Lipids - 高级

Oil doesn't mix with water, but why is this important, biologically speaking?
::石油不与水混合 但从生物学角度来说,这为什么重要?

Oil is a lipid. The property of chemically not being able to mix with gives lipids some very important biological functions. A particular type of lipid - the phospholipid - is the main component of the outer membrane of all . Why?
::石油是一种脂质,化学上无法与脂质混合的特性使脂质具有一些重要的生物功能。 一种特殊的脂质 — — 磷素 — — 是外膜的主要成分。 为什么?

Lipids
::唇唇

Lipids are that contain mainly carbon, hydrogen, and oxygen. They include substances such as fats and oils, as well as waxes, sterols, some vitamins (A, D, E and K) and phospholipids. Lipid molecules consist of fatty acids , with or without additional molecules. Fatty acids are organic compounds that have the general formula CH ₃ (CH ₂ ) _n COOH, where n usually ranges from 2 to 28 and is always an even number.
::利皮主要是碳、氢和氧,包括脂肪和油、蜡、无毒剂、一些维他命(A、D、E和K)和磷片等物质。利皮分子由脂肪酸组成,有的含有或不含有其他分子。脂肪酸是有机化合物,具有普通的CH3(CH2)nCOOH公式,通常介于2至28之间,始终是偶数。

A distinguishing feature of lipids is that they are insoluble in water. The main biological functions of lipids include energy storage, as the major structural component of , and as important signaling molecules.
::脂肪的一个显著特征是,在水中是无法溶解的,脂肪的主要生物功能包括能源储存,作为...的主要结构成分,以及作为重要的信号分子。

Saturated and Unsaturated Fatty Acids
::饱和和和不饱和脂肪酸

Fatty acids can be saturated or unsaturated. The term saturated refers to the placement of hydrogen atoms around the carbon atoms. In a saturated fatty acid , all the carbon atoms (other than the carbon in the -COOH group) are bonded to as many hydrogen atoms as possible (usually two hydrogens). Saturated fatty acids do not contain any other groups except the -COOH. This is why they form straight chains, as shown in Figure . Because of this structure, saturated fatty acids can be packed together very tightly. This allows organisms to store chemical energy very densely. The fatty tissues of contain mainly saturated fatty acids.
::脂肪酸可以是饱和或不饱和的。 饱和一词指氢原子在碳原子周围的位置。 在饱和脂肪酸中,所有碳原子(非碳-COOH组)都与尽可能多的氢原子(通常为两个氢)相连。饱和脂肪酸除 -COOH外不包含任何其他组别。这就是为什么它们形成直链的原因,如图所示。由于这种结构,饱和脂肪酸可以非常紧紧地组合在一起。这使得生物能够非常密集地储存化学能量。其中的脂肪组织主要是饱和脂肪酸。

In an unsaturated fatty acid , some carbon atoms are not bonded to the maximum number of hydrogen atoms. This is because they are bonded to one or more additional groups, including double and triple bonds between carbons. Wherever these other groups bind with carbon, they cause the chain to bend - they do not form straight chains ( Figure ). This gives unsaturated fatty acids different properties than saturated fatty acids. For example, unsaturated fatty acids are liquids at room temperature whereas saturated fatty acids are solids. Unsaturated fatty acids are found mainly in plants, especially in fatty tissues such as nuts and seeds .
::在不饱和脂肪酸中,一些碳原子没有与最大数量氢原子相连接。 这是因为碳原子被绑在一种或多种额外的组子上, 包括碳之间的双倍和三倍结合。 无论这些其他组群与碳结合, 它们都会导致链条弯曲 — — 它们不形成直线链( 图表 ) 。 这使得不饱和脂肪酸的特性不同于饱和脂肪酸。 例如, 不饱和脂肪酸在室温下是液体,而饱和脂肪酸则是固体。 不饱和脂肪酸主要存在于植物中, 特别是在坚果和种子等脂肪组织中。

Unsaturated fatty acids occur naturally in the bent shapes shown in Figure . However, unsaturated fatty acids can be artificially manufactured to have straight chains like saturated fatty acids. Called trans fatty acids , these synthetic lipids were commonly added to foods until it was found that they increased the risk for certain health problems. Many food manufacturers no longer use trans fatty acids for this reason.
::不饱和脂肪酸自然出现在图中所示的弯曲形状中。然而,不饱和脂肪酸可以人工制造,制造成直链,如饱和脂肪酸。所谓的跨脂肪酸,这些合成脂脂通常添加到食物中,直到发现它们增加了某些健康问题的风险。许多食品制造商因此不再使用反脂肪酸。

Types of Lipids
::利皮类型

Lipids may consist of fatty acids alone or in combination with other compounds. Several types of lipids consist of fatty acids combined with a molecule of alcohol:
::脂酸可能单独或与其他化合物结合而含有脂肪酸。

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• Triglycerides are the main form of stored energy in animals. This type of lipid is commonly called fat. Triglycerides are composed of a glycerol and three fatty acid chains. An example is shown in Figure . In humans, triglycerides are a mechanism for storing unused calories , and their high concentration in correlates with the consumption of excess starches and other carbohydrate-rich foods.
  ::3,3,3,3,3,3,3,2,3,3,3,3,3,2,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,4,3,3,4,4,4,6,6,6,6,6,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7
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• Phospholipids are a major component of the membranes surrounding the cells of all organisms, as they have the ability to form bilayers. The structure of the phospholipid molecule consists of two hydrophobic tails (a diglyceride made of two fatty acid chains) and a hydrophilic head (a phosphate group, PO ₄ ^3- ).
  ::磷脂是所有生物细胞周围膜的主要成分,因为它们能够形成双层细胞,磷素分子的结构包括两个疏水尾(由两条脂肪酸链制成的挖石)和一个水利头(磷酸盐类,PO43-)。
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• Steroids (or sterols) have several functions. Sterols are a subgroup of steroids. The sterol cholesterol is an important part of cell membranes and plays other vital roles in the body. Cholesterol is a precursor to fat-soluble vitamins and steroid hormones . Steroid hormones include the male and female sex hormones . Sterols also have roles as second messengers in signalling pathways.
  ::类固醇(或杀虫醇)具有多种功能。 类固醇是类固醇的一个子组。 胆固醇是细胞膜中的一个重要部分,在体内发挥着其他关键作用。 胆固醇是脂肪溶解维生素和类固醇的前体。 类固醇激素包括男性和女性的性激素。 Sterol胆固醇也是信号路径中的第二使者。

Lipids and Diet
::嘴唇和饮食

Humans need lipids for many vital functions such as storing energy and forming cell membranes. Lipids can also supply cells with energy. In fact, a gram of lipids supplies more than twice as much energy as a gram of or . Lipids are necessary in the diet for most of these functions. Although the can manufacture most of the lipids it needs, there are others, called essential fatty acids , that must be consumed in food. Essential fatty acids include omega-3 and omega-6 fatty acids. Both of these fatty acids are needed for important biological processes, not just for energy.
::人类需要脂质,例如储存能量和形成细胞膜等许多关键功能。利皮也可以用能量供应细胞。事实上,一克脂质的能量比一克或一克多一倍以上。大部分这些功能的饮食都需要脂质。尽管大部分脂质可以制造,但还有一些,称为基本脂肪酸的脂肪酸,必须用在食物中。基本脂肪酸包括 omega-3 和 omega-6 脂肪酸。这两种脂肪酸都是重要的生物过程所需要的,而不仅仅是能源。

Although some lipids in the diet are essential, excess dietary lipids can be harmful. Because lipids are very high in energy, eating too many may lead to unhealthy weight gain. A high-fat diet may also increase lipid levels in the blood. This, in turn, can increase the risk for health problems such as . The dietary lipids of most concern are saturated fatty acids, trans fats, and cholesterol. For example, cholesterol is the lipid mainly responsible for narrowing arteries and causing the disease atherosclerosis .
::尽管饮食中的某些脂质是必需的,但过多的饮食脂质可能是有害的,因为脂质在能量中非常高,吃太多可能导致不健康的体重增加。高脂肪饮食也会增加血液中的脂质水平。这反过来又会增加健康问题的风险。最令人关切的是饱和脂肪酸、跨脂肪和胆固醇。例如,胆固醇是导致动脉缩小和导致疾病塞罗斯硬化的脂肪。

Summary
::摘要

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• Lipids are organic compounds that consist of carbon, hydrogen, and oxygen.
  ::利皮是由碳、氢和氧组成的有机化合物。
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• Lipids are made up of fatty acids and other compounds.
  ::利皮由脂肪酸和其他化合物组成。
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• Lipids provide cells with energy, store energy, and help form cell membranes.
  ::唇膜为细胞提供能量、储存能量和帮助形成细胞膜。

Review
::回顾

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1. What are lipids? Give examples of lipids?
   ::脂质是什么?
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2. Why do molecules of saturated and unsaturated fatty acids have different shapes?
   ::为什么饱和和和不饱和脂肪酸的分子有不同的形状?
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3. Describe the structure and role of phospholipids.
   ::描述磷素的结构和作用。
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4. What type of organic compound is represented by the formula CH ₃ (CH ₂ ) ₄ COOH? How do you know?
   ::公式CH3(CH2)4COOH代表哪一种有机化合物? 你怎么知道?
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5. What are essential fatty acids?
   ::什么是基本脂肪酸?