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  • Cell membranes are structures of contradictions.

    細胞膜是種充滿矛盾的結構

  • These oily films are hundreds of times thinner than a strand of spider silk,

    這些油膜比一縷蜘蛛絲薄上數百倍

  • yet strong enough to protect the delicate contents of life:

    然而強韌至足以保護 生命精緻的內含物質:

  • the cell's watery cytoplasm, genetic material, organelles,

    質地似水的細胞質、 遺傳物質、細胞器

  • and all the molecules it needs to survive.

    以及賴以生存的所有分子

  • How does the membrane work, and where does that strength come from?

    細胞膜是如何運作 以及從哪裡獲得力量?

  • First of all, it's tempting to think of a cell membrane

    首先,我們很容易把細胞膜

  • like the tight skin of a balloon,

    想成氣球繃緊的外膜

  • but it's actually something much more complex.

    但它確實比這複雜多了

  • In reality, it's constantly in flux,

    事實上,它不斷地流動

  • shifting components back and forth to help the cell take in food,

    來回移動各種組成 以幫助細胞攝食

  • remove waste,

    移除廢物

  • let specific molecules in and out,

    讓特定分子進出細胞

  • communicate with other cells,

    與其他細胞溝通

  • gather information about the environment,

    收集有關環境的訊息

  • and repair itself.

    以及自我修復

  • The cell membrane gets this resilience, flexibility, and functionality

    細胞膜具有回彈性 柔靭性及功能性

  • by combining a variety of floating components

    是因為它結合各種流動的成分

  • in what biologists call a fluid mosaic.

    這就是生物學家 所謂的「流動鑲嵌模型」

  • The primary component of the fluid mosaic

    流動鑲嵌模型的主要組成

  • is a simple molecule called a phospholipid.

    是一種簡單的分子稱為「磷脂」

  • A phospholipid has a polar, electrically-charged head,

    磷脂具有極性、帶電的頭端

  • which attracts water,

    能吸引水

  • and a non-polar tail, which repels it.

    而不具極性的尾端則排斥水

  • They pair up tail-to-tail in a two layer sheet

    它們尾端對尾端配對 形成兩層的薄面

  • just five to ten nanometers thick that extends all around the cell.

    只有 5-10 nm 的厚度 環繞整個細胞

  • The heads point in towards the cytoplasm

    頭端朝內指向細胞質

  • and out towards the watery fluid external to the cell

    及朝外指向細胞外面的液體

  • with the lipid tails sandwiched in between.

    而脂質的尾端則夾在其間

  • This bilayer, which at body temperature has the consistency of vegetable oil,

    這脂質雙層在體溫下 具有植物油的黏稠度

  • is studded with other types of molecules,

    且鑲嵌其他多種分子

  • including proteins,

    包括蛋白質

  • carbohydrates,

    碳水化合物

  • and cholesterol.

    和膽固醇

  • Cholesterol keeps the membrane at the right fluidity.

    膽固醇讓膜保持適度的流動性

  • It also helps regulate communication between cells.

    也幫助調節細胞間的溝通

  • Sometimes, cells talk to each other

    有時,細胞能相互交談

  • by releasing and capturing chemicals and proteins.

    是藉著化學物質 與蛋白質的釋放與捕捉

  • The release of proteins is easy,

    釋放蛋白質很容易

  • but the capture of them is more complicated.

    但捕捉它們則比較複雜

  • That happens through a process called endocytosis

    那是經由「胞吞」的方式進行

  • in which sections of the membrane engulf substances

    即部分細胞膜包吞物質

  • and transport them into the cell as vesicles.

    然後形成小囊泡 將它們送入細胞內

  • Once the contents have been released,

    一旦內含物被釋出

  • the vesicles are recycled and returned to the cell membrane.

    小囊泡則被回收 重新回到細胞膜

  • The most complex components of the fluid mosaic are proteins.

    流動鑲嵌模型最複雜的成分是蛋白質

  • One of their key jobs is to make sure

    它們其中一個關鍵功用

  • that the right molecules get in and out of the cell.

    是確保正確的分子進出細胞

  • Non-polar molecules, like oxygen,

    非極性分子,例如氧

  • carbon dioxide,

    二氧化碳

  • and certain vitamins

    和某些維生素

  • can cross the phospholipid bilayer easily.

    能輕易地通過磷脂雙層

  • But polar and charged molecules can't make it through the fatty inner layer.

    但極性、帶電分子 則無法通過脂質內層

  • Transmembrane proteins stretch across the bilayer to create channels

    「跨膜蛋白」跨過 整個脂質雙層而形成通道

  • that allow specific molecules through, like sodium and potassium ions.

    能讓特定的分子通過 如鈉和鉀離子

  • Peripheral proteins floating in the inner face of the bilayer

    浮在脂質雙層內側的「膜周邊蛋白」

  • help anchor the membrane to the cell's interior scaffolding.

    會協助細胞膜 固定於細胞的內支架

  • Other proteins in cell membranes can help fuse two different bilayers.

    細胞膜上的其他蛋白質 能協助融合兩個不同的雙層

  • That can work to our benefit, like when a sperm fertilizes an egg,

    這能有利於我們 如精子使卵子受精

  • but also harm us, as it does when a virus enters a cell.

    但也能傷害我們 例如病毒侵入細胞時

  • And some proteins move within the fluid mosaic,

    有些蛋白質 在流動鑲嵌模型的裡面流動

  • coming together to form complexes that carry out specific jobs.

    聚集形成執行特殊任務的複合物

  • For instance, one complex might activate cells in our immune system,

    例如一種複合物 能激活免疫系統的細胞

  • then move apart when the job is done.

    當任務結束後就分開

  • Cell membranes are also the site of an ongoing war

    細胞膜也是一個我們 和所有感染物之間的戰場

  • between us and all the things that want to infect us.

    事實上,我們知道一些最毒的物質

  • In fact, some of the most toxic substances we know of

    是由感染細菌製造的破膜蛋白質

  • are membrane-breaching proteins made by infectious bacteria.

    這些「形成微孔毒素」 在細胞膜上戳出大洞

  • These pore-forming toxins poke giant holes in our cell membranes,

    導致細胞內含物漏出去

  • causing a cell's contents to leak out.

    科學家們正在研發對抗它們的方法

  • Scientists are working on developing ways to defend against them,

    如使用一種奈米海綿 來解救細胞

  • like using a nano-sponge that saves our cells

    它能吸取破壞細胞膜的毒素

  • by soaking up the membrane-damaging toxins.

    流動鑲嵌模型使得 所有生命的功能變得可能

  • The fluid mosaic is what makes all the functions of life possible.

    缺了細胞膜,細胞將不存在

  • Without a cell membrane, there could be no cells,

    缺了細胞,就沒有細菌

  • and without cells, there would be no bacteria,

    沒有寄生蟲、黴菌及動物

  • no parasites,

    也就沒有我們了

  • no fungi,

  • no animals,

  • and no us.

Cell membranes are structures of contradictions.

細胞膜是種充滿矛盾的結構

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B2 中高級 中文 美國腔 細胞膜 細胞 鑲嵌 分子 脂質 蛋白質

細胞膜 (Cell membranes are way more complicated than you think - Nazzy Pakpour)

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    劉源清   發佈於 2020 年 01 月 07 日
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