Some common lipids. At the top is oleic acid and cholesterol. Oleic acid is a Monounsaturated omega-9 Fatty acid found in various animal and vegetable sources Cholesterol is a Lipid found in the Cell membranes and transported in the Blood plasma of all Animals It is an essential component of mammalian In the middle is a triglyceride composed of oleoyl, stearoyl, and palmitoyl chains attached to a glycerol backbone. (more properly known as, TAG or triacylglyceride) is Glyceride in which the Glycerol is Esterified with three Fatty acids It is the Oleic acid is a Monounsaturated omega-9 Fatty acid found in various animal and vegetable sources Stearic acid (first syllable rhymes with either bear or gear) ( IUPAC Systematic name: octadecanoic acid) is a saturated Palmitic acid,CH3(CH214COOH or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated Fatty acids found in animals At the bottom is the common phospholipid phosphatidylcholine. Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate Phosphatidylcholines are a class of Phospholipids which incorporate Choline as a headgroup

Lipids are broadly defined as any fat-soluble (lipophilic), naturally-occurring molecule, such as fats, oils, waxes, cholesterol, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. Lipophilicity, fat-liking, refers to the ability of a Chemical compound to dissolve in fats oils lipids and non-polar solvents such as Hexane or In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by A vitamin is an Organic compound required as a Nutrient in tiny amounts by an Organism. A monoglyceride, more correctly known as a monoacylglycerol, is a Glyceride consisting of one Fatty acid chain Covalently bonded to a Glycerol A diglyceride, or a diacylglycerol (DAG is a Glyceride consisting of two Fatty acid chains covalently bonded to a Glycerol Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate The main biological functions of lipids include energy storage, acting as structural components of cell membranes, and participating as important signaling molecules. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer Lipid signaling broadly defined refers to any biological signaling event involving a Lipid messenger that binds and activates a receptor.

Although the term lipid is sometimes used as a synonym for fats, fats are a subgroup of lipids called triglycerides and should not be confused with the term fatty acid. Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water (more properly known as, TAG or triacylglyceride) is Glyceride in which the Glycerol is Esterified with three Fatty acids It is the In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which Lipids also encompass molecules such as fatty acids and their derivatives (including tri-, di-, and monoglycerides and phospholipids), as well as other sterol-containing metabolites such as cholesterol. (more properly known as, TAG or triacylglyceride) is Glyceride in which the Glycerol is Esterified with three Fatty acids It is the A diglyceride, or a diacylglycerol (DAG is a Glyceride consisting of two Fatty acid chains covalently bonded to a Glycerol A monoglyceride, more correctly known as a monoacylglycerol, is a Glyceride consisting of one Fatty acid chain Covalently bonded to a Glycerol Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate Sterols, or steroid alcohols are a subgroup of Steroids with a Hydroxyl group at the 3-position of the A-ring Metabolomics is the "systematic study of the unique chemical fingerprints that specific cellular processes leave behind" - specifically the study of their small-molecule metabolite Cholesterol is a Lipid found in the Cell membranes and transported in the Blood plasma of all Animals It is an essential component of mammalian ^[1] The emulsion test is a crude method for determining the presence or absence of lipids in a given sample. The emulsion test is a method to determine the presence of Lipids using Wet chemistry.

Lipids are a diverse group of compounds that have many key biological functions, such as acting as structural components of cell membranes, serving as energy storage sources and participating in signaling pathways. Lipids may be broadly defined as hydrophobic or amphiphilic small molecules that originate entirely or in part from two distinct types of biochemical subunits or "building blocks": ketoacyl and isoprene groups. In Chemistry, hydrophobicity (from the combining form of water in Attic Greek hydro- and for fear phobos) refers to the physical property of Amphiphile (from the Greek αμφις amphis both and φιλíα Philia: love friendship is a term describing a Chemical compound possessing both A ketone (pronounced as key tone) is either the Functional group characterized by a Carbonyl group (O=C linked to two other Carbon atoms or Isoprene is a common synonym for the chemical compound 2-methylbuta-13-diene ^[2] Using this approach, lipids may be divided into eight categories : fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, saccharolipids and polyketides (derived from condensation of ketoacyl subunits); and sterol lipids and prenol lipids (derived from condensation of isoprene subunits).

Categories of Lipids

Examples of some lipids from various categories.

• Fatty acyls (including fatty acids) are a diverse group of molecules synthesized by chain-elongation of an acetyl-CoA primer with malonyl-CoA or methylmalonyl-CoA groups. In Chemistry, especially Biochemistry, a fatty acid is a Carboxylic acid often with a long unbranched Aliphatic tail ( chain) which Acetyl-CoA is an important molecule in metabolism used in many biochemical reactions Malonyl-CoA is a Coenzyme A derivative Functions It plays a key role in chain elongation in Fatty acid biosynthesis and Polyketide biosynthesis Methylmalonyl-CoA is the Coenzyme A linked form of Methylmalonic acid. ^[3][4] The fatty acyl structure represents the major lipid building block of complex lipids and therefore is one of the most fundamental categories of biological lipids. The carbon chain may be saturated or unsaturated, and may be attached to functional groups containing oxygen, halogens, nitrogen and sulfur. Examples of biologically interesting fatty acyls are the eicosanoids which are in turn derived from arachidonic acid which include prostaglandins, leukotrienes, and thromboxanes. In biochemistry eicosanoids are signaling molecules made by Oxygenation of twenty-carbon Essential fatty acids (EFAs A prostaglandin is any member of a group of Lipid compounds that are derived enzymatically from Fatty acids and have important functions in the Animal body Leukotrienes are naturally produced Eicosanoid lipid mediators, which may be responsible for the effects of an inflammatory response Thromboxane is a member of the family of Lipids known as Eicosanoids. Other major lipid classes in the fatty acyl category are the fatty esters and fatty amides. Fatty esters include important biochemical intermediates such as wax esters, fatty acyl thioester coenzyme A derivatives, fatty acyl thioester ACP derivatives and fatty acyl carnitines. An Ester, found in some Fish such as Orange roughy, Oilfish, Escolar, Black oreo, Smooth oreo and other fish primarily Coenzyme A ( CoA, CoASH, or HSCoA) is a Coenzyme, notable for its role in the synthesis and oxidation of Fatty acids The fatty amides include N-acyl ethanolamines such as anandamide. Anandamide, also known as arachidonoylethanolamide or AEA, is an endogenous cannabinoid Neurotransmitter found in animal and human organs especially

• Glycerolipids are composed mainly of mono-, di- and tri-substituted glycerols,^[5] the most well-known being the fatty acid esters of glycerol (triacylglycerols), also known as triglycerides. (more properly known as, TAG or triacylglyceride) is Glyceride in which the Glycerol is Esterified with three Fatty acids It is the these comprise the bulk of storage fat in animal tissues. Additional subclasses are represented by glycosylglycerols, which are characterized by the presence of one or more sugar residues attached to glycerol via a glycosidic linkage. Examples of structures in this category are the digalactosyldiacylglycerols found in plant membranes and seminolipid from mammalian spermatazoa.

• Glycerophospholipids, also referred to as phospholipids, are ubiquitous in nature and are key components of the lipid bilayer of cells, as well as being involved in metabolism and signaling. Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate Glycerophospholipids^[6] may be subdivided into distinct classes, based on the nature of the polar headgroup at the sn-3 position of the glycerol backbone in eukaryotes and eubacteria or the sn-1 position in the case of archaebacteria. Examples of glycerophospholipids found in biological membranes are phosphatidylcholine (also known as PC or GPCho, and lecithin), phosphatidylethanolamine (PE or GPEtn) and phosphatidylserine (PS or GPSer). MembraneA biological membrane or biomembrane is an enclosing or separating Amphipathic layer that acts as a barrier within or around a cell. Lecithin is any of a group of yellow-brownish fatty substances occurring in animal and plant tissues and in egg yolk composed of Phosphoric acid, Choline, In addition to serving as a primary component of cellular membranes and binding sites for intra- and intercellular proteins, some glycerophospholipids in eukaryotic cells, such as phosphatidylinositols and phosphatidic acids are either precursors of, or are themselves, membrane-derived second messengers. Phosphatidylinositol (abbreviated PtdIns or PI is a minor Phospholipid component in the cytosolic side of eukaryotic Cell membranes. Typically one or both of these hydroxyl groups are acylated with long-chain fatty acids, but there are also alkyl-linked and 1Z-alkenyl-linked (plasmalogen) glycerophospholipids, as well as dialkylether variants in prokaryotes.

• Sphingolipids are a complex family of compounds^[7] that share a common structural feature, a sphingoid base backbone that is synthesized de novo from serine and a long-chain fatty acyl CoA, then converted into ceramides, phosphosphingolipids, glycosphingolipids and other species. Ceramides are a family of Lipid molecules A ceramide is composed of Sphingosine and a Fatty acid. The major sphingoid base of mammals is commonly referred to as sphingosine. Sphingosine (2-amino-4-octadecene-13-diol is an 18-carbon Amino alcohol with an unsaturated hydrocarbon chain which forms a primary part of Sphingolipids a class Ceramides (N-acyl-sphingoid bases) are a major subclass of sphingoid base derivatives with an amide-linked fatty acid. The fatty acids are typically saturated or mono-unsaturated with chain lengths from 14 to 26 carbon atoms. The major phosphosphingolipids of mammals are sphingomyelins (ceramide phosphocholines), whereas insects contain mainly ceramide phosphoethanolamines and fungi have phytoceramidephosphoinositols and mannose containing headgroups. The Glycosphingolipids are a diverse family of molecules composed of one or more sugar residues linked via a glycosidic bond to the sphingoid base. Examples of these are the simple and complex glycosphingolipids such as cerebrosides and gangliosides. Cerebrosides are Glycosphingolipids which are important components in animal Muscle and Nerve Cell membranes Myelin is the most well Ganglioside is a compound composed of a Glycosphingolipid ( Ceramide and Oligosaccharide) with one or more Sialic acids (AKA N-acetylneuraminic

• Sterol lipids, such as cholesterol and its derivatives are an important component of membrane lipids,^[8] along with the glycerophospholipids and sphingomyelins. Cholesterol is a Lipid found in the Cell membranes and transported in the Blood plasma of all Animals It is an essential component of mammalian The steroids, which also contain the same fused four-ring core structure, have different biological roles as hormones and signaling molecules. A steroid is a Terpenoid Lipid characterized by a Carbon skeleton with four fused rings generally arranged in a 6-6-6-5 fashion The C18 steroids include the estrogen family whereas the C19 steroids comprise the androgens such as testosterone and androsterone. Estrogens (US otherwise oestrogens or œstrogens) are a group of Steroid compounds named for their importance in the Estrous cycle, Androgen is the generic term for any natural or synthetic compound usually a Steroid Hormone, that stimulates or controls the development and maintenance of masculine Testosterone is a Steroid hormone from the Androgen group In mammals testosterone is primarily secreted in the testes of males and the Ovaries Androsterone (ADT is a Steroid hormone with weak Androgenic activity The C21 subclass includes the progestogens as well as the glucocorticoids and mineralocorticoids. Glucocorticoids (GC are a class of Steroid hormones characterised by an ability to bind with the glucocorticoid receptor ( GR) and trigger similar effects The secosteroids, comprising various forms of vitamin D, are characterized by cleavage of the B ring of the core structure. Vitamin D is a group of fat-soluble Prohormones, the two major forms of which are vitamin D2 (or Ergocalciferol) and vitamin D3 (or Other examples of sterols are the bile acids and their conjugates,^[9] which in mammals are oxidized derivatives of cholesterol and are synthesized in the liver. Sterols, or steroid alcohols are a subgroup of Steroids with a Hydroxyl group at the 3-position of the A-ring Bile acids (also known as bile salts are Steroid Acids found predominantly in the Bile of Mammals.

Figure 2: Structure of the saccharolipid Kdo₂-Lipid A. Glucosamine residues in blue, Kdo residues in red, acyl chains in black and phosphate groups in green.

• Prenol lipids are synthesized from the 5-carbon precursors isopentenyl diphosphate and dimethylallyl diphosphate that are produced mainly via the mevalonic acid (MVA) pathway. Mevalonic acid is a key Organic compound in biochemistry It is a precursor in the biosynthetic pathway known as the HMG-CoA reductase pathway, that produces ^[10] The simple isoprenoids (linear alcohols, diphosphates, etc. ) are formed by the successive addition of C5 units, and are classified according to number of these terpene units. Terpenes are a large and varied class of Hydrocarbons, produced primarily by a wide variety of plants particularly Conifers though also by some insects such Structures containing greater than 40 carbons are known as polyterpenes. Carotenoids are important simple isoprenoids that function as anti-oxidants and as precursors of vitamin A. Carotenoids are organic Pigments that are naturally occurring in Chromoplasts of plants and some other photosynthetic Organisms Vitamin A refers to a family of similarly shaped molecules the Retinoids. Another biologically important class of molecules is exemplified by the quinones and hydroquinones, which contain an isoprenoid tail attached to a quinonoid core of non-isoprenoid origin. Vitamin E and vitamin K, as well as the ubiquinones, are examples of this class. See also Tocopherol, Tocotrienol Vitamin E is the collective name for a set of 8 related Tocopherols and Tocotrienols which are fat-soluble Vitamin K (K from "Koagulations-Vitamin" in German Danish Swedish and Norwegian denotes a group of Lipophilic, Hydrophobic Vitamins that Bacteria synthesize polyprenols (called bactoprenols) in which the terminal isoprenoid unit attached to oxygen remains unsaturated, whereas in animal polyprenols (dolichols) the terminal isoprenoid is reduced.

• Saccharolipids describe compounds in which fatty acids are linked directly to a sugar backbone, forming structures that are compatible with membrane bilayers. In the saccharolipids, a sugar substitutes for the glycerol backbone that is present in glycerolipids and glycerophospholipids. The most familiar saccharolipids are the acylated glucosamine precursors of the Lipid A component of the lipopolysaccharides in Gram-negative bacteria. Glucosamine (C6H13NO5 is an Amino sugar and a prominent precursor in the Biochemical synthesis of glycosylated proteins Lipopolysaccharides ( LPS) are large Molecules consisting of a Lipid and a Polysaccharide joined by a Covalent bond; they are found Typical lipid A molecules are disaccharides of glucosamine, which are derivatized with as many as seven fatty-acyl chains. The minimal lipopolysaccharide required for growth in E. coli is Kdo₂-Lipid A, a hexa-acylated disaccharide of glucosamine that is glycosylated with two 3-deoxy-D-manno-octulosonic acid (Kdo) residues. ^[11]

• 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. In Organic chemistry, acetyl (ethanoyl is a Functional group, the Acyl of Acetic acid, with Chemical formula - C[[Oxygen They comprise a very large number of secondary metabolites and natural products from animal, plant, bacterial, fungal and marine sources, and have great structural diversity. ^[12] Many polyketides are cyclic molecules whose backbones are often further modified by glycosylation, methylation, hydroxylation, oxidation, and/or other processes. Polyketides are Secondary metabolites from bacteria, Fungi, Plants and Animals Polyketides are biosynthesized by the Many commonly used anti-microbial, anti-parasitic, and anti-cancer agents are polyketides or polyketide derivatives, such as erythromycins, tetracylines, avermectins, and antitumor epothilones. Erythromycin is a Macrolide Antibiotic that has an antimicrobial spectrum similar to or slightly wider than that of Penicillin, and is often used for people Avermectin is a family of Anti-parasitic drugs whose analogues include Ivermectin, Selamectin, Doramectin and Abamectin. History The structure of epothilone A was determined in 1996 using X-ray crystallography.

Biological Functions

Membranes

The glycerophospholipids are the main structural component of biological membranes, such as the cellular plasma membrane and the intracellular membranes of organelles. Glycerophospholipids or phosphoglycerides are Glycerol -based Phospholipids They are the main component of Biological membranes MembraneA biological membrane or biomembrane is an enclosing or separating Amphipathic layer that acts as a barrier within or around a cell. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed In animal cells the plasma membrane physically separates the intracellular components from the extracellular environment. All eukaryotic cells are compartmentalized into membrane-bound organelles which carry out different functions. These glycerophospholipids are amphipathic molecules that contain a glycerol core linked to two fatty acid-derived "tails" by ester or, more rarely, ether linkages and to one "head" group by a phosphate ester linkage. Ether is a class of Organic compounds which contain an ether group — an Oxygen Atom connected to two (substituted Alkyl A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. While glycerophospholipids are the major component of biological membranes, other non-glyceride lipid components such as sphingomyelin and sterols (mainly cholesterol in animal cell membranes) are also found in biological membranes. Sphingomyelin (SPH is a type of Sphingolipid found in animal Cell membranes, especially in the membranous Myelin sheath which surrounds some Nerve Sterols, or steroid alcohols are a subgroup of Steroids with a Hydroxyl group at the 3-position of the A-ring Cholesterol is a Lipid found in the Cell membranes and transported in the Blood plasma of all Animals It is an essential component of mammalian In plants and algae, the galactosyldiacylglycerols,^[13] and sulfoquinovosyldiacylglycerol,^[14] which lack a phosphate group, are important components of membranes of chloroplasts and related organelles and are the most abundant lipids in photosynthetic tissues, including those of higher plants, algae and certain bacteria.

Figure 3: Self-organization of phospholipids. Phospholipids are a class of Lipids and are a major component of all Biological membranes All phospholipids contain a Diglyceride, a Phosphate A lipid bilayer is shown on the left and a micelle on the right. A lipid bilayer or bilayer lipid membrane ( BLM) is a membrane composed of Lipid molecules (usually Phospholipids. A micelle (rarely micella, plural micelles) is an aggregate of Surfactant molecules dispersed in a liquid Colloid.

A biological membrane is a form of lipid bilayer, as is a liposome. A liposome is a tiny bubble ( vesicle) made out of the same material as a cell membrane. The formation of lipid bilayers is an energetically-preferred process when the glycerophospholipids described above are in an aqueous environment. Glycerophospholipids or phosphoglycerides are Glycerol -based Phospholipids They are the main component of Biological membranes In an aqueous system, the polar heads of lipids orientate towards the polar, aqueous environment, while the hydrophobic tails minimise their contact with water. The lipophilic tails of lipids (U) tend to cluster together, forming a lipid bilayer (1) or a micelle (2). A lipid bilayer or bilayer lipid membrane ( BLM) is a membrane composed of Lipid molecules (usually Phospholipids. A micelle (rarely micella, plural micelles) is an aggregate of Surfactant molecules dispersed in a liquid Colloid. Other aggregations are also observed and form part of the polymorphism of amphiphile (lipid) behaviour. Amphiphile (from the Greek αμφις amphis both and φιλíα Philia: love friendship is a term describing a Chemical compound possessing both The polar heads (P) face the aqueous environment, curving away from the water. Phase behaviour is a complicated area within biophysics and is the subject of current academic research. Polymorphism in biophysics is the aspect of the behaviour of Lipids that influences their long-range order i Micelles and bilayers form in the polar medium by a process known as the hydrophobic effect. The hydrophobic effect is the property that non-polar molecules tend to form intermolecular aggregates in an aqueous medium and analogous intramolecular interactions ^[15] When dissolving a lipophilic or amphiphilic substance in a polar environment, the polar molecules (i. e. water in an aqueous solution) become more ordered around the dissolved lipophilic substance, since the polar molecules cannot form hydrogen bonds to the lipophilic areas of the amphiphile. A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen Amphiphile (from the Greek αμφις amphis both and φιλíα Philia: love friendship is a term describing a Chemical compound possessing both So in an aqueous environment the water molecules form an ordered "clathrate" cage around the dissolved lipophilic molecule. A clathrate or clathrate compound or cage compound is a Chemical substance consisting of a lattice of one type of molecule trapping ^[16]

Energy storage and metabolism

Triacylglycerols, stored in adipose tissue, are a major form of energy storage in animals. Animals use triglycerides for energy storage because of its high caloric content (9 KCal/g), whereas plants, which do not require energy for movement, can afford to store food for energy in a less compact but more easily accessible form, such as starch (carbohydrate). Triglycerides and phospholipids are broken down into free fatty acids by the action of lipases. Beta oxidation is the process by which fatty acids, in the form of acyl-CoA molecules, are broken down in the mitochondria and/or in peroxisomes to generate acetyl-CoA. Beta oxidation is the process by which Fatty acids in the form of Acyl-CoA molecules are broken down in Mitochondria and/or in Peroxisomes to The acetyl CoA is then ultimately converted into ATP, CO2, and H2O using the citric acid cycle and the electron transport chain. Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle An electron transport chain couples a chemical reaction between an electron donor (such as NADH) and an electron acceptor (such as O2) to the transfer Conversely, fatty acid biosynthesis (Lipogenesis) takes place in the cytoplasm, using acetyl-CoA (derived from carbohydrates, amino acids or fatty acids) as the precursor^[17]. Lipogenesis is the process by which simple sugars such as Glucose are converted to Fatty acids which are subsequently esterified with Glycerol The fatty acids may be subsequently converted to triacylglycerols that are packaged in lipoproteins (VLDL's) and secreted from the liver. A lipoprotein is a biochemical assembly that contains both Proteins and Lipids The lipids or their derivatives may be covalently or non-covalently bound

Signaling

In recent years, evidence has emerged showing that lipid signaling is a vital part of the cell signaling. Lipid signaling broadly defined refers to any biological signaling event involving a Lipid messenger that binds and activates a receptor. Cell signaling is part of a Complex system of Communication that governs basic cellular activities and coordinates cell actions ^[18] Lipid signaling may occur via activation of GPCR's or nuclear receptors, and members of several different lipid categories have been identified as signaling molecules and cellular messengers. ^[19] These include sphingosine-1-phosphate, a sphingolipid derived from ceramide that is a potent messenger molecule involved in regulating calcium mobilization, cell growth, apoptosis; diacylglycerol(DAG) and the phosphatidylinositol phosphates (PIPs), involved in calcium-mediated activation of protein kinase C; the prostaglandins, arachidonic acid -derived fatty acids involved in inflammation and immunity; the steroid hormones such as estrogen, testosterone and cortisol, which modulate a host of functions such as reproduction, metabolism and blood pressure; and the oxysterols such as 25-hydroxy-cholesterol that are Liver X receptor (LXR) agonists. Sphingosine-1-phosphate (S1P is a signaling Sphingolipid. It is also referred to as a bioactive lipid mediator A diglyceride, or a diacylglycerol (DAG is a Glyceride consisting of two Fatty acid chains covalently bonded to a Glycerol Phosphatidylinositol (abbreviated PtdIns or PI is a minor Phospholipid component in the cytosolic side of eukaryotic Cell membranes. Protein kinase C ('PKC') is a family of protein kinases consisting of ~10 Isozymes. A prostaglandin is any member of a group of Lipid compounds that are derived enzymatically from Fatty acids and have important functions in the Animal body Estrogens (US otherwise oestrogens or œstrogens) are a group of Steroid compounds named for their importance in the Estrous cycle, Testosterone is a Steroid hormone from the Androgen group In mammals testosterone is primarily secreted in the testes of males and the Ovaries Cortisol is a Corticosteroid Hormone produced by the Adrenal gland (in the Zona fasciculata of the Adrenal cortex) The liver X receptor ( LXR) is a member of the Nuclear receptor family of Transcription factors and is closely related to nuclear receptors such as

Other functions

The "fat-soluble" vitamins (A, D, E and K) which are isoprene-based lipids are essential nutrients stored in the liver and fatty tissues. These have a diverse range of functions discussed elsewhere. Acyl-carnitines are involved in the transport and metabolism of fatty acids in and out of mitochondria, where they undergo beta oxidation. Polyprenols and their phosphorylated derivatives also play important transport roles, in this case the transport of oligosaccharides across membranes. Polyprenol phosphate sugars and polyprenol diphosphate sugars function in extra-cytoplasmic glycosylation reactions, in extra-cellular polysaccharide biosynthesis (for instance peptidoglycan polymerization in bacteria), and in eukaryotic protein N-glycosylation. ^[20] Cardiolipins are a subclass of glycerophospholipids containing four acyl chains and three glycerol groups that are particularly abundant in the inner mitochondrial membrane. They are believed to activate enzymes involved with oxidative phosphorylation. ^[21]

Nutrition and health

Lipids play diverse and important roles in nutrition and health. ^[22] Many lipids are absolutely essential for life. However, there is also considerable awareness that abnormal levels of certain lipids, particularly cholesterol (in hypercholesterolemia) and trans fatty acids, are risk factors for heart disease amongst others.

Humans have a requirement for certain essential fatty acids, such as linoleic acid (an omega-6 fatty acid) and alpha-linolenic acid (an omega-3 fatty acid) in the diet because they cannot be synthesized from simple precursors in the diet. Linoleic acid (LA is an unsaturated Omega-6 fatty acid. It is a colorless liquid α -Linolenic acid ( ALA) is an organic compound found in many common vegetable oils. Both of these fatty acids are 18-carbon polyunsaturated fatty acids differing in the number and position of the double bonds. 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 (flax, canola, walnuts and soy). Fish oils are particularly rich in the longer-chain omega-6 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Eicosapentaenoic acid (EPA or also icosapentaenoic acid is an Omega-3 fatty acid. Docosahexaenoic acid (commonly known as DHA; 226(ω-3 all-cis -docosa-4710131619-hexa- enoic acid Trivial name cervonic Most of the lipid found in food is in the form of triacylglycerols, cholesterol and phospholipids.

Most of the saturated fatty acids (as triacylglycerols) in the diet are incorporated into adipose tissue stores, because the absence of double bonds allows a higher energy yield per carbon than is obtained from oxidation of unsaturated fatty acids. The longer chain fatty acids are incorporated into cell membranes as phospholipids regardless of degree of saturation. Since dietary fatty acids are exchanged with membrane fatty acids, dietary fat composition is reflected in membrane lipid composition. Thus dietary fatty acids can influence cell function through effects on membrane properties. Dietary fat provides an average energy intake which is approximately twice that of carbohydrate or protein. A minimum amount of dietary fat is necessary to facilitate absorption of fat-soluble vitamins (A, D, E and K) and carotenoids. A minimal amount of body fat is also necessary to provide insulation that prevents heat loss and protects vital organs from shock due to ordinary activities.

High fat intake contributes to increased risk of obesity, diabetes and atherosclerosis. Atherosclerosis is the primary cause of coronary and cardiovascular diseases and is primary due to the buildup of plaque on the inside walls of arteries. Atherosclerosis is a Disease affecting arterial Blood vessels It is a chronic inflammatory response in the walls of arteries in large part due to the accumulation Plaque is made up of cholesterol-rich low density lipoproteins (LDL), macrophages, smooth muscle cells, platelets, and other substances. In North America and most other western countries, atherosclerosis is the leading cause of illness and death, almost doubling the number of deaths from cancers. Despite significant medical advances, coronary artery disease and atherosclerotic stroke are responsible for more deaths than all other causes combined. A substantial amount of scientific evidence supports the impact of dietary fatty acids on cardiovascular health. Saturated fats have a profound hypercholesterolemic (increase blood cholesterol levels) effect and tend to increase plasma LDL. They are found predominantly in animal products (butter, cheese and meat) but coconut oil and palm oil are common vegetable sources. Intake of monounsaturated fats in oils such as olive oil is thought to be preferable to consumption of polyunsaturated fats in oils such as corn oil because the monounsaturated fats apparently do not lower high-density-lipoprotein (HDL) cholesterol levels. ^[23] Keeping cholesterol in the normal range not only helps prevent heart attacks and strokes but may also prevent the progression of atherosclerosis. "Statins" are a class of drugs that lowers the level of cholesterol in the blood by inhibiting the enzyme HMG-CoA reductase. The statins (or HMG-CoA reductase inhibitors) form a class of hypolipidemic drugs used to lower Cholesterol levels in people with or at risk of Cardiovascular HMG-CoA reductase (or 3-hydroxy-3-methyl-glutaryl-CoA reductase or HMGR) is the rate controlling Enzyme ( of the Mevalonate pathway the This is a key enzyme involved in the biosynthesis of cholesterol in the liver.

References

See also

• Biochemistry
• Essential fatty acid
• Lipid signaling
• Saturation (chemistry)

External links

Introductory

• Lipid Library - General reference on lipid chemistry and biochemistry
• European Lipidomics Initiative - European research resource for lipid biochemistry. Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as Essential fatty acids, or EFAs are Fatty acids that cannot be constructed within an organism from other components (generally all references are to humans by any known chemical Lipid signaling broadly defined refers to any biological signaling event involving a Lipid messenger that binds and activates a receptor. In Chemistry, saturation has five different meanings In Physical chemistry, saturation is the point at which a Solution of a substance
• Cyberlipid.org - Resources and history for lipids.
• Science aid: Lipids - Resource for students
• Molecular Computer Simulations - Modeling of Lipid Membranes
• Lipids, Membranes and Vesicle Trafficking - The Virtual Library of Biochemistry and Cell Biology

Classification

• LIPID MAPS - LIPID Metabolites And Pathways Strategy

Nomenclature

• IUPAC nomenclature of lipids
• IUPAC glossary entry for the lipid class of molecules

Databases

• LIPID MAPS - Comprehensive lipid and lipid-associated gene/protein databases.
• LipidBank - Japanese database of lipids and related properties, spectral data and references.
• LIPIDAT - Database composed mainly of phospholipids and associated thermodynamic data.

General

• ApolloLipids - Provides dyslipidemia and cardiovascular disease prevention and treatment information as well as continuing medical education programs