Name: how lipid molecules are built
Uploaded: 2023-04-30T18:28:47.000Z
Duration: 3 min 38 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Life Science

SC.912.L.18

SC.912.L.18.1

Structure of Lipids

脂类是一组疏水分子，包括用于储存能量的甘油三酸酯 和作为细胞膜主要结构成分的 磷脂。甘油三酸酯和大多数磷脂 由甘油和脂肪酸链组成。脂肪酸在链的一端带有甲基，在另一端带有羧基。与羧基连接的碳 称为阿尔法碳，而甲基碳 称为欧米茄 碳。脂肪酸的长度不同，并且在烃链中存在双键。带有双键的链是不饱和脂肪酸，只有单键的链是饱和脂肪酸，因为它们被尽可能多的氢原子所 饱和。脂肪酸通常具有通用名称，但可以根据碳原子的数目 和碳链上双键的数目和位置 来系统命名。有几种常见的编号方法。羧基参照系统计算 羧基碳上所有双键的位置，羧基碳编号为 1。欧米茄参照系统计算 最接近欧米茄碳的双键位置，欧米茄碳编号为 1。例如，亚麻酸是一种欧米茄 3-脂肪酸，它有 18 个碳，从羧基端算起，在第 9、12 和 15 位有双键。根据羧基参照系统，它称为 18:3Δ9，12，15，根据欧米茄参照系统，它称为 18:3 不饱和脂肪酸有两种构型：顺式和反式。在顺式构型中，双键中碳上的氢 位于键的同一侧，而在反式构型中，氢则位于相反的一侧。从结构上看，顺式脂肪酸是弯曲链，反式脂肪酸是直链。人们发现，摄入反式脂肪 会导致各种心血管疾病，而摄入顺式脂肪酸，例如欧米茄-3 和欧米茄-6，则对健康有益。甘油三酯，俗称脂肪，主要用于储存能量。它们由三种脂肪酸组成，通过甘油羟基端 和脂肪酸羧基端之间的酯键 与甘油相连，形成非极性分子。如果所有三种脂肪酸都属于同一类型，它们就称为简单甘油三酯。如果这三种脂肪酸不同，则称为混合甘油三酯。磷脂是另一种类型的脂质，它是生物膜的 重要结构特征。它们具有 由亲水性醇基团修饰的磷酸基团构成的亲水头，和由脂肪酸链构成的疏水尾 这些头和尾的组成可以变化，产生不同类型的膜脂。甘油磷脂是一种常见的磷脂类型，由两个脂肪酸和一个高极性基团组成，分别通过酯和磷酸二酯键 连接到甘油的每个碳上。

脂质的结构

脂质包括多种化合物，这些化合物在本质上基本上是非极性的。 这是因为碳氢化合物主要包括非极性碳或碳氢键。 非极性分子具有疏水性 (“担心水”) ，或在水中不溶解。 脂质在细胞中执行许多不同的功能。 细胞存储能量以脂肪形式长期使用。 脂质还可为植物和动物提供环境绝缘。 例如，它们有助于保持水生鸟类和哺乳动物的干燥，因为它们具有防水疏水性，所以在毛皮或羽毛上形成保护层。 脂质也是许多荷尔蒙的组成部分，是所有细胞膜的重要组成部分。 脂质包括脂肪，油，蜡，磷脂和类固醇。 
 脂质的一般结构 
 脂肪分子由两个主要成分组成—甘油和脂肪酸。 甘油是一种有机化合物 (酒精) ，含有三种碳，五种氢原和三种氢氧基 (OH) 组。 脂肪酸有一条长长的碳氢化合物链，碳氧合物组附在该链上，因此其名称为“脂肪酸”。 脂肪酸中的碳氢化合物数量可能介于 4 到 36 之间。 最常见的是含有 12 – 18 种碳化合物的碳化合物。 在脂肪分子中，脂肪酸通过氧原子附着在甘油分子的三种碳中，其中一种是酯键。 在脱水反应中将三种脂肪酸加入甘油主干，形成三氯甘油。 三氯甘油中的三种脂肪酸可能相似或不同。 
 磷脂是另一种常见的脂质。 它是一种对等分子，意味着它具有疏水性和亲水成分。 脂肪酸链具有疏水性，不能与水相互作用；而含磷酸盐的组则具有亲水性，并与水相互作用。 磷脂的亲水头组面对水溶液。 疏水尾被固定在胆管中间。 
 脂肪酸 
 脂肪酸可能已饱和或未饱和。 在脂肪酸链中，如果碳氢化合物链中相邻碳化合物之间只有单键，则脂肪酸会饱和。 硬脂酸是饱和脂肪酸的一个示例。 
 当碳氢化合物链中含有双键时，脂肪酸将不饱和。 油酸是未饱和脂肪酸的一个示例。 大多数不饱和脂肪在室温下是液体，称为油。 如果分子中有一个双键，那么它是一种单饱和脂肪 (例如橄榄油) ，如果有多个双键，那么它是一种多饱和脂肪 (例如，油)。 长直型脂肪酸，带单键，通常袋子紧密，在室温下是固体的。 动物脂肪中含有硬脂酸和棕榈酸 (肉类中常见) ，脂肪中含有丁酸 (黄油中常见) ，这是饱和脂肪的示例。 
 此外，脂肪酸还可以被分类为 CIS 和 TRANS。 CIS 和 TRANS 指示双键周围分子的配置。 如果氢原存在于同一平面中，则为 CIS 脂肪。 如果氢原子位于两个不同的平面上，则它是一种转运脂肪。 CIS 双键会导致弯曲或“扭结”，从而阻止脂肪酸与堆积紧密相连，从而使它们在室温下保持液体流动。 橄榄油，玉米油，油菜籽油和鳕鱼肝油是不饱和脂肪的例子。 不饱和脂肪有助于降低血液胆固醇水平；而饱和脂肪则有助于动脉中形成斑块。 
 反式脂肪 
 食品行业人为地对油进行氢化处理，使其半固化，并具有许多加工食品生成物所需的一致性。 在此过程期间，碳氢化合物链中 CIS –构象的双键可能会在 Trans –构象中转换为双键。 
 人造黄油（Margarine麦淇淋） ，一些类型的花生酱和缩短是人工氢化反式脂肪的示例。 最近的研究表明，人类饮食中反式脂肪的增加可能导致低密度脂蛋白 (LDL) 或“不良”胆固醇水平升高，进而导致动脉中的斑块气相沉积，从而导致心脏病。 
 Omega 脂肪酸 
 必需脂肪酸是人体需要的，但不合成。 因此，必须通过饮食摄入来补充这些食物。 Omega-3 脂肪酸属于这一类，是人类已知的两种产品之一 (另一种是 Omega-6 脂肪酸)。 这些是多聚不饱和脂肪酸，是 omega-3 ，因为双键将碳氢化合物链端的第三个碳与其邻近的碳连接起来。 
 Alpha-亚麻酸 是 omega-3 脂肪酸的一个示例。 它有三个 CIS 双键，因此是弯曲的形状。 鲑鱼，鳟鱼和金枪鱼是 omega-3 脂肪酸的好来源。 研究表示， omega-3 脂肪酸通过抑制血液凝结减少心脏病突发死亡的风险，降低血液中甘油三酯的含量，降低血压，并防止血栓形成。 它们还可以减少炎症，并有助于降低动物中某些癌症的风险。 
 本文改编自 <a href="https://openstax.org/books/biology-2e/pages/3-3-lipids"> Openstax, 生物学 2e, 第 3.3 章：脂质</a>。

脂质包含一大类性质上主要为非极性的化合物。这是因为它们是主要由非极性碳氢化合物组成的烃类……

Education

教育

JoVE Core

Cell Biology

细胞生物学

Unit 1

第一单元

Biochemistry of the Cell

细胞生物化学

KEY TERMS AND CONCEPTS

关键术语与概念

how lipid molecules are built

Lipid molecules are built from hydrocarbon chains and a few key structural parts. Their shape helps explain why they behave differently from many other biological molecules. In high school biology, this structure is often linked to how lipids store energy and help form cell membranes.

Some lipids are made from fatty acids joined to other small molecules. Triglycerides contain glycerol and three fatty acids, while phospholipids contain glycerol, two fatty acids, and a phosphate group. These structural differences give each type a different role in living things.

Fatty acids can also differ from one another. Saturated fatty acids have only single bonds between carbon atoms, while unsaturated fatty acids have one or more double bonds. These bond patterns change the way lipid molecules pack together and help explain their physical properties.

How Lipid Molecules Are Built

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SC.912.L.18.7

A. All living things are composed of four basic categories of macromolecules and share the same basic needs for life.

B. Living organisms acquire the energy they need for life processes through various metabolic pathways (primarily photosynthesis and cellular respiration).

C. Chemical reactions in living things follow basic rules of chemistry and are usually regulated by enzymes.

D. The unique chemical properties of carbon and water make life on Earth possible.

How Lipid Molecules Are Built

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