膽固醇是動(dòng)物組織的主要類固醇成分，也是血漿和幾乎所有細(xì)胞膜的正常成分。膽固醇是一種帶活性羥基的疏水的烴化合物。它是在C-17位置上帶有脂族側(cè)鏈的3-羥基固醇(具有全氫-1，2-環(huán)戊烯基菲環(huán)骨架)。理論上，膽固醇通過在膜的磷脂之間形成一插入結(jié)構(gòu)，從而在調(diào)節(jié)細(xì)胞膜的透過性和流動(dòng)性方面起重要作用。

膽固醇或游離存在或與脂肪酸結(jié)合成酯存在。膽固醇和膽固醇酯以脂蛋白形式運(yùn)輸，各種脂蛋白所含膽固醇的量不一，以低密度脂蛋白含量最高。生物膜中的膽固醇可以調(diào)整膜的流動(dòng)性以適應(yīng)不同的功能要求。

膽固醇是由 A、B和C等三個(gè)六碳環(huán)和一個(gè)五碳環(huán)D合并而成的環(huán)戊烷多氫菲衍生物，共含27個(gè)碳原子。環(huán)間相互以反式連接，通常取穩(wěn)定的椅式構(gòu)像。膽固醇除在5及6位碳之間有雙鍵外，其余的碳多為氫所飽和（故稱“多氫”）。各個(gè)碳原子的編號(hào)如下圖所示，式中按慣例略去氫原子，CH3基也只以短線表示，如18、19、21、26和27位碳甲基。3位碳上有一個(gè)羥基，17位碳上是1條八碳側(cè)鏈。環(huán)戊烷并菲核心為板狀剛性結(jié)構(gòu)，在其上的一端是具撓性的八碳側(cè)鏈，而在其另一端是羥基。

Cholesterol is the main steroid component of animal tissues and a normal component of plasma and almost all cell membranes. Cholesterol is a hydrophobic hydrocarbon compound with active hydroxyl groups. It is a 3-hydroxysterol with an aliphatic side chain at the C-17 position (with a perhydrogen-1,2-cyclopentenyl phenanthrene ring skeleton). Theoretically, cholesterol plays an important role in regulating the permeability and fluidity of the cell membrane by forming an insertion structure between the phospholipids of the membrane.

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Cholesterol exists either free or in combination with fatty acids to form esters. Cholesterol and cholesterol esters are transported in the form of lipoproteins. The amount of cholesterol in various lipoproteins is different, and the content of low-density lipoprotein is the highest. Cholesterol in the biofilm can adjust the fluidity of the membrane to meet different functional requirements.

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Cholesterol is a cyclopentane dihydrophenanthrene derivative composed of three six carbon rings a, B and C and one five carbon ring D. It contains a total of 27 carbon atoms. The rings are connected to each other in a reverse manner, usually in a stable chair configuration. Except that there are double bonds between the carbons at positions 5 and 6 of cholesterol, most of the remaining carbons are saturated with hydrogen (hence the name "polyhydrogen"). The numbering of each carbon atom is shown in the figure below. In the formula, hydrogen atom is omitted as usual, and CH3 group is only represented by short lines, such as carbomethyl groups at positions 18, 19, 21, 26 and 27. There is a hydroxyl group on the carbon 3 and an eight carbon side chain on the carbon 17. Cyclopentane phenanthrene core is a plate-like rigid structure, with a flexible eight carbon side chain at one end and a hydroxyl group at the other end.

取用前需放置室溫后再打開包裝取用防止吸潮，吸潮后活性會(huì)降低直至完全失去活性，請(qǐng)務(wù)必保持干燥，同時(shí)盡量避免頻繁的溶解和凍干。

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