Fatty acid/ja: Difference between revisions

==脂肪酸の長さ===

===不飽和脂肪酸===

; シス型とは、二重結合に隣接する2つの水素原子が鎖の同じ側に突き出ている状態を意味する。二重結合の剛性はそのコンフォメーションを凍結させ、''シス''異性体の場合は鎖を曲げ、脂肪酸のコンフォメーションの自由度を制限する。シス''配置の二重結合が多ければ多いほど、鎖の柔軟性は低くなる。鎖が多くの''シス''結合を持つ場合、最もアクセスしやすいコンフォーメーションではかなり湾曲する。例えば、二重結合が1つの[[oleic acid/ja|オレイン酸]]は「キンク」を持つが、二重結合が2つの[[linoleic acid/ja|リノール酸]]はより顕著な曲がりを持つ。二重結合が3つの[[α-Linolenic acid/ja|α-リノレン酸]]は、鉤状の形状を好む。この効果は、脂肪酸が脂質二重層中のリン脂質や脂質滴中のトリグリセリドの一部であるような制限された環境では、シス結合が脂肪酸が密に詰まる能力を制限するため、膜や脂肪の融解温度に影響を与える可能性があるということである。しかし、シス型不飽和脂肪酸は細胞膜の流動性を高めるが、トランス型不飽和脂肪酸はそうではない。

; トランス型とは、隣接する2つの水素原子が鎖の「反対側」にあることを意味する。その結果、鎖はあまり曲がらず、その形状は直鎖飽和脂肪酸に似ている。

===偶数鎖脂肪酸と奇数鎖脂肪酸====  

===分岐===

===炭素原子番号===

===脂肪酸の命名法====

|'''Δ^''x'''''（または'''δ-''x'''''）'''命名法'''では、各二重結合はΔ^''x''で示され、二重結合は''x''番目の炭素-炭素結合から始まる、 二重結合は分子骨格の[[carboxylic group/ja|カルボキシル]]末端から[[#Numbering of the carbon atoms in a fatty acid|数]]番目の炭素-炭素結合''x''から始まる。各二重結合の前には''[[cis-trans isomerism/ja|シス]]''-または''[[cis-trans isomerism/ja|トランス]]''-の接頭辞が付き、結合周辺の分子の配置を示す。例えば、[[linoleic acid/ja|リノール酸]]は「''シス''-Δ⁹, ''シス''-Δ¹²オクタデカジエン酸」と命名される。この命名法は、系統的命名法よりも冗長でないという利点があるが、技術的には明確でも説明的でもない。

|'''''n''−''x'''''（''''n'' マイナス ''x''、または '''ω−''x''''' または '''オメガ-''x'''''）'''命名法'''は、個々の化合物に名前を付けるだけでなく、それらを動物の生合成特性に基づいて分類する。二重結合は、分子の骨格の[[Methyl group/ja|メチル]]末端から[[#Numbering of the carbon atoms in a fatty acid|数えて]] ''x''^th の炭素-炭素結合に位置している。たとえば、[[α-Linolenic acid/ja|α-リノレン酸]]は、[[omega-3 fatty acid/ja|''n''−3]]または[[omega-3/ja|omega-3]]脂肪酸として分類されるため、このタイプの他の化合物と同じ生合成経路を共有する可能性がある。''ω−''x''''、''omega-''x''''、または「omega」の表記法は一般的に栄養の文献で見られるが、[[IUPAC nomenclature/ja|IUPAC]]はこれを技術文書では''n''−''x''表記法に代わりにし、非推奨としている。最も一般的に研究されている脂肪酸生合成経路には、[[omega-3 fatty acid/ja|''n''−3]]および[[omega-6 fatty acid/ja|''n''−6]]がある。

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===Metabolism===

{{Main|Fatty acid metabolism}}

Fatty acids are broken down to CO{{sub|2}} and water by the intra-cellular [[mitochondria]] through [[beta oxidation]] and the [[citric acid cycle]]. In the final step ([[oxidative phosphorylation]]), reactions with oxygen release a lot of energy, captured in the form of large quantities of [[Adenosine triphosphate|ATP]]. Many cell types can use either [[glucose]] or fatty acids for this purpose, but fatty acids release more energy per gram. Fatty acids (provided either by ingestion or by drawing on triglycerides stored in fatty tissues) are distributed to cells to serve as a fuel for muscular contraction and general metabolism.

====Essential fatty acids====

{{Main|Essential fatty acid}}

Fatty acids that are required for good health but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food, are called essential fatty acids. There are two series of essential fatty acids: one has a double bond [[Omega-3 fatty acid|three carbon atoms]] away from the methyl end; the other has a double bond [[Omega-6 fatty acid|six carbon atoms]] away from the methyl end. Humans lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10, as counted from the carboxylic acid side. Two essential fatty acids are [[linoleic acid]] (LA) and [[α-Linolenic acid|alpha-linolenic acid]] (ALA). These fatty acids are widely distributed in plant oils. The human body has a limited ability to convert ALA into the longer-chain [[omega-3 fatty acid]]s — [[eicosapentaenoic acid]] (EPA) and [[docosahexaenoic acid]] (DHA), which can also be obtained from fish. Omega-3 and [[Omega-6 fatty acid|omega-6]] fatty acids are [[Biosynthesis|biosynthetic]] precursors to [[Cannabinoid#Endocannabinoids|endocannabinoids]] with [[Nociception|antinociceptive]], [[anxiolytic]], and [[Nervous system|neurogenic]] properties.

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===Distribution===

{{Main|Blood fatty acids}}

Blood fatty acids adopt distinct forms in different stages in the blood circulation. They are taken in through the intestine in [[chylomicron]]s, but also exist in [[very low density lipoprotein]]s (VLDL) and [[low density lipoprotein]]s (LDL) after processing in the liver. In addition, when released from [[adipocytes]], fatty acids exist in the blood as [[free fatty acids]].

It is proposed that the blend of fatty acids exuded by mammalian skin, together with [[lactic acid]] and [[pyruvic acid]], is distinctive and enables animals with a keen sense of smell to differentiate individuals.

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==Skin==

The [[stratum corneum]] {{ndash}} the outermost layer of the [[epidermis]] {{ndash}} is composed of terminally [[Cellular differentiation|differentiated]] and [[Enucleation (microbiology)|enucleated]] [[corneocyte]]s within a lipid matrix. Together with [[cholesterol]] and [[ceramide]]s, free fatty acids form a water-impermeable barrier that prevents [[evaporation|evaporative water loss]]. Generally, the epidermal lipid matrix is composed of an equimolar mixture of ceramides (about 50% by weight), cholesterol (25%), and free fatty acids (15%). Saturated fatty acids 16 and 18 carbons in length are the dominant types in the epidermis, while unsaturated fatty acids and saturated fatty acids of various other lengths are also present. The relative abundance of the different fatty acids in the epidermis is dependent on the body site the skin is covering. There are also characteristic epidermal fatty acid alterations that occur in [[psoriasis]], [[atopic dermatitis]], and other [[inflammation|inflammatory conditions]].

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==Analysis==

The chemical analysis of fatty acids in lipids typically begins with an [[interesterification]] step that breaks down their original esters (triglycerides, waxes, phospholipids etc.) and converts them to [[methyl]] esters, which are then separated by gas chromatography or analyzed by [[gas chromatography]] and mid-[[infrared spectroscopy]].

Separation of unsaturated isomers is possible by [[Argentation chromatography|silver ion complemented thin-layer chromatography]]. Other separation techniques include [[high-performance liquid chromatography]] (with short columns packed with [[silica gel]] with bonded phenylsulfonic acid groups whose hydrogen atoms have been exchanged for silver ions). The role of silver lies in its ability to form complexes with unsaturated compounds.