Name: lipids, fats, and cell membranes
Uploaded: 2020-09-24T15:06:53.000Z
Duration: 3 min 38 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-6

Structure of Lipids

Os lipídios são um grupo de moléculas hidrofóbicas que incluem triglicerídeos, que são utilizados para armazenar energia, e fosfolipídios, que são os principais componentes estruturais das membranas celulares. Os triglicerídeos e a maioria dos fosfolipídios consiste em glicerol e cadeias de ácidos gordos. Os ácidos gordos têm grupos de metilo numa extremidade da cadeia e grupos carboxílicos no extremo oposto.O carbono ligado ao grupo carboxil é chamado de carbono alfa, e o grupo metilo carbono é conhecido como o carbono ómega. Os ácidos gordos variam em comprimento e na presença de ligações duplas na cadeia de hidrocarboneto. Aqueles com ligações duplas são ácidos gordos insaturados e aqueles com apenas uma ligação são ácidos gordos saturados porque estão saturados com um maior número de átomos de hidrogênio possível.Os ácidos gordos frequentemente têm nomes comuns mas podem ser sistematicamente nomeados de acordo com o número de átomos de carbono e o número e posição das ligações duplas na cadeia do carbono. Existem vários métodos de numeração. A referenciação do sistema carboxil conta a posição de todas as ligações duplas do carbono carboxílico, que é numerada como 1.O sistema de referenciamento ómega conta a posição da dupla ligação mais próxima para o carbono ómega, com o ómega de carbono numerada como 1. Por exemplo, o ácido linolênico, um ácido ómega 3-gorduroso, tem 18 carbonos e obrigações duplas nas posições 9, 12, e 15 da contagem da extremidade carboxil. Isto será chamado 18:3 Δ9, 12, 15 de acordo com o sistema carboxil de referenciamento e 18:3 de acordo com o sistema ómega de referenciamento.Os ácidos gordos insaturados podem ocorrem em duas configurações:cis e trans. Na configuração cis, os hidrogénios sobre os carbonos envolvidos na dupla ligação estão no mesmo lado da ligação, enquanto na configuração trans, os hidrogênios estão localizados no lado oposto. Estruturalmente, os ácidos gordos cis têm correntes dobradas, enquanto que os ácidos gordos trans têm correntes retas.O consumo de gorduras trans tem sido considerado responsável por diversos tratamentos de doenças cardiovasculares, enquanto que o consumo de ácidos gordos cis, tais como omega-3 e omega-6, são conhecidos por serem benéficos para a saúde. Os triglicerídeos, vulgarmente conhecidas como gorduras, são utilizados principalmente para o armazenamento de energia. São compostos por três ácidos gordos ligados ao glicerol através de ligações ésteres entre a extremidade hidroxila do glicerol e as extremidades carboxílicas dos ácidos gordos resultantes na formação de uma molécula não-polar.Se todos os três ácidos gordos forem do mesmo tipo, são conhecidos como triglicerídeos simples. Se os três ácidos gordos diferirem, eles são conhecidos como triglicerídeos mistos. Outro tipo de lipídicos, fosfolipídios, é um importante característica estrutural das membranas biológicas.Têm cabeças hidrofílicas que consistem em grupos de fosfatos modificados com um grupo de álcool hidrofílico e caudas hidrofóbicas de ácidos gordos. A composição destas cabeças e caudas pode variar, resultando em diferentes tipos de lipídios da membrana. Os glicerofosfolípidos são um tipo comum de fosfolipídio que consiste em dois ácidos gordos e um grupo altamente polar anexados a cada carbono de glicerol através de ligações de éster e fosfodiesterase, respetivamente.

estrutura dos lípidos

Os lípidos incluem um grupo diverso de compostos que são amplamente não polares na natureza. Isto porque são hidrocarbonetos que incluem principalmente ligações carbono-carbono ou carbono-hidrogénio não polares. As moléculas não polares são hidrofóbicas (“temem a água”), ou insolúveis em água. Os lípidos executam muitas funções diferentes em uma célula. As células armazenam energia para o uso a longo prazo na forma de gorduras. Os lípidos também fornecem isolamento do meio ambiente para plantas e animais. Por exemplo, ajudam a manter as aves e mamíferos aquáticos secos ao formar uma camada protetora sobre peles ou penas devido à sua natureza hidrofóbica repelente de água. Os lípidos são também os blocos de construção de muitas hormonas e são um constituinte importante de todas as membranas celulares. Os lípidos incluem gorduras, óleos, ceras, fosfolípidos, e esteróides.
Estrutura Geral dos Lípidos
Uma molécula de gordura consiste em dois componentes principais—glicerol e ácidos gordos. O glicerol é um composto orgânico (álcool) com três carbonos, cinco hidrogénios, e três grupos hidroxilo (OH). Os ácidos gordos têm uma longa cadeia de hidrocarbonetos à qual está ligado um grupo carboxilo, daí o nome de “ácido gordo”. O número de carbonos nos ácidos gordos pode variar de 4 a 36. Os mais comuns são aqueles que contêm 12–18 carbonos. Em uma molécula de gordura, os ácidos gordos unem-se a cada um dos três carbonos da molécula de glicerol com uma ligação éster através de um átomo de oxigénio. A junção de três ácidos gordos a um esqueleto de glicerol em uma reação de desidratação forma triacilglicerol. Os três ácidos gordos do triacilglicerol podem ser semelhantes ou diferentes.
Um fosfolípido é outro tipo comum de lípido. É uma molécula anfipática, o que significa que tem uma parte hidrofóbica e uma hidrofílica. As cadeias de ácidos gordos são hidrofóbicas e não podem interagir com a água; enquanto isso, o grupo que contém fosfato é hidrofílico e interage com a água. Os grupos hidrofílicos da cabeça dos fosfolípidos estão voltados para a solução aquosa. As caudas hidrofóbicas estão sequestradas no meio da bicamada.
Ácidos Gordos
Os ácidos gordos podem ser saturados ou insaturados. Em uma cadeia de ácidos gordos, se houver apenas ligações simples entre os carbonos vizinhos na cadeia de hidrocarbonetos, o ácido gordo é saturado. O ácido esteárico é um exemplo de um ácido gordo saturado.
Quando a cadeia de hidrocarbonetos contém uma ligação dupla, o ácido gordo é insaturado. O ácido oleico é um exemplo de um ácido gordo insaturado. A maioria das gorduras insaturadas são líquidas à temperatura ambiente e são chamadas de óleos. Se houver uma ligação dupla na molécula, então é uma gordura monoinsaturada (por exemplo, azeite), e se houver mais de uma ligação dupla, então é uma gordura poliinsaturada (por exemplo, óleo de canola). Ácidos gordos rectos longos com ligações simples geralmente compactam-se firmemente e são sólidos à temperatura ambiente. Gorduras animais com ácido esteárico e ácido palmítico (comuns na carne) e a gordura com ácido butírico (comum na manteiga) são exemplos de gorduras saturadas.
Os ácidos gordos podem ser adicionalmente classificados em cis e trans. Cis e trans indicam a configuração da molécula em torno da ligação dupla. Se os hidrogénios estiverem presentes no mesmo plano, é uma gordura cis. Se os átomos de hidrogénio estiverem em dois planos diferentes, trata-se de uma gordura trans. A ligação dupla cis causa uma dobra ou “torção” que impede que os ácidos gordos se compactem firmemente, mantendo-os líquidos à temperatura ambiente. Azeite, óleo de milho, óleo de canola, e óleo de fígado de bacalhau são exemplos de gorduras insaturadas. As gorduras insaturadas ajudam a diminuir os níveis de colesterol no sangue; enquanto isso, as gorduras saturadas contribuem para a formação de placas nas artérias.
Gorduras Trans
A indústria alimentar hidrogena artificialmente os óleos para torná-los semi-sólidos e de uma consistência desejável para muitos produtos alimentares processados. Durante este processo, as ligações duplas da conformação cis– na cadeia de hidrocarbonetos podem converter-se em ligações duplas em conformação trans–.
Margarina, alguns tipos de manteiga de amendoim, e gordura alimentar são exemplos de gorduras trans hidrogenadas artificialmente. Estudos recentes demonstraram que um aumento de gorduras trans na dieta humana pode levar a níveis mais elevados de lipoproteínas de baixa densidade (LDL), ou colesterol “mau”, o que, por sua vez, pode levar à deposição de placas nas artérias, resultando em doença cardíaca.
Ácidos Gordos Ómega
Os ácidos gordos essenciais são aqueles que o corpo humano precisa mas não sintetiza. Consequentemente, eles têm de ser suplementados por ingestão através da dieta. Os ácidos gordos ómega-3 caem nesta categoria e são um de apenas dois conhecidos pelos humanos (o outro é o ácido gordo ómega-6). Estes são ácidos gordos poliinsaturados e são ómega-3 porque uma ligação dupla liga o terceiro carbono do final da cadeia de hidrocarbonetos ao seu carbono vizinho.
O ácido alfa-linolénico é um exemplo de um ácido gordo ómega-3. Tem três ligações duplas cis e, como resultado, uma forma curva. O salmão, a truta, e o atum são fontes boas de ácidos gordos ómega-3. Estudos indicam que os ácidos gordos ómega-3 reduzem o risco de morte súbita devido a ataques cardíacos, baixam os triglicerídeos no sangue, diminuem a pressão arterial, e previnem a trombose ao inibir a coagulação sanguínea. Eles também reduzem a inflamação e podem ajudar a reduzir o risco de alguns cancros em animais.
Este texto é adaptado de <a href="https://openstax.org/books/biology-2e/pages/3-3-lipids">Openstax, Biology 2e, Chapter 3.3: Lipids</a>.

Estrutura dos Lípidos

Os lipídios incluem um grupo diversificado de compostos que são em grande parte de natureza apolar. Isso ocorre porque são hidrocarbonetos que incluem principalmente ...

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KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

lipids, fats, and cell membranes

Lipids are nonpolar molecules that do not mix well with water. They are hydrophobic, which means “water fearing,” because they contain mostly nonpolar carbon-carbon and carbon-hydrogen bonds. In cells, lipids store long-term energy as fats, help insulate plants and animals, and form protective water-repellent layers on feathers and fur. They are also part of cell membranes and serve as building blocks for many hormones. Common lipids include fats, oils, waxes, phospholipids, and steroids.

A fat molecule is built from glycerol and fatty acids. Glycerol is an alcohol with three carbons, five hydrogens, and three hydroxyl groups. Fatty acids have a long hydrocarbon chain with a carboxyl group attached. Their chains can range from 4 to 36 carbons, but 12 to 18 carbons is most common. In a fat, three fatty acids join to one glycerol backbone through ester bonds in a dehydration reaction. This forms a triacylglycerol. The three fatty acids may be the same or different.

Phospholipids are another major lipid type. They are amphipathic, which means they have both a hydrophobic part and a hydrophilic part. The fatty acid tails repel water, while the phosphate-containing head attracts water. In water, the heads face outward toward the solution and the tails gather in the middle of the bilayer.

Fatty acids can be saturated or unsaturated. Saturated fatty acids have only single bonds between carbon atoms. Stearic acid is one example. Unsaturated fatty acids contain one or more double bonds. Oleic acid is an example, and most unsaturated fats are liquid at room temperature and are called oils. Monounsaturated fats, such as olive oil, have one double bond. Polyunsaturated fats, such as canola oil, have more than one. Straight saturated fatty acids pack tightly, so they are usually solid at room temperature. Animal fats with stearic acid and palmitic acid, as well as butter with butyric acid, are examples.

Unsaturated fatty acids can also be cis or trans. These terms describe the arrangement around a double bond. In cis fats, the hydrogens are on the same plane. In trans fats, they are on different planes. The cis double bond creates a kink that prevents tight packing, which helps keep the fat liquid. Olive oil, corn oil, canola oil, and cod liver oil are examples of unsaturated fats. Unsaturated fats tend to lower blood cholesterol levels, while saturated fats can contribute to plaque formation in arteries.

Trans fats are often made by hydrogenating oils to make them more semi-solid for processed foods. During this process, some cis double bonds can change to trans double bonds. Margarine, some peanut butter, and shortening are examples of artificially hydrogenated trans fats. Studies show that more trans fats in the diet can raise low-density lipoproteins, or LDL, the “bad” cholesterol. This can increase plaque buildup in arteries and raise the risk of heart disease.

Omega-3 fatty acids are essential fatty acids, which means the body needs them but does not make them. They must come from the diet. Omega-3s are one of only two known essential fatty acid groups for humans, along with omega-6 fatty acids. They are polyunsaturated, and the name omega-3 means the third carbon from the end is part of a double bond. Alpha-linolenic acid is an example. It has three cis double bonds and a curved shape. Salmon, trout, and tuna are good sources. Research suggests omega-3 fatty acids can reduce the risk of sudden death from heart attacks, lower blood triglycerides, decrease blood pressure, prevent blood clotting, and reduce inflammation. They may also help lower the risk of some cancers in animals.

Lipids, Fats, and Cell Membranes

functional groups

Functional Groups in Organic Chemistry

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structure of lipids

Lipids are nonpolar molecules that do not mix well with water. They are hydrophobic, which means “water fearing,” because they contain mostly nonpolar carbon-carbon and carbon-hydrogen bonds. In cells, lipids store long-term energy as fats, help insulate plants and animals, and form protective water-repellent layers on feathers and fur. They are also part of cell membranes and serve as building blocks for many hormones. Common lipids include fats, oils, waxes, phospholipids, and steroids. A...

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key terms and concepts

Explore how lipids store energy, build cell membranes, and differ as saturated, unsaturated, trans, and omega-3 fats in high school biology.

Lipids, Fats, and Cell Membranes | JoVE K12

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Breathing

The process of breathing, inhaling and exhaling, involves the coordinated movement of the chest wall, the lungs, and the muscles that move them. Two ...

Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.] [Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.]

HS-LS1-2

What is Homeostasis?

Maintaining homeostasis requires that the body continuously maintain its internal conditions. Each physiological condition has a particular set point, ...

Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis. [Clarification Statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.] [Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.]

HS-LS1-3

Lipids, Fats, and Cell Membranes

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