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The general trend toward higher content of long chain PUFA at lower temperatures is quite clear. If the trends in fatty acid composition can be taken as clues to the EFA requirements of fish, the w 3 requirement would be greater for fish raised at lower temperatures. Fish raised in warmer waters, such as common carp, channel catfish, and tilapia may do better with a mixture of w 6 and w 3 fatty acids.

Commercially available trout pellets are often low in w 3 PUFA and high in w 6 fatty acids. It is important not to ignore the effect of dietary lipid composition on fatty acid composition of fish fed artificial diets. When the dietary ratio is very high in w 6 fatty acids supplied by animal lard or vegetable oils, there is a tendency for fish to alter the ratio of PUFA incorporated in favour of w 3 fatty acids.

Seasonal changes have been observed in total lipid and iodine values of herring oils. The iodine value or degree of unsaturation of the oil was minimal in April and maximal in June. The great increase in unsaturation corresponded to the onset of feeding in spring. The absence of a gas liquid chromatograph GLC at the time precluded identification of changes in individual fatty acids.

Flesh and viscera lipid content of the sardine Sardinops melanosticta vary from 3. The fatty acids of principal interest with respect to EFA metabolism are w 6, w 3, and w 3. There was considerable variation in all of these fatty acids in both neutral and polar lipid from both tissues. In the flesh, the w 6 was consistently higher in the neutral lipid than in the polar lipid.

The total w 3 plus w 3 was consistently higher in polar lipid than in the neutral lipid. Thus, in spite of the major fluctuations in fatty acids caused by changes in diet and temperature throughout the seasons, there was a consistent preferential incorporation of PUFA of the w 3 series into the polar or phospholipid fraction of the lipids. One of the best clues to the EFA requirements of a species can be gained from the fatty acid composition of the lipids incorporated into the offspring or egg.

The act of reproduction or spawning also has a significant effect on the seasonal fluctuation of lipids in fish.

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Fatty acid composition of fish egg lipids is probably distinctive for each species and contains increased levels of , w 6, w 3 and w 3 compared to the liver lipids of the same female fish Ackman, Elevated levels of , w 3, and w 3 and reduced in the ovary occurred compared to mesenteric fat of Pacific sardine fed a natural copepod diet.

The blood fatty acids of the sardine fed the natural diet were similar to those of the ovary. When the sardines were fed trout food, both the blood and mesenteric fat responded to the diet with elevated w 6 and reduced w 3 arid w 3. The effect of the diet on ovary fatty acid content was considerably less, as relatively high levels of w 3 and w 3 were retained. The ovary lipids of the sweet smelt show an increase in , and a reduction in the PUFA, especially in the phospholipids, compared to the lipids from the flesh of fish caught at the same time of year.

The hatchability of eggs from common carp fed several different formulated feeds is greatly reduced when the w 3 of the egg lipids is less than 10 percent. Further, the muscle, plasma, and erythrocyte fatty acid compositions are more affected by dietary lipid than those of the eggs.

The EFA requirements of a number of species of fish have been investigated in nutritional studies. The fish themselves have given ample evidence for EFA preference by the types of fatty acids they incorporate into their lipids. Fish, in general, tend to utilize w 3 over w 6. The lipids of the egg must satisfy the EFA requirement of the embryo until it is able to feed. The fatty acid composition data suggest that the w 3 requirement is greater in seawater than in freshwater and higher in cold water than in warm water.

Information on the lipid composition of fish can be used to make some guesses about dietary lipid requirements. Linolenic acid w 3 resulted in some sparing action and growth promotion in rats, and fatty acids of the w 6 EFA prevented all of the EFA-deficiency symptoms. Research with homeothermic land-dwelling animals showed that the w 6 series of fatty acids are the "essential fatty acids", while the w 3 series are considered to be non-essential or only have a partial sparing action on EFA-deficiency.

The w 6 series of fatty acids have been shown to be essential to enough species that it began to become accepted that these are the essential fatty acids for all animals. It was assumed by many that fish also required w 6 fatty acids. Many researchers began by supplementing fish diets with vegetable oils, such as corn, peanut, or sunflower oil, which were rich in linoleic acid. The main sympton observed during the development of EFA deficiency in chinook salmon fed fat-free diets was a marked depigmentation that can be prevented by addition of 1 percent trilinolein, but not by 0.

Although the w 6 fatty acids are considered to be essential, one of the general characteristics of fish oils is the low levels of w 6 series fatty acids and the higher levels of w 3 type fatty acids. There is evidence that polyunsaturated fatty acids PUPA of the w 3 series, which are present in relatively large concentrations in fish oil, play the role of essential fatty acid for fish.

Dietary fish oil is superior to corn oil in promoting growth of rainbow trout Salmo gairdneri and the yellow-tail Seriola guingueradiata. Dietary linolenic acid or ethyl linolenate w 3 gives a positive growth response for rainbow trout which may be attributed to a dietary requirement for w 3 fatty acids. One of the most widely accepted theories explaining the presence of such high levels of w 3 and w 3 fatty acids in fish oils is related to the effect of unsaturation on the melting point of a lipid.

The greater degree of unsaturation of fatty acids in the fish phospholipids allows for flexibility of cell membrane at lower temperatures. The w 3 structure allows a greater degree of unsaturation than the w 6 or w 9. This theory is consistent with the fact that cold water fish have a greater nutritional requirement for w 3 fatty acids, while the EFA requirement of some warm water fish can be satisfied by a mixture of w 6 plus w 3.

The EFA requirement can be met by 1 percent w 3 in the diet.

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  8. Inclusion of w 6 in the diet may result in some improvement in growth and feed conversion compared to EFA deficient diets; however, the w 6 fatty acids will not prevent some EFA deficiency symptoms such as the "shock syndrome". Although it is clear that rainbow trout require w 3 fatty acids, it remains to be shown conclusively whether some dietary level of w 6 fatty acid is essential. In all the above studies with rainbow trout, dietary w 6 or w 3 were readily converted to C and C PUFA of the same series, and w 3 or w 3 had similar EFA value for rainbow trout.

    Either w 3 or w 3 is superior to w 3 in an EFA value for rainbow trout, and the former two fatty acids in combination are superior to either alone.

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    This is consistent with data for mammals, where w 6 has higher EFA value than w 6. The superior nutritional value of C and C carbon w 3-PUFA is further supported by the excellent growth promoting effects of dietary fish oils such as pollock liver oil and salmon oil for rainbow trout.

    The quantitative EFA requirement of the catfish has not yet been determined. However, the evidence is convincing that the w 3 requirement is not as great as that of rainbow trout. Analysis of fatty acids of lipids from catfish purchased at five processing plants showed very low levels of w 6, w 3, and w 3; 0. Of the four molecules of life , lipids arguably have the greatest variation in their basic structure and are far more difficult to define than proteins , carbohydrate and nucleic acids.

    Almost all lipids are insoluble in water. They are known as hydrophobic molecules because they are repelled by water. Lipids are essential for all life on Earth. They play many important roles in maintaining the health of an organism. Arguably the most important function lipids perform is as the building blocks of cellular membranes. Other functions include energy storage, insulation, cellular communication and protection.

    The plasma membrane around a cell provides a barrier that separates the contents of a cell from the external world. It is responsible for controlling what substances enter and leave a cell. They perform particular tasks such as photosynthesis and respiration. Organelles are the key feature of eukaryotic cells that have made plants, animals and fungi so efficient at using resources.

    Lipids play an important role in storing energy. If an animal eats an excessive amount of energy it is able to store the energy for later use in fat molecules. Fat molecules can store a very high amount of energy for their size which is important for animals because of our mobile life styles. Fats are important for heat insulation. Marine mammals , such as seals, dolphins and whales, offer a perfect example of how fats can provide insulation. Blubber covers their entire bodies apart from their fins and head and prevents water from cooling their internal body temperatures.

    The layer of blubber also makes their bodies extremely streamlined for moving through water. Fats also provide a protective layer around important organs in animals such as our liver and kidneys. Steroids are a group of lipids involved in cellular communication. A number of steroids are hormones and are important for many processes in the body including growth, sexual development, regulating metabolism and immune defense.

    There is a huge variety of different lipids and the chemical structure varies between each of them.

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    Because of this it is difficult to outline a general structure of a lipid. All lipids do however contain at least one hydrocarbon chain i. Hydrocarbon chains are insoluble in water. The vast majority of lipids have long hydrocarbon chains which is why they are hydrophobic molecules i.

    Fatty acids are a defining feature of lipids. A fatty acid is a long hydrocarbon alkyl chain with an acidic head. A fatty acid can be saturated or unsaturated.

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    If there is no double bonds along the alkyl chain, the fatty acid is saturated. This is because all of the carbon atoms have bonded to as many hydrogen atoms as possible. The alkyl chain is therefore saturated in hydrogen. The presence of a double bond makes a fatty acid unsaturated because it is possible for the alkyl chain to be bonded to more hydrogen atoms.

    Fats are a common and well-known form of lipids. They are made by bonding fatty acids to an alcohol. In the saccharolipids, a monosaccharide substitutes for the glycerol backbone present in glycerolipids and glycerophospholipids. The minimal lipopolysaccharide required for growth in E.

    Properties of Lipids

    Polyketides are synthesized by polymerization of acetyl and propionyl subunits by classic enzymes as well as iterative and multimodular enzymes that share mechanistic features with the fatty acid synthases. They comprise a large number of secondary metabolites and natural products from animal, plant, bacterial, fungal and marine sources, and have great structural diversity. Many commonly used anti-microbial , anti-parasitic , and anti-cancer agents are polyketides or polyketide derivatives, such as erythromycins , tetracyclines , avermectins , and antitumor epothilones.

    Eukaryotic cells feature the compartmentalized membrane-bound organelles that carry out different biological functions. The glycerophospholipids are the main structural component of biological membranes , as the cellular plasma membrane and the intracellular membranes of organelles ; in animal cells, the plasma membrane physically separates the intracellular components from the extracellular environment. Plant thylakoid membranes have the largest lipid component of a non-bilayer forming monogalactosyl diglyceride MGDG , and little phospholipids; despite this unique lipid composition, chloroplast thylakoid membranes have been shown to contain a dynamic lipid-bilayer matrix as revealed by magnetic resonance and electron microscope studies.

    A biological membrane is a form of lamellar phase lipid bilayer. The formation of lipid bilayers is an energetically preferred process when the glycerophospholipids described above are in an aqueous environment.

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    In an aqueous system, the polar heads of lipids align towards the polar, aqueous environment, while the hydrophobic tails minimize their contact with water and tend to cluster together, forming a vesicle ; depending on the concentration of the lipid, this biophysical interaction may result in the formation of micelles , liposomes , or lipid bilayers. Other aggregations are also observed and form part of the polymorphism of amphiphile lipid behavior.

    Phase behavior is an area of study within biophysics and is the subject of current [ when? So in an aqueous environment, the water molecules form an ordered " clathrate " cage around the dissolved lipophilic molecule. The formation of lipids into protocell membranes represents a key step in models of abiogenesis , the origin of life. Triglycerides, stored in adipose tissue, are a major form of energy storage both in animals and plants. They are a major source of energy because carbohydrates are fully reduced structures. In comparison to glycogen which would contribute only half of the energy per its pure mass, triglyceride carbons are all bonded to hydrogens, unlike in carbohydrates.

    Migratory birds that must fly long distances without eating use stored energy of triglycerides to fuel their flights. In recent years, evidence has emerged showing that lipid signaling is a vital part of the cell signaling.


    They accomplish this by being exposed to the extracellular face of the cell membrane after the inactivation of flippases which place them exclusively on the cytosolic side and the activation of scramblases, which scramble the orientation of the phospholipids. After this occurs, other cells recognize the phosphatidylserines and phagocytosize the cells or cell fragments exposing them. Acyl-carnitines are involved in the transport and metabolism of fatty acids in and out of mitochondria, where they undergo beta oxidation.

    Polyprenol phosphate sugars and polyprenol diphosphate sugars function in extra-cytoplasmic glycosylation reactions, in extracellular polysaccharide biosynthesis for instance, peptidoglycan polymerization in bacteria , and in eukaryotic protein N- glycosylation. The major dietary lipids for humans and other animals are animal and plant triglycerides, sterols, and membrane phospholipids. The process of lipid metabolism synthesizes and degrades the lipid stores and produces the structural and functional lipids characteristic of individual tissues.

    In animals, when there is an oversupply of dietary carbohydrate, the excess carbohydrate is converted to triglycerides. This involves the synthesis of fatty acids from acetyl-CoA and the esterification of fatty acids in the production of triglycerides, a process called lipogenesis. The acyl chains in the fatty acids are extended by a cycle of reactions that add the acetyl group, reduce it to an alcohol, dehydrate it to an alkene group and then reduce it again to an alkane group. The enzymes of fatty acid biosynthesis are divided into two groups, in animals and fungi all these fatty acid synthase reactions are carried out by a single multifunctional protein, [88] while in plant plastids and bacteria separate enzymes perform each step in the pathway.

    The synthesis of unsaturated fatty acids involves a desaturation reaction, whereby a double bond is introduced into the fatty acyl chain. For example, in humans, the desaturation of stearic acid by stearoyl-CoA desaturase-1 produces oleic acid. Triglyceride synthesis takes place in the endoplasmic reticulum by metabolic pathways in which acyl groups in fatty acyl-CoAs are transferred to the hydroxyl groups of glycerolphosphate and diacylglycerol.

    Terpenes and isoprenoids , including the carotenoids , are made by the assembly and modification of isoprene units donated from the reactive precursors isopentenyl pyrophosphate and dimethylallyl pyrophosphate. In animals and archaea , the mevalonate pathway produces these compounds from acetyl-CoA, [93] while in plants and bacteria the non-mevalonate pathway uses pyruvate and glyceraldehyde 3-phosphate as substrates. Here, the isoprene units are joined together to make squalene and then folded up and formed into a set of rings to make lanosterol.

    Beta oxidation is the metabolic process by which fatty acids are broken down in the mitochondria or in peroxisomes to generate acetyl-CoA. For the most part, fatty acids are oxidized by a mechanism that is similar to, but not identical with, a reversal of the process of fatty acid synthesis. That is, two-carbon fragments are removed sequentially from the carboxyl end of the acid after steps of dehydrogenation , hydration , and oxidation to form a beta-keto acid , which is split by thiolysis.

    Hence the citric acid cycle can start at acetyl-CoA when fat is being broken down for energy if there is little or no glucose available. The energy yield of the complete oxidation of the fatty acid palmitate is ATP. Most of the fat found in food is in the form of triglycerides, cholesterol, and phospholipids. Some dietary fat is necessary to facilitate absorption of fat-soluble vitamins A , D , E , and K and carotenoids.

    Most vegetable oils are rich in linoleic acid safflower , sunflower , and corn oils. Alpha-linolenic acid is found in the green leaves of plants, and in selected seeds, nuts, and legumes in particular flax , rapeseed , walnut , and soy. Fats that are good for you can be turned into trans fats by overcooking. A few studies have suggested that total dietary fat intake is linked to an increased risk of obesity [] [] and diabetes. The Nutrition Source, a website maintained by the Department of Nutrition at the Harvard School of Public Health , summarizes the current evidence on the impact of dietary fat: "Detailed research—much of it done at Harvard—shows that the total amount of fat in the diet isn't really linked with weight or disease.

    From Wikipedia, the free encyclopedia. A substance of biological origin that is soluble in nonpolar. Organic Chemistry. Journal of Lipid Research. Chemical Reviews. International Journal of Molecular Sciences. Human Biology and Health. Sur la nature des corps gras. XCIII, p. Recherches sur les corps gras d'origine animale.

    Levrault, Paris, Introduction to Lipidomics. Introduction, History and Evolution. In: Lipids. Nutrition and health. Chronological history of lipid center. Cyberlipid Center. Last updated on 11 November Fats, Lipoids. In: Handbook of Histopathological Techniques. London, Butterworths, 3rd ed.

    A: Introduction to Lipids - Biology LibreTexts

    A proposed chemical classification of lipins. Biochemical Bulletin , , v. The Oily Press, Bridgwater, England. Biochemistry of Lipids, Lipoproteins and Membranes. Amsterdam: Elsevier. Methods in Enzymology.