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    Yum!
    ::优美!

    It glistens with fat, from the cheese to the steak. You may never have visited Philadelphia, but you probably know about its famous gastronomic delight... the Philly cheesesteak. Both cheese and steak are typically high-fat foods, so this sandwich is definitely not recommended if you are following a low-fat diet. We need some fats in our diet for good health, but too much of a good thing can be harmful to our health, no matter how delicious  it tastes. What are fats? And why do we have such a love-hate relationship with them? Read on to find out.
    ::从奶酪到牛排都有脂肪的味道。你可能从未去过费城,但你可能知道它有名的胃力组乐...菲利士奶酪牛排。奶酪和牛排一般都是高脂肪食品,所以如果你是低脂肪饮食的话,这个三明治绝对不推荐。我们需要一些脂肪来维持健康,但是太多的好东西会伤害我们的健康,不管它多美味。什么是脂肪?为什么我们和它们有着如此深爱的感情关系?你看看吧。

    Lipids and Fatty Acids 
    ::利皮和脂肪酸

    Fats are actually a type of lipid. Lipids  are a major class of biochemical compounds that includes oils, as well as fats. Among other things, organisms use lipids to store energy .
    ::脂肪实际上是一种脂质。 脂质是一种主要的生化化合物,包括油和脂肪。 除其他外,生物利用脂质储存能量。

    Lipid molecules consist mainly of repeating units called fatty acids . There are two types of fatty acids: saturated fatty acids and unsaturated fatty acids . Both types consist mainly of simple chains of carbon atoms bonded to one another and to hydrogen atoms. The two types of fatty acids differ in how many hydrogen atoms they contain  and the number of  bonds between carbon atoms.
    ::利皮分子主要包括称为脂肪酸的重复单位,有两种脂肪酸:饱和脂肪酸和不饱和脂肪酸,两种主要包括简单的碳原子链和氢原子。两种脂肪酸在所含氢原子的数量和碳原子之间的联结数量上有所不同。

    Saturated Fatty Acids
    ::饱饱和脂肪酸

    In saturated fatty acids , carbon atoms are bonded to as many hydrogen atoms as possible. All the carbon-to-carbon atoms share just single bonds between them. This causes the molecules to form straight chains, as shown in the figure . The straight chains can be packed together very tightly, allowing them to store energy in a compact form. Saturated fatty acids have relatively high melting points, which explains  why they are solids at room temperature. use saturated fatty acids to store energy.
    ::在饱和脂肪酸中,碳原子与尽可能多的氢原子捆绑在一起。所有碳-碳原子在它们之间共享单一的链条。这导致分子形成直链,如图所示。直链可以非常紧紧地包装在一起,允许它们以紧凑的形式储存能量。饱和脂肪酸的熔点相对较高,这解释了为什么它们在室温下是固态的。使用饱和脂肪酸储存能量。

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    Fatty Acids. Saturated fatty acids have straight chains, like the three fatty acids shown on the left. Unsaturated fatty acids have bent chains, like all the other fatty acids in the figure.
    ::脂肪酸。饱和脂肪酸有直链,像左边显示的三个脂肪酸一样。不饱和脂肪酸有弯曲链,像图中所有其他脂肪酸一样。

    Unsaturated Fatty Acids
    ::不饱和脂肪酸

    In unsaturated fatty acids , some carbon atoms are not bonded to as many hydrogen atoms as possible. Instead, they form double or even triple bonds with other carbon atoms. This causes the chains to bend (see the figure ). The bent chains cannot be packed together very tightly. Unsaturated fatty acids have relatively low melting points, which explains why they are liquids at room temperature. Plants use unsaturated fatty acids to store energy.
    ::在不饱和脂肪酸中,一些碳原子没有与尽可能多的氢原子结合。相反,它们与其他碳原子形成双倍甚至三倍的联结。这导致链条弯曲(见图 ) 。 弯曲的链条无法非常紧紧地包装在一起。 不饱和脂肪酸的熔点相对较低,这解释了为什么它们是室内温度下的液体。植物用不饱和脂肪酸储存能量。

    Monounsaturated fatty acids contain one less hydrogen atom than the same-length saturated fatty acid chain. Monounsaturated fatty acids are liquids at room temperature, but start to solidify at refrigerator temperatures. Good food sources of monounsaturated fats include olive oils,  peanut oils, and avocados.
    ::单饱和脂肪酸所含氢原子比同长饱和脂肪酸链所含氢原子少一个。 单饱和脂肪酸是室温时的液体,但在冰箱温度下开始固化。 单饱和脂肪的好食物来源包括橄榄油、花生油和鳄梨。

    Polyunsaturated fatty acids contain at least two fewer hydrogen atoms than the same-length saturated fatty acid chain. Polyunsaturated fatty acids are liquids at room temperature and remain in the liquid state in the refrigerator. Good food sources of polyunsaturated fats include  safflower oils, soybean oils, and many nuts and seeds .
    ::聚饱和脂肪酸所含氢原子至少比同长饱和脂肪酸链少两个。 多饱和脂肪酸是室温下的液体,在冰箱中仍处于液体状态。 多饱和脂肪的好食物来源包括红花油、大豆油以及许多坚果和种子。

    Types of Lipids
    ::利皮类型

    Lipids may consist of fatty acids alone, or they may contain other chemical components,  as well. For example, some lipids contain alcohol or phosphate groups. Types of lipids include triglycerides, phospholipids, and steroids. Each type has different functions in living things.
    ::例如,有些脂质含有酒精或磷酸类,各种脂类包括三甘酸酯、磷素和类固醇,每种脂类在生物中都有不同的功能。

    Triglycerides
    ::三甘烯酸酯

    Triglycerides are formed by combining a molecule of glycerol with three fatty acid molecules , as shown . Glycerol (also called glycerine) is a simple compound known as a sugar alcohol. It is a colorless, odorless liquid that is sweet tasting and nontoxic. Triglycerides are the main constituent of body fat in humans and other animals. They are also found in fats derived from plants. There are many different types of triglycerides, with the main division being between those that contain saturated fatty acids and those that contain unsaturated fatty acids.
    ::甘油(又称甘油)是一种称为糖酒精的简单化合物,是一种无色、无味的液体,具有甜味和无毒性,三甘油是人体和其他动物体内脂肪的主要成分,在植物产生的脂肪中也发现了三甘油。有多种不同的三甘油,主要区别在于含有饱和脂肪酸的化合物和含有不饱和脂肪酸的化合物。

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    In the human bloodstream, triglycerides play an important role in metabolism as energy sources and transporters of dietary fat. They contain more than twice as much energy as , the other major source of energy in the diet. When you eat, your body converts any calories it doesn't need to use right away into triglycerides, which are stored in your fat . When you need energy between meals, trigger the release of some of these stored triglycerides back into the bloodstream.
    ::在人类血液中,三甘酸盐在新陈代谢中起着重要作用,作为能源来源和饮食脂肪的运输者。它们含有的能量是饮食中另一种主要能源的两倍以上。当您吃东西时,身体将任何热量转换成三甘酸酯,而这种热量则储存在脂肪中。当您需要进食之间的能量时,触发将其中一些储存的三甘酸盐释放回血液中。

    Phospholipids
    ::磷脂

    Phospholipids   are a major component of the of all living things. Each phospholipid molecule has a "tail" consisting of two long fatty acids, and a "head" consisting of a phosphate group and glycerol molecule (see diagram ). The phosphate group is a small, negatively-charged molecule. The phospholipid head is hydrophilic , or attracted to . The fatty acid tail of the phospholipid is hydrophobic , or repelled by water. These properties allow phospholipids to form a two-layered cell membrane, which is also called a bilayer.
    ::磷素是所有生物物质的主要成分。每种磷素分子都有由两个长长脂肪酸组成的“尾部”和由磷酸类和甘油分子组成的“头部”(见图 ) 。磷酸盐类是一个微小的负电荷分子,磷素头具有水利作用,或被吸引到。磷素的脂肪酸尾巴具有疏水性,或被水排出。这些特性允许磷素形成一种双层细胞膜,也称为双层膜。

    As shown in the diagram , a forms when many phospholipid molecules line up tail to tail, forming an inner and outer surface of hydrophilic heads. The hydrophyilic heads point toward both the watery extracellular space and the watery inside space (lumen) of the cell.
    ::如图所示,许多磷素分子从尾部到尾部排列在一起,形成一个水益头的内表和外表。 水益头指向细胞的水外细胞空间和水内空间(lumen)。

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    Cell membranes consist of a double layer of phospholipid molecules.
    ::细胞膜由一层双层磷素分子组成。

    Steroids
    ::类固醇

    Steroids   are lipids with a ring structure. Each steroid has a core of 17  carbon atoms, which are arranged in four rings of five or six carbons each (see model pictured ). Steroids vary by the other components attached to this four-ring core. Hundreds of steroids are found in plants, animals, and , but most steroids have one of just two principal biological functions. Some steroids (such as cholesterol) are important components of cell membranes, while many other steroids are hormones, which are messenger molecules. In humans, steroid hormones include cortisone — a fight-or- flight hormone — and the sex hormones estrogen and testosterone .  
    ::类固醇是带有环状结构的脂质,每类类类固醇的核心为17个碳原子,每类碳原子由4个环组成,每类碳原子由5或6个碳组成(见模型图)。类固醇随四环核的其他成分而异。在植物、动物和类固醇中发现了数百种类固醇,但大多数类固醇只有两种主要生物功能之一。一些类固醇(如胆固醇)是细胞膜的重要成分,而许多其他类固醇则是激素,它们是信使分子。在人类中,类固醇激素包括可激素 — 一种战斗或飞行激素 — 以及性激素、雌激素和睾酮。

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    Each steroid molecule consists of a four-ring core of 17 carbon atoms (black balls in the model). The other components of the molecule may vary and determine the steroid's function.
    ::每个类固醇分子由一个由17个碳原子(模型中的黑球)组成的四环核心组成。分子的其他成分可能不同,决定类固醇的功能。

    Feature: My Human Body
    ::特质:我的人体

    During a routine checkup with your family doctor, your was collected for a lipid profile. The results are back, and your triglyceride level is 180 mg/dL. Your doctor says this is a little high. A blood triglyceride level of 150 mg/dL or lower is considered normal. Higher levels of triglycerides in the blood have been linked to an increased risk of atherosclerosis , heart disease, and stroke . 
    ::在与您的家庭医生进行例行检查期间,您是按脂质特征采集的。结果出来了,您的三重血压水平为180毫克/dL。您的医生说这有点高。血液三重血压水平为150毫克/dL或低于150毫克/dL或低于150毫克/dL,这被认为是正常的。血液中的三重血糖化物水平的提高与神经硬化、心脏病和中风的风险增加有关。

    If a blood test reveals that you have high triglycerides, the levels can be lowered through healthy lifestyle choices and/or prescription medications. Healthy lifestyle choices to control triglyceride levels include:
    ::如果血液检测发现你患有高三甘酸酯,通过健康的生活方式选择和/或处方药物,可以降低该水平。

    • Weight loss:  If you are overweight, losing even 5 or 10 pounds may help lower your triglyceride level.
      ::体重损失:如果体重超重,甚至损失5或10磅,可能有助于降低三重水位水平。
    • Calorie reduction:  Extra calories are converted to triglycerides and stored as fat, so reducing your calories should also reduce your triglyceride level.
      ::减少卡路里热量:将额外卡路里转换成三甘酸盐,作为脂肪储存,因此降低卡路里热量,也会降低你的三甘酸盐水平。
    • Reduction in sugars and refined foods:  Simple carbohydrates, such as sugars and foods made with white flour, can increase triglyceride levels.
      ::减少糖和精炼食品:简单的碳水化合物,如糖和用白面粉制成的食品,可提高三重水合物水平。
    • Healthier fats:  Trade saturated fats found in animal foods for healthier unsaturated fats found in plants and oily . For example, substitute olive oil for butter and salmon for red meat.
      ::更健康的脂肪:在动物食品中发现的贸易饱和脂肪,用于植物和油脂中发现的更健康的不饱和脂肪。例如,用橄榄油代替黄油,用鲑鱼代替红肉。
    • Cut back on alcohol:  Alcohol is high in calories and sugar. It has a strong effect on triglyceride levels.
      ::减少酒精:酒精在卡路里和糖中含量较高,对三重冰酸水平有强烈影响。
    • Regular :  Aim for at least 30 minutes of physical activity on most or all days of the week.
      ::经常:在一周的大部分或所有天数上,至少要进行30分钟的体育活动。

    If healthy lifestyle changes aren't enough to bring down high triglyceride levels, drugs prescribed by your doctor are likely to help.
    ::如果健康生活方式的改变不足以降低高三重血压水平,那么医生开出的药物可能会有帮助。

    Summary
    ::摘要

    • Lipids are a major class of biochemical compounds that includes oils and fats. Organisms use lipids for storing energy and for making cell membranes and hormones, which are chemical messengers.
      ::利皮是一种主要的生化化合物,包括油和脂肪。 生物利用脂质储存能量,制造细胞膜和荷尔蒙,作为化学信使。
    • Lipid molecules consist mainly of repeating units called fatty acids. D epending on the proportion of hydrogen atoms they contain, f atty acids may be saturated or unsaturated. Animals store fat as saturated fatty acids, while plants store fat as unsaturated fatty acids.
      ::碱性分子主要包括称为脂肪酸的重复单位,根据含氢原子的比例,脂肪酸可以饱和或不饱和,动物将脂肪作为饱和脂肪酸储存,植物将脂肪作为不饱和脂肪酸储存。
    • Types of lipids include triglycerides, phospholipids, and steroids. Each type consists of fatty acids and certain other molecules. Each also has different functions.
      ::脂类包括三甘酸酯、磷素和类固醇,每种由脂肪酸和某些其他分子组成,各有不同的功能。
    • Triglycerides contain glycerol (an alcohol), in addition to fatty acids. Humans and other animals store fat as triglycerides in fat cells.
      ::人类和其他动物在脂肪细胞中将脂肪作为三甘化物储存在三甘化物中。
    • In addition to fatty acids, phospholipids contain phosphate and glycerol. They are the main component of cell membranes in all living things.
      ::除脂肪酸外,磷素还含有磷酸盐和甘油醇,是细胞膜在所有生物物质中的主要成分。
    • Steroids are lipids with a four-ring structure. Some steroids (such as cholesterol) are important components of cell membranes. Many other steroids are hormones. An example of a human hormone is cortisone, which is the fight-or-flight hormone.
      ::类固醇是四环结构的脂质。有些类固醇(如胆固醇)是细胞膜的重要成分。其他许多类固醇是荷尔蒙。人类荷尔蒙的一个例子是气质松,即战斗或飞行荷尔蒙。

    Review
    ::回顾

    1. What are lipids?
    ::1. 什么是脂质?

    2. Compare and contrast saturated and unsaturated fatty acids.
    ::2. 比较和对比饱和和不饱和脂肪酸。

    3. Identify three major types of lipids. Describe differences in their structures.
    ::3. 查明三种主要的脂类:说明其结构的差异。

    4. How do triglycerides play an important role in human metabolism?
    ::4. 三甘酸酯如何在人类新陈代谢中发挥重要作用?

    5. Explain how phospholipids form cell membranes.
    ::5. 解释磷素如何形成细胞膜。

    6. What is cholesterol? What is its major function?
    ::6. 什么是胆固醇?其主要功能是什么?

    7. Give three examples of steroid hormones in humans.
    ::7. 举三个人类类固醇荷尔蒙的例子。

    8. Which type of fatty acid do you think is predominant in the steak and cheese in the cheesesteak shown above? Explain your answer.
    ::8. 你认为哪类脂肪酸在上述奶酪牛排和奶酪中占主导地位?请解释你的答复。

    9. Which type of fat would be the most likely to stay liquid in colder temperatures: bacon fat, olive oil, or soybean oil? Explain your answer.
    ::9. 哪种脂肪最有可能在较冷的温度下保持液体:培根脂肪、橄榄油或大豆油?

    10. Why do you think that the shape of the different types of fatty acid molecules affects how easily they solidify?
    ::10. 为什么你认为不同类型的脂肪酸分子的形状会影响它们如何容易固化?

    11. High cholesterol levels in the bloodstream can cause negative health effects. Explain why we wouldn’t want to get rid of all of   the cholesterol in our bodies.
    ::11. 血液中的胆固醇含量高可能会对健康产生不利影响。 解释为什么我们不想消除体内的所有胆固醇。

    12. Name two types of lipids that are part of the cell membrane.
    ::12. 列出构成细胞膜一部分的两种脂质。

    13. True or False:  Fatty acids are made up of triglycerides.
    ::13. 真酸或假酸:脂肪酸由三甘酸酯组成。

    14. Which type of lipid often functions as chemical messenger molecules?
    ::14. 哪种脂质通常发挥化学传递分子的作用?

    Explore More
    ::探索更多

    Watch the video below to learn more about  the hormone cortisone. 
    ::观看下面的视频 来了解更多关于荷尔蒙可乐松。

     Watch the video below to learn more about triglycerides and the difference between saturated and unsaturated fatty acids. 
    ::并了解饱和脂肪酸与不饱和脂肪酸之间的区别。