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

Lipide sind eine Gruppe hydrophober Moleküle, zu denen Triglyceride gehören, die zur Energiespeicherung verwendet werden, und Phospholipide, die die Hauptstrukturkomponenten der Zellmembranen sind.
Triglyceride und die meisten Phospholipide bestehen aus Glycerin- und Fettsäureketten.
Fettsäuren haben Methylgruppen an einem Ende der Kette und Carboxylgruppen am anderen Ende. Der Kohlenstoff, der mit der Carboxylgruppe verbunden ist, wird als Alpha-Kohlenstoff bezeichnet, und der Kohlenstoff der Methylgruppe wird als Omega-Kohlenstoff bezeichnet.
Fettsäuren variieren in der Länge und dem Vorhandensein von Doppelbindungen in der Kohlenwasserstoffkette. Diejenigen mit Doppelbindungen sind ungesättigte Fettsäuren und solche mit nur Einfachbindungen sind gesättigte Fettsäuren, weil sie mit der größtmöglichen Anzahl von Wasserstoffatomen gesättigt sind.
Fettsäuren haben oft gebräuchliche Namen, können aber systematisch nach der Anzahl der Kohlenstoffatome und der Anzahl und Position der Doppelbindungen in der Kohlenstoffkette benannt werden.
Es gibt mehrere gängige Nummerierungsmethoden. Das Carboxyl-Referenzierungssystem zählt die Position aller Doppelbindungen vom Carboxylkohlenstoff, der als 1 nummeriert ist. Das Omega-Referenzierungssystem zählt die Position der Doppelbindung, die dem Omega-Kohlenstoff am nächsten liegt, wobei der Omega-Kohlenstoff als 1 nummeriert ist.
Zum Beispiel hat Linolensäure, eine Omega-3-Fettsäure, 18 Kohlenstoffe und Doppelbindungen an den Positionen 9, 12 und 15, gerechnet vom Carboxylende. Dies wird 18:3 Δ9, 12, 15 nach dem Carboxyl-Referenzierungssystem und 18:3 (ω-3) nach dem Omega-Referenzierungssystem genannt.
Ungesättigte Fettsäuren können in zwei Konfigurationen vorkommen: cis und trans. In der cis-Konfiguration befinden sich die Wasserstoffatome an den an der Doppelbindung beteiligten Kohlenstoffen auf der gleichen Seite der Bindung, während sich die Wasserstoffatome in der trans-Konfiguration auf den gegenüberliegenden Seiten befinden. 
Strukturell haben cis-Fettsäuren gebogene Ketten, während trans-Fettsäuren gerade Ketten haben.
Es wurde festgestellt, dass der Verzehr von Transfetten für verschiedene Herz-Kreislauf-Erkrankungen verantwortlich ist, während der Verzehr von cis-Fettsäuren wie Omega-3 und Omega-6 als gesundheitsfördernd bekannt ist.
Triglyceride, umgangssprachlich als Fette bekannt, werden in erster Linie zur Speicherung von Energie verwendet. Sie bestehen aus drei Fettsäuren, die durch Esterbindungen zwischen den Hydroxylenden des Glycerins und den Carboxylenden der Fettsäuren mit Glycerin verbunden sind, was zur Bildung eines unpolaren Moleküls führt.
Wenn alle drei Fettsäuren vom gleichen Typ sind, werden sie als einfache Triglyceride bezeichnet. Unterscheiden sich die drei Fettsäuren, spricht man von gemischten Triglyceriden.
Eine andere Art von Lipiden, die Phospholipide, ist ein wichtiges strukturelles Merkmal biologischer Membranen.
Sie haben hydrophile Köpfe, die aus Phosphatgruppen bestehen, die mit einer hydrophilen Alkoholgruppe modifiziert sind, und hydrophoben Fettsäureschwänzen. Die Zusammensetzung dieser Köpfe und Schwänze kann variieren, was zu unterschiedlichen Arten von Membranlipiden führt.
Glycerophospholipide sind eine häufige Art von Phospholipiden, die aus zwei Fettsäuren und einer hochpolaren Gruppe bestehen, die an jeden Kohlenstoff des Glycerins durch Ester- bzw. Phosphodiesterbindungen gebunden sind.

struktur von lipiden

Lipide umfassen eine vielfältige Gruppe von Verbindungen, die größtenteils unpolarer Natur sind. Dies liegt daran, dass es sich um Kohlenwasserstoffe handelt, die überwiegend unpolare Kohlenstoff-Kohlenstoff- oder Kohlenstoff-Wasserstoff-Bindungen enthalten. Unpolare Moleküle sind hydrophob („wasserscheu“) oder in Wasser unlöslich. Lipide erfüllen in einer Zelle viele verschiedene Funktionen. Zellen speichern Energie für den Langzeitgebrauch in Form von Fetten. Lipide isolieren Pflanzen und Tiere auch von der Umwelt. Aufgrund ihrer wasserabweisenden hydrophoben Beschaffenheit tragen sie beispielsweise dazu bei, Wasservögel und Säugetiere trocken zu halten, indem sie eine Schutzschicht über Fell oder Federn bilden. Lipide sind außerdem Bausteine vieler Hormone und ein wichtiger Bestandteil aller Zellmembranen. Zu den Lipiden zählen Fette, Öle, Wachse, Phospholipide und Steroide. Allgemeine Struktur von Lipiden Ein Fettmolekül besteht aus zwei Hauptkomponenten – Glycerin und Fettsäuren. Glycerin ist eine organische Verbindung (Alkohol) mit drei Kohlenstoffatomen, fünf Wasserstoffatomen und drei Hydroxylgruppen (OH). Fettsäuren bestehen aus einer langen Kette von Kohlenwasserstoffen, an die eine Carboxylgruppe gebunden ist, daher der Name „Fettsäure“. Die Anzahl der Kohlenstoffe in der Fettsäure kann zwischen 4 und 36 liegen. Am häufigsten sind solche mit 12–18 Kohlenstoffen. In einem Fettmolekül binden die Fettsäuren über ein Sauerstoffatom mit einer Esterbindung an jeden der drei Kohlenstoffatome des Glycerinmoleküls. Durch die Verbindung von drei Fettsäuren mit einem Glyceringerüst in einer Dehydratisierungsreaktion entsteht Triacylglycerin. Die drei Fettsäuren im Triacylglycerin können ähnlich oder unterschiedlich sein. Ein Phospholipid ist ein weiterer häufiger Lipidtyp. Es ist ein amphipathisches Molekül, d. h. es hat einen hydrophoben und einen hydrophilen Teil. Die Fettsäureketten sind hydrophob und können nicht mit Wasser interagieren; die phosphathaltige Gruppe hingegen ist hydrophil und interagiert mit Wasser. Die hydrophilen Kopfgruppen der Phospholipide sind der wässrigen Lösung zugewandt. Die hydrophoben Enden sind in der Mitte der Doppelschicht abgesondert. Fettsäuren Fettsäuren können gesättigt oder ungesättigt sein. Wenn in einer Fettsäurekette nur Einfachbindungen zwischen benachbarten Kohlenstoffatomen in der Kohlenwasserstoffkette vorhanden sind, ist die Fettsäure gesättigt. Stearinsäure ist ein Beispiel für eine gesättigte Fettsäure. Wenn die Kohlenwasserstoffkette eine Doppelbindung enthält, ist die Fettsäure ungesättigt. Ölsäure ist ein Beispiel für eine ungesättigte Fettsäure. Die meisten ungesättigten Fette sind bei Raumtemperatur flüssig und werden Öle genannt. Wenn das Molekül eine Doppelbindung enthält, handelt es sich um ein einfach ungesättigtes Fett (z. B. Olivenöl), und wenn mehr als eine Doppelbindung vorhanden ist, handelt es sich um ein mehrfach ungesättigtes Fett (z. B. Rapsöl). Lange gerade Fettsäuren mit Einfachbindungen liegen im Allgemeinen dicht beieinander und sind bei Raumtemperatur fest. Beispiele für gesättigte Fette sind tierische Fette mit Stearinsäure und Palmitinsäure (häufig in Fleisch) und Fett mit Buttersäure (häufig in Butter). Fettsäuren können zusätzlich in Cis- und Trans-Fettsäuren eingeteilt werden. Cis und trans geben die Konfiguration des Moleküls um die Doppelbindung an. Wenn Wasserstoffe in derselben Ebene vorhanden sind, handelt es sich um ein cis-Fett. Befinden sich die Wasserstoffatome auf zwei verschiedenen Ebenen, handelt es sich um ein Transfett. Die cis-Doppelbindung verursacht eine Biegung oder einen „Knick“, der verhindert, dass die Fettsäuren fest gepackt werden und sie bei Raumtemperatur flüssig bleiben. Beispiele für ungesättigte Fette sind Olivenöl, Maisöl, Rapsöl und Lebertran. Ungesättigte Fette helfen, den Cholesterinspiegel im Blut zu senken; wohingegen gesättigte Fette zur Plaquebildung in den Arterien beitragen. Trans-Fette Die Lebensmittelindustrie hydriert Öle künstlich, um ihnen eine halbfeste Konsistenz zu verleihen, die für viele verarbeitete Lebensmittelprodukte wünschenswert ist. Dabei können sich Doppelbindungen der cis-Konformation in der Kohlenwasserstoffkette in Doppelbindungen der trans-Konformation umwandeln. Margarine, einige Arten von Erdnussbutter und Backfett sind Beispiele für künstlich gehärtete Transfette. Jüngste Studien haben gezeigt, dass ein Anstieg der Transfette in der menschlichen Ernährung zu einem höheren Gehalt an Lipoproteinen niedriger Dichte (LDL) oder „schlechtem“ Cholesterin führen kann, was wiederum zu Plaqueablagerungen in den Arterien leitet, was Herzerkrankungen verursachen kann. Omega-Fettsäuren Essentielle Fettsäuren sind solche, die der menschliche Körper benötigt, aber nicht synthetisiert. Sie müssen daher über die Nahrung zugeführt werden. Omega-3-Fettsäuren fallen in diese Kategorie und sind eine von nur zwei, die für den Menschen bekannt sind (die andere ist Omega-6-Fettsäure). Dies sind mehrfach ungesättigte Fettsäuren und zählen zu den Omega-3-Fettsäuren, da eine Doppelbindung den dritten Kohlenstoff vom Ende der Kohlenwasserstoffkette mit dem benachbarten Kohlenstoff verbindet. Alpha-Linolensäure ist ein Beispiel für eine Omega-3-Fettsäure. Es verfügt über drei cis-Doppelbindungen und hat dadurch eine gekrümmte Form. Lachs, Forelle und Thunfisch sind gute Quellen für Omega-3-Fettsäuren. Untersuchungen zeigen, dass Omega-3-Fettsäuren das Risiko eines plötzlichen Herzinfarkttodes verringern, die Triglyceride im Blut senken, den Blutdruck senken und Thrombosen vorbeugen, indem sie die Blutgerinnung hemmen. Sie reduzieren auch Entzündungen und können dazu beitragen, das Risiko einiger Krebsarten bei Tieren zu senken. Dieser Text wurde angepasst von <a href="https://openstax.org/books/biology-2e/pages/3-3-lipids">Openstax, Biology 2e, Chapter 3.3: Lipids</a>.

Struktur von Lipiden

Lipide umfassen eine vielfältige Gruppe von Verbindungen, die in der Natur weitgehend unpolar sind. Dies liegt daran, dass es sich um Kohlenwasserstoffe handelt, die meist unpolare ...

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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

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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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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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Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. [Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.]

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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

Lipids, Fats, and Cell Membranes

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