6. 等离子膜中的磷素分子的哪一部分是由脂肪酸链制成的?这是疏水还是水利?7. The two layers of phospholipids in the plasma membrane are called a phospholipid ____________.
::7. 血浆膜中的两层磷素被称为磷素。8. True or False: The flagella on your lung cells sweep foreign particles and mucus toward your mouth and nose.
::8. 真实或假:肺细胞上的旗子将外国微粒和粘液扫向你的嘴和鼻子。9. True or False: Small hydrophobic molecules can easily pass through the plasma membrane.
::9. 真实或假:小型疏水分子很容易通过等离子膜。10. True or False: The side of the cell membrane that faces the cytoplasm is hydrophilic.
::10. 真实的或假的:面对细胞顶层的细胞膜的侧面是水利的。11. Steroid hormones can pass directly through cell membranes. Why do you think this is the case?
::11. 类固醇激素可以直接通过细胞膜,你认为为什么会这样?12. Some antibiotics work by making holes in the plasma membrane of bacterial cells. How do you think this kills the cells?
::12. 有些抗生素通过在细菌细胞的等离子膜上打洞而起作用,你认为这如何杀死细胞?13. What is the name of the long, whip-like extensions of the plasma membrane that helps some single-celled organisms move?
::13. 帮助某些单细胞生物移动的等离子膜长长、鞭状扩展体的名称是什么?Explore More
::探索更多Watch the video below to learn about the discovery of cell membranes' structure.
::看下面的录像 了解细胞膜结构的发现Watch the video below to learn about the function and structure of flagella and cilia.
::了解Fagella和cilia的功能和结构。 -
The plasma membrane is a structure that forms a barrier between the cytoplasm inside the cell and the environment outside the cell. It allows only certain substances to pass in or out of the cell.
