What Term Refers to a Group of Compounds Including Triglycerides, Phospholipids, and Sterols?

Simple Lipid

The simplest lipid mixture shown to induce domain ("raft") formation consists of cholesterol and both a saturated and unsaturated species of phospholipid.

From: Electric current Topics in Membranes , 2017

FATS | Classification

M.H. Gordon , in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003

Unproblematic Lipids

The principal simple lipids are triglycerides (as well known as triacylglycerols), steryl esters, and wax esters. Hydrolysis of these lipids yields glycerol and fatty acids, sterols and fatty acids, and fatty alcohols plus fatty acids, respectively. The nigh important of these simple lipids for food scientists are the triglycerides. They are the major components of edible oils and fats, often representing more than 95% of refined oils. Triglycerides are esters of the trihydric booze glycerol with three fatty acids ( Figure 1). Many of the properties of triglycerides are dependent on the component fatty acids. Thus, the melting point of the triglyceride reflects the melting point of the component fatty acids, with iii loftier-melting-point fatty acids yielding a high-melting triglyceride. Unsaturation in the fat acids makes the triglyceride susceptible to autoxidation, simply as the fat acid itself would be. (Run across TRIGLYCERIDES | Structures and Properties.)

Figure 1. Triglyceride structure. Reproduced from Lipids, Encyclopaedia of Nutrient Science, Food Technology and Nutrition, Macrae R, Robinson RK and Sadler MJ (eds), 1993, Academic Press.

All triglycerides are susceptible to hydrolysis in the presence of a catalyst. Acids, bases, or enzymes belonging to the hydrolase grade, especially lipases, may deed equally the goad for the hydrolysis of triglycerides.

Steryl esters always occur together with sterols in plant, animal, or microbiological tissues. Wax esters may accrue in considerable amounts in some biological tissues and this class comprises the principal elective of beeswax and jojoba oil.

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Clinical Biochemistry

Buddhi Prakash Jain , ... Shweta Pandey , in Protocols in Biochemistry and Clinical Biochemistry, 2021

Definition

Triglycerides are elementary lipid which constituted ane molecule of glycerol and three molecules of fatty acids. Triglyceride is the storage form of lipid , which is used for energy production. Triglycerides are found circulating in the blood where they are transported by very-depression-density lipoprotein (VLDL). Triglycerides level is oftentimes estimated as lipid profiling. The elevated level of triglycerides in the blood is termed as hypertriglyceridemia. When both the level of cholesterol and triglycerides in the claret is college than the desired, this condition is called hyperlipidemia. Loftier triglyceride in the blood is associated with several risks every bit middle disease.

Desirable triglyceride level: Less than 150   mg/dL.

Borderline high: 150–199   mg/dL.

High: 200–499   mg/dL.

Very high: more than 499   mg/dL.

Rationale

Triglycerides hydrolyzed into one molecule of glycerol and 3 molecules of fatty acids by the enzyme lipase. Glycerol is phosphorylated to glycerol-3-phosphate by the enzyme glycerol kinase. The phosphate group is provided past the ATP. The glycerol-3-phosphate is oxidized to dihydroxyacetone phosphate by the enzyme glycerol-3-phosphate oxidase (GPO). Hydrogen peroxide which is formed as a by-product in the above reaction and so condensed with 4-amino antipyrine (four-AAP)/four-aminophenazone (chromogenic substrate) and 4-chlorophenol to class a red-colored quinone-imine dye. The absorbance tin can be measured at 505   nm and its intensity is directly proportional to the content of triglyceride in the sample.

$\text{Triglycerides}+{\mathrm{H}}_{\mathrm{ii}}\mathrm{O}\stackrel{\text{Lipoprotein lipase}}{\to }\begin{array}{l}\text{Glycerol}\\ +3\text{molecules of fatty acids}\end{array}$

$\text{Glycerol}+\mathrm{ATP}\stackrel{\text{Glycerol kinase}}{\to }\text{Glycerol}-\mathrm{iii}-\text{phosphate}$

$\begin{array}{l}\text{Glycerol}-3-\\ \text{phosphate}\end{array}+{\mathrm{O}}_2\stackrel{\begin{array}{c}\text{Glycerol}-3-\text{phosphatem}\\ \text{oxidase}\end{array}}{\to }\begin{array}{l}\text{Dihydroxyacetone}\\ \text{phosphate}\end{array}+{\mathrm{H}}_{\mathrm{two}}{\mathrm{O}}_2$

$\begin{array}{l}{\mathrm{H}}_{\mathrm{ii}}{\mathrm{O}}_2+4-\text{Aminoantipyrine}\\ +4-\text{Chlorophenol}\end{array}\stackrel{\text{Peroxidase}}{\to }\begin{array}{l}\text{Quinoneimine}\mathrm{dye}+{\mathrm{H}}_2\mathrm{O}\end{array}$

Materials, equipment, and reagents

A.

Reagents: Working reagent (information technology contains lipoprotein lipase, ATP, glycerol kinase, glycerol-iii-phosphate oxidase, peroxidase, 4-AAP/four-aminophenazone and 4-chlorophenol), triglyceride standard (200   mg/dL), sample.

B.

Glassware: Examination tube, pipettes, tip box, cuvette.

C.

Instruments/appliance: Spectrophotometer.

Protocols

i.

Showtime, isolate the claret and separate the serum. Store the serum at 2–8°C.

ii.

Accept three cleaned test tubes and label them as S (standard), B (bare), and T (test).

3.

Add together the reagents as shown in the table:

Reagent	Blank	Standard	Test
Sample	–	–	0.01   mL
Triglyceride standard	–	0.01   mL	–
Water	0.01   mL	–	–
Working reagent	ane   mL	1   mL	1   mL
	Mix it proceed it for 10   min at room temperature
Absorbance at 505   nm (OD505)	ODB	ODs	ODT

4.

Summate the amount of cholesterol.

Calculation

$\begin{array}{l}\text{Triglycerides}\\ \left(\mathrm{mg}/\mathrm{dL}\right)\end{array}=\frac{{\mathrm{OD}}_{\mathrm{T}}-{\mathrm{OD}}_{\mathrm{B}}}{{\mathrm{OD}}_{\mathrm{S}}-{\mathrm{OD}}_{\mathrm{B}}}\times \begin{array}{l}\text{Concentratio of standard}\\ \left(200\mathrm{mg}/\mathrm{dL}\right)\end{array}$

Safety considerations and standards

1.

Avoid hemolysis of the blood.

2.

Practice not use citrate, fluoride, and oxalate while collecting the sample.

Analysis and statistics

The amount of triglycerides in the given sample is __________mg/dL.

Pros and cons

Pros	Cons
Easy and rapid method	Interference on the action of lipase by the detergents and some drugs
No issue of low bilirubin	Expensive method
Specificity is more than than chemical methods

Culling methods/procedures

Chemical method. Liquid-phase partition method, GC-MS method, etc.

Summary

1.

The serum should be collected later 12   h of fasting.

2.

This is the enzymatic method of triglycerides estimation.

3.

In this method, the lipase enzyme hydrolyzes the triglyceride into glycerol and fatty acids. Glycerol undergoes phosphorylation then oxidation reaction in which peroxide is generated, which condenses with chromogen 4-amino antipyrine (four-AAP)/4-aminophenazone to form red-colored quinone-imine dye. The absorbance is measured at 505   nm.

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Biological macromolecules as antimicrobial agents

Md. Shahruzzaman , ... Mohammed Mizanur Rahman , in Biological Macromolecules, 2022

7.2.3 Lipid

Lipids are a chemically diverse group of biological compounds that are naturally nonpolar. They are hydrophobic but soluble in organic solvent such as alcohol, ether and chloroform. The diversity in their chemical properties has made them capable for multi-functional activeness. They perform several roles in the trunk which are very important for conveying out the biological functions of living organism. They serve equally structural materials such equally phospholipids and sterols are the major structural chemical element of biological membranes. They act equally free energy storehouse whereas fat and oil are the stored grade of energy in living organism. Furthermore, they deed every bit an insulator for plants and animals to keep them safe from the adverse surround. The three major types of lipids are triglycerides, phospholipids, and sterols.

7.2.three.1 Triglyceride

Triglyceride is the simplest lipid composed of three fatty acids that are continued with ester linkage with a glycerol unit of measurement. The main function of triglyceride is to store energy for later utilise. When any calorie more than the trunk requirement is consumed it is converted to tryglyceride and stored in fat cells. A common example of triglyceride is tristearin which is composed of 3 stearic acid attached to a molecule of glycerol. The chemical structure of triglyceride is shown in Fig. 7.5A.

Figure 7.5. Chemic structure of (A) triglyceride, (B) phospholipid, and (C) cholesterol.

7.2.3.2 Phospholipid

Phospholipid is amphiphilic chemical compound consists of a glycerol molecule containing a polar caput group and two fatty acid molecules acting as hydrophobic tail. Due to the amphiphilic property they can arrange themselves in a sure design in water to form cell membrane. Two important examples of phospholipid are phosphatidylcholine and phosphatidylserine that are institute in plasma membrane. The chemical structure of phospholipid is shown in Fig. 7.5B.

seven.two.3.3 Sterol

Sterol is different from others lipids due to its multiple ring construction. The chief office of sterol is to human action every bit hormone or intrinsic component of prison cell membrane. Cholesterol is the familiar sterol that is found in regular food items such as milk, meat, egg yolk, etc. The cholesterol is the main elective of some hormones including sex hormone. The chemical structure of cholesterol is shown in Fig. 7.5C.

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Lipids

A.S. Cole B.Sc., Ph.D. , J.Due east. Eastoe D.Sc., Ph.D., F.D.S.R.C.S., D.I.C.A.R.C.South. , in Biochemistry and Oral Biology (2d Edition), 1988

Lipids may be subdivided into

ane.

Uncomplicated lipids . These consist of long concatenation fatty acids which may be either free or combined with an alcohol by an ester linkage. They include the triglycerides (triacylglycerols) and the waxes.

2.

Compound lipids which contain additional groupings such every bit phosphoric acid, sugars, nitrogenous bases or proteins. Included in this grouping are the phospholipids, glycolipids and lipoproteins.

3.

Steroids. Although they do not oft contain fatty acids the steroids are often classed as lipids on account of their occurrence in natural fats and their solubility characteristics. They include cholesterol and the sex and adrenocortical hormones.

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Overview of Lipid Metabolism

Larry R. Engelking , in Textbook of Veterinary Physiological Chemistry (3rd Edition), 2015

•

Give examples of derived, complex and simple lipids, and talk over their physiologic differences.

•

Explicate what is meant by "the dynamic state of torso fat."

•

Dissimilarity the caloric yields of equimolar amounts of triglyceride, glycogen and protein oxidation, and explicate the differences.

•

Outline the physiologic advantage to hibernating animals of oxidizing fatty over saccharide.

•

Recognize the directly and inverse relationships betwixt lean torso mass, total trunk h2o and trunk fat content.

•

Know and sympathise the 7 primary functions of lipids.

•

Identify the atypical compound that appears to be common to all lipids, and discuss the dynamic nature of this relationship.

•

Place the intersection where carbohydrate, amino acid and lipid metabolism converge.

•

Explain why animals occupying dry environments gain an advantage past oxidizing fat.

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The Influence of Electric Fields on Biological and Model Membranes

Doncho 5. Zhelev , David Needham , in Biological Effects of Electric and Magnetic Fields, Volume 1, 1994

ii. Membrane–Membrane Contact: Natural Membranes

What almost natural membranes? Compared to the elementary lipid bilayer, natural membranes have a range of boosted ionic and molecular surface structures. The extracellular side of natural membranes, such as the red blood prison cell, is covered with a lush 1400-Å-thick layer of charged carbohydrate and protein polymers (and copolymers) that provide a steric barrier to the kind of colloidal adhesive contact that occurs for bare neutral lipid membranes. In some of our more than recent bilayer – bilayer interaction experiments, nosotros have reconstituted a model glycocalyx by incorporating bilayer-compatible lipids that are covalently linked to polyethylene glycol (PEG) moieties of 2000 g/mol molecular weight ( Needham et al., 1992a, b). Our 10-ray diffraction and micropipet experiments have shown that the 50-Å-thick layer of PEG limits interbilayer gaps to ~ 100 Å and strongly inhibits closer approach. The bilayers are not adherent at this altitude. Having characterized this grafted polymer system, we use it to assist answer some of the questions regarding the influences of distance and force on electrofusion involving glycocalyx-similar structures.

Membrane – membrane contact tin can therefore approach a maximum for bare, neutral membranes that are under the influence of van der Waals and osmotic forces of attraction, and whatsoever closer approach than 10–15 Å or so is prevented past a hydration layer. The presence of other surface structures such every bit bound polymer and charged groups serve to split agglutinative contacts, stabilize membrane-membrane interaction, and separate the lipid parts of the membranes to distances hundreds of angstrom.

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Structure and Dynamics of Membranes

G. Cevc , in Handbook of Biological Physics, 1995

one Introduction

Nature is full of barriers. Information technology was not before the germination of the first membraneous sacks that the self-replicating and catalytic molecules encapsulated in such vesicles have started to act as archaic creatures. The reason for this is that membranes present a bulwark to the free diffusion of water soluble substances and thus enforce fabric localization. The very limited diffusion of the membraneous bodies through the partly filled space plays an important role in this as well.

Primordial membranes must take emerged from the pools of ubiquitous simple lipids which take been reported to exist fifty-fifty in the interstellar space. Most lipids beingness virtually insoluble in water, they tend to form membranes spontaneously. This is true for all bones amphiphiles ¹ of the biological membranes at to the lowest degree, with the solubilities between 10⁻¹⁰ and 10⁻⁶ moles per litre. Biogenic lipids thus normally do non dissolve but rather disperse in the aqueous systems in the form of extended aggregates [i].

The most common form of the polar lipid aggregates in h2o are bilayers. These consist of ii opposing hydrocarbon monolayers separated from the surrounding water by two layers of the polar lipid headgroups. It is this membrane cadre and the ii interfaces which human activity as a diffusion barrier and/or every bit biochemical catalytic sites, depending on the type of the molecules added. Bilayers chiefly form airtight spherules, so-called liposomes, with a radius much greater than the lipid dimensions, owing to the monolayer packing constraints [2, iii]. In the thermodynamic equilibrium vesicle radii are commonly rather large, τ_five ≳ 40   nm.

But the most polar lipids are soluble in water at concentrations higher than ten⁻⁵ and upward to ten^−two moles per litre. When this solubility limit is exceeded, however, even the almost hydrophilic lipids amass spontaneously. The resulting lipid micelles normally comprise but a few dozen of molecules [5], more often than not. Micellar shape depends on the precise distribution of the polar residues on each individual molecule [4]. Most lipid micelles are spherical or disk-like (cf. fig. 1 and correspondingly modest. Their surface, consequently, is at least locally highly curved (r _{one thousand} ≤ 5 nm) and resembles the 'edge' of an open lipid bilayer.

Fig. 1. Schematic representation of various types of lipid aggregates.

Addition of large amounts of the highly water-soluble lipids to the break of less polar lipids solubilizes the closed lipid bilayer. Lipid solubilization usually gain via the formation of mixed-micelles and other types of mixed aggregates [7]. The solubilization-inducing lipids, consequently, are also chosen surfactants or detergents, to stress this fact.

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Polyketides and Other Secondary Metabolites Including Fatty Acids and Their Derivatives

Nobuyuki Hamanaka , in Comprehensive Natural Products Chemical science, 1999

1.07.2.5 Other Lipoxygenase and P450 Pathways

It is a surprising fact that the of import compounds for a living trunk are biosynthesized from simple lipids past cyclooxygenase and 5-lipoxygenase, considering in organic chemistry information technology is mutual sense that the substances which involve the divinylmethane function in a molecule are very readily oxidized past air to provide lipid peroxides (auto-oxidation). It is naturally anticipated that the interesting substances will be biosynthesized past the other pathway. In fact, a number of investigations were conducted from this point of view.

As shown in Figure 16, oxygen is introduced into positions C-5, C-8, C-9, C-xi, and C-12 in a molecule, which is presumed to be the mechanism discussed in Section 1.07.two.i

Figure xvi. Mammalian lipoxygenase pathway.

Actually, the first enzyme recognized was 12-lipoxygenase. Hamberg and Samuelsson discovered the production of a 12(S)-hydroxy-5-cis,viii-cis,x-trans,14-cis-eicosatetraenoic acrid (12-HETE) upon incubation of human being platelets with arachidonic acid. ⁶⁴ 12-HETE production suggested the presence of a lipoxygenase enzyme which oxygenated C-12 of arachidonic acid. Furthermore, Nugteren detected an enzyme with backdrop of lipoxygenase in the supernatant of broken bovine platelets, which produced 5(S)-hydroxy acrid with at to the lowest degree two cis-double bonds at the C-8 and C-11 positions. ⁶⁵ 5-Lipoxygenase catalyzes the pathway to LTs, and xi-lipoxygenase catalyzes the pathway to PG-TX as described above.

15-Lipoxygenase was constitute in rabbit reticulocytes ⁶⁶ and leukocytes. ⁶⁷ 8-Lipoxygenase ⁶⁸ was plant in mouse epidermis. However, 9-lipoxygenase has not yet been discovered. References ^69–73 are review articles dealing with mammalian lipoxygenases.

As an example, the 12-lipoxygenase pathway is shown in Figure 17. 12-Lipoxygenase has a multifunctional nature, fifty-fifty when it is purified. Namely, the oxygen function is introduced not merely at the C-12 position but as well at the C-15 position of arachidonic acid: two kinds of compounds are biosynthesized by a single enzyme. In addition, the substrate specification of these enzymes is so depression that farther oxygen function is introduced into the other positions. The murine 12-lipoxygenase of leukocyte type showed a 12/fifteen-HPETE ratio of 3 : 1, and the murine enzyme of platelet-type produced exclusively 12-HPETE.

Effigy 17. Multifunctional nature of 12-lipoxygenases.

In that location is a further complication in that 12-lipoxygenase transformed 15-HPETEs as substrates to a mixture of various dihydroperoxy and dihydroxy acids with a conjugated triene. These HPETEs were further converted by the other enzymes to a complicated mixture through xiv,15-epoxide (fourteen,xv-LTA_iv) (Figure 18). ^74–76

Figure 18. Germination, structures, and metabolism of hepoxilins.

Herein, the biosynthesis of hypoxilin, trioxilin, ^77,78 and lipoxin ⁷⁹ is shown. There are a number of isomers, which will not be discussed here. Information technology is generally considered that the physiological and pathological office of lipoxygenase products without PGs and LTs has not been conspicuously established. ^fourscore

The things that make the lipoxygenase system circuitous are not only oxidation as described to a higher place but also the lack of substrate specificity of the enzyme and oxidation with P450. The multiple catalytic activities of establish lipoxygenase accept been reviewed in detail. ⁸¹

P450 is able to act every bit a monooxygenase and catalyzes the hydroxylation or epoxidation of a variety of hydrophobic substrates. It has as well been presumed that information technology is related to the metabolism of PGs by ω-oxidation of fat acids; still, information technology is articulate that P450 forms epoxy eicosanoids by the straight addition of oxygen to the double bond of unsaturated fatty acids (Figure 19). ^82,83

Effigy xix. Structures and biosynthesis of lipoxins.

Capdevila et al. ⁸⁴ reported that handling of arachidonic acid with rat liver microsome that was pretreated with phenobarbiturate gave epoxy eicosanoids which were a mixture of cis-5,six-, 8,9-, 11,12-, and 14,xv-epoxyeicosatrienoic acids, which showed different properties from those of LT because they did not have triene office. Di-HETEs are produced by the hydrolysis of these substances (Effigy twenty).

Figure 20. Epoxidation of arachidonic acid by the P450 pathway.

Furthermore, P450 forms, likewise as the other lipoxygenases, substances in which oxygen is introduced into positions C-5, -viii, -9, -eleven, -12, and -15. Since these substances are not distinguished from the substances derived via lipoxygenase, there are some doubts nigh the physiological role of each of the HETEs. ⁸⁵

Thus, a number of eicosanoids are biosynthesized past a combination of very complex enzyme systems and nonenzymatic hydration and rearrangement reactions. It is very difficult to draw their metabolic maps. It is not until the enzymatic reactions are analyzed by the isolation and purification of each enzyme, the chemic equivalent calculated, and afterwards consideration of many newly formed optical centers, that new developments in this field are possible. Herein the substances derived via 12-lipoxygenase are shown. ⁸⁶

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Lipids, Terpenoids, and Related Substances

Theodore T. Kozlowski , Stephen One thousand. Pallardy , in Physiology of Woody Plants (Second Edition), 1997

Waxes

The waxes are esters of long-chain monohydric alcohols and longer concatenation fatty acids than those found in simple lipids, that is, with carbon chains containing more than xx carbon atoms. Waxes also incorporate alkanes with odd numbers of carbon atoms, primary alcohols, and very long-chain free fat acids.

At that place are ii kinds of leafage waxes, epicuticular and intracuticular. The epicuticular waxes comprise the outer part of the cuticle; intracuticular waxes are embedded in cutin (Stammitti et al., 1995). Wax synthesis occurs in the epidermal cells of apple fruits and several kinds of leaves, and it must occur near the site where it is deposited because of the difficulty of transporting such an insoluble material. Waxes probably are by and large synthesized in the epidermal cells equally droplets, pass out through the cell walls, and class layers on the outer surfaces. Some wax is pushed out through the cutin–wax layer, forming a deposit on the cuticle and producing the bloom characteristic of some leafage and fruit surfaces (encounter Fig. 8.iv). Waxes also occur in suberin-rich barks (Martin and Juniper, 1970). Apparently wax generally accumulates on the external surfaces of plants, in dissimilarity to suberin, which accumulates in cell walls, and to cutin, which sometimes accumulates on internal besides as external surfaces. An exception is the aggregating of liquid wax in the seeds of jojoba.

Figure 8.4. Variations in leaf waxes of broad-leaved trees: (A) American elm (× 2000), (B) white ash (× 2000), (C) saccharide maple (× 2000), and (D) eastern redbud (× 2000).

Photos by W. J. Davies.

Epicuticular waxes are physiologically important considering they restrict transpirational water loss, contribute to command of gas substitution, reduce leaching of nutrients, provide a barrier to air pollutants, and influence entry of agricultural chemicals into leaves, fruits, and stems. When present in irregular masses, waxes make leaf surfaces difficult to moisture; hence, a wetting amanuensis or "spreader" added to spray materials often ensures fifty-fifty coverage. Some of the chemicals in epicuticular wax inhibit growth of pathogenic organisms (Martin and Juniper, 1970). In some cases, however, components of leaf waxes stimulate fungal spore formation and evolution of germ tubes, thus promoting pathogenesis (Schuck, 1972).

Deposition of wax on leaves is an of import adaptation to drought. Transpiration rates of drought-tolerant plants with closed stomata commonly vary from 2 to twenty% of the rates when the stomata are open. By comparison, mesophytic plants with thinner layers of leafage waxes by and large lose from twenty to fifty% as much water with closed stomata every bit they do with open stomata (Levitt, 1980b). The permeability coefficient for diffusion of water vapor through the cuticle increased by 300 to 500 times following extraction of the cuticular wax (Schönherr, 1976), emphasizing the importance of foliage waxes in desiccation abstention by plants.

In some species, the occlusion of stomatal pores with wax profoundly reduces water loss and photosynthesis (Chapters 5 and 12). Leaf waxes in stomatal pores too increase resistance to penetration by some fungal pathogens (Patton and Johnson, 1970; Franich et al., 1977).

Some waxes are of considerable commercial importance. Among the best known is carnauba wax, obtained from the leaves of a palm, Copernicia cerifera, institute in Brazil. It contains almost 80% alkyl esters of long-chain fatty acids and 10% gratuitous monohydric alcohols. Palm wax occurs on the torso of the wax palm (Ceroxylon andicola) in layers upwardly to 2 or 3 cm in thickness. It consists of about i-third true wax, the balance being resin. Other commercial palm waxes are ouricuri wax, obtained from the Attalea palm (Attalea excelsa), and raffia wax, obtained from the dried leaves of the Madagascar raffia palm (Deuel, 1951). Eucalyptus gunnii var. acervula of Tasmania and the leaves of white sandalwood also yield wax. The leaves of Myrica carolinensis supply the fragrant wax used in bayberry candles.

Foliage waxes have been classified into two major types: (1) apartment deposits (including wax granules, rods and filaments, plates, and scales) and (ii) localized deposits (including layers and crusts as well equally liquid or soft coatings). The corporeality and structure of wax often differ between the two surfaces of the same leaf and even between different locations on the same leaf surface. For case, in Eucalyptus polyanthemos the wax was platelike over most of the leaf bract but tubular over the midrib (Hallam, 1967). The structure of leaf wax has been used as a taxonomic character to separate species of Eucalyptus and Cupressus (Hallam and Chambers, 1970; Dyson and Herbin, 1970).

The corporeality of wax on leaves varies from a trace to as much as fifteen% of the dry out weight of the leaf, and it differs with constitute species, genotype, leaf historic period, and ecology conditions. White ash leaves had thin leafage waxes; sugar maple leaves not just had thick deposits of wax, but many of the stomatal pores were occluded with wax (Kozlowski et al., 1974; Davies and Kozlowski, 1974b). Genetic variations in wax deposition take been reported in Eucalyptus and Hevea (Hairdresser and Jackson, 1957; Rao et al., 1988).

The amount of leaf wax that forms is favored by high calorie-free intensity, depression relative humidity, and drought (Baker, 1974; Weete et al., 1978). In some species, changes in leafage waxes occur in response to selection past environmental factors. In Tasmania, for example, nonglaucous (greenish) phenotypes of Eucalyptus were present in sheltered habitats and glaucous phenotypes in exposed sites. At elevations of two,000 ft (610 m) the leaves of Eucalyptus urnigera were nonglaucous and had predominantly flaky wax; at 2,300 ft (700 m) the leaf waxes consisted of flakes and rods; and at 3,200 ft (975 k) the leaves were glaucous, and their waxes consisted of masses of rodlets (Hall et al., 1965).

Waxes are produced largely during early stages of leaf expansion. Fully expanded leaves generally have lost the chapters to produce large amounts of wax. Hence, old leaves with their sparse layers of wax often accept high transpiration rates, lose large amounts of minerals past leaching, and have depression resistance to pathogens (Romberger et al., 1993).

The structure of epicuticular waxes changes during leaf development. In Douglas fir, fusion of crystalline wax rods into amorphous (solid) wax began several weeks afterward bud-break (Thijsse and Baas, 1990). An increase in the amount of solid wax occurred similarly but more slowly in 1- and two-year-onetime needles. Very immature Scotch pine needles had more amorphous wax than older needles. This ascertainment, together with the presence of wax rodlets on top of amorphous wax crusts, indicated that wax was recrystallized (Bacic et al., 1994).

The structure of leaf waxes is influenced by the mineral nutrition of plants. Proportionally more than tubular wax and less scalelike wax were produced by Douglas fir trees that were fertilized with N and K than by unfertilized copse (Chiu et al., 1992). The deteriorating effects of unbalanced mineral nutrition on coverage and structure of wax were evident in the stomatal furrows of Scotch pine needles within a year and in the epistomatal chambers a year later (Ylimartino et al., 1994). Deficiencies of Ca and Mg decreased wax coverage in both the stomatal furrows and epistomatal chambers. Coverage in the epistomatal chambers also was decreased by K deficiency and N backlog (and hence Due north:M ratios). Waxes in both the stomatal furrows and epistomatal chambers changed from tubelike to more fused and netlike structures as a issue of deficiencies of K, Mg, and Ca (and hence increased N:K, N:Mg, and Due north:Ca ratios).

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Not All Fats Are Unhealthy

Ligia J. Dominguez , Mario Barbagallo , in The Prevention of Cardiovascular Disease Through the Mediterranean Diet, 2018

3.two What Is Fat?

Dietary fat is chosen fatty of creature or plant origin used every bit nutrient. Occasionally, the term fatty is used in reference to a solid lipid at room temperature (mostly in brute foods), compared to oils that are liquid at this temperature (derived from plants). However, "fat" is a generic term that is oftentimes used as a synonym for whatsoever form of lipid. In fact, all fats have a similar chemical structure: a chain of carbon atoms bonded to hydrogen atoms. What makes one fat different from another is the length and shape of the carbon concatenation and the number of hydrogen atoms continued to the carbon atoms. Patently, slight differences in structure translate into key differences in course and part. In solid fats, saturated fatty acids predominate, while oils are predominantly unsaturated fatty acids.

The about common type of fatty is ane in which three fat acids are bound to the glycerol molecule, receiving the name of "triglycerides," which accept the shape of a small comb with merely three teeth consisting of fatty acids or a capital letter E (Fig. 3.1).

Figure 3.1. On top, schematic structure of triglycerides. Below, example of a triglyceride with three dissimilar fatty acids. One fatty acidis saturated (no double bonds) (blue), another contains 1 double bail inside the carbon chain (greenish). The third fat acid (a polyunsaturated fatty acid, blood-red) contains three double bonds within the carbon chain.

A fatty acid consists of a concatenation of carbon (4–24) and hydrogen atoms with a carboxyl grouping at the alpha finish and a methyl group at the omega end (Fig. iii.2).

Effigy 3.ii. Schematic structure of a fat acrid. A chain of carbon and hydrogen atoms with a carboxyl group at the alpha stop and a methyl group at the omega end.

Other classes of lipids are sterols (like cholesterol) and phospholipids (forming the cellular membranes).

Fats are formed from carbon, hydrogen, and oxygen, equal to carbohydrates, but the ratio betwixt hydrogen and oxygen is much higher in fats. This is what makes them more energetic than carbohydrates in accented terms. All types of fat provide the same number of calories (9   kcal/g) regardless of where they come from.

There are more than 500 types of fats, classified according to their molecular structure in unproblematic, compound, and derivatives:

•

Simple lipids : are the well-nigh abundant in the man body (approximately 95%) and in the nutrition (this form accounts for about 98% of the lipids present in food), equally triglycerides. They correspond the main class of deposit and apply.

•

Lipid compounds: triglycerides are combined with other chemic substance such as phosphorus, nitrogen, and sulfur. These compounds account for about 10% of body fatty, including phospholipids, glycolipids, and lipoproteins.

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Lipid derivatives: derived from the processing of simple or chemical compound lipids. The well-nigh important is cholesterol, but besides include vitamin D, steroid hormones, palmitic, oleic, and linoleic acids.

Phospholipids are lipids containing phosphoric acrid, present in the body and in some foods. They are part of cell membranes and diverse tissues, providing stability. Phospholipids are not particularly abundant in the diet, where they are present in animal viscera (e.g., liver, brain, and heart), and soybean and egg yolk. They are used in pregnant quantities equally emulsifying additives (lecithin, E-322, allows mixing fat and h2o) to produce margarines, cheeses and other foods.

Cholesterol is a structural component of cell membranes in the body. Furthermore, other molecules of great functional importance are manufactured from information technology, such as vitamin D, steroid hormones, and biliary acids. That is, in that location is cholesterol that our body produces naturally and another that we go from nutrient.

Cholesterol is transported in claret bound to proteins and other fats, forming the so-called lipoproteins. The best known are HDL-C (meaning High Density Lipoprotein cholesterol) or "expert cholesterol" and LDL-C (significant Low Density Lipoprotein cholesterol) or "bad cholesterol." HDL is considered good considering it leads cholesterol from peripheral cells to the liver, preventing it from building upwards in the walls of blood vessels. The dietary cholesterol is just found in brute foods, among which viscera, meats and sausages, cream and butter, pastries and cakes containing animal fat.

Fatty acids, which are the building blocks of fat are classified as saturated, monounsaturated or polyunsaturated depending on their chemical structure (Fig. 3.3).

Figure three.three. Chemic construction of a saturated (butyric), a monounsaturated (oleic), and a polyunsaturated (linoleic) fatty acrid.

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Saturated fatty acids: are free of double bonds and therefore have the maximum number of hydrogen atoms. They are found not only in animal products (sausage, butter, meat, cheese, and foam) merely also in constitute foods (coconut and palm oil).

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Unsaturated fatty acids: contain one (mono) or more (poly) double bonds between the carbon atoms and the hydrogen.

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Monounsaturated fatty acids: contain a single double bond between the carbon atoms that compose them. They are by and large found in olive oil and nuts.

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Polyunsaturated fatty acids: contain more than than 2 bonds betwixt the carbon atoms. They are contained in fish, nuts, vegetable oils (i.e., sunflower and corn) and in some plant extracts. These fats include essential and semi essential fatty acids:

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Essential fat acids, alpha linolenic, and linoleic acids: they cannot be synthesized by the human torso; are the precursors of prostaglandins, thromboxanes, and leukotrienes, substances that are involved in the function of immune system, inflammatory response, and affect the cardiovascular system (Fig. 3.four).

Figure 3.4. Chemic structure of essential fat acids: alpha-linolenic and linoleic acids.

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Semi essential fatty acids, including EPA and DHA (Fig. 3.five).

Figure 3.v. Chemical construction of omega-iii fat acids: eicosapentaenoic and docosahexaenoic.

They are called semi essential because they can derive from the biosynthetic pathway of linoleic acrid and alpha-linolenic acid, through distinct metabolic pathways, which compete for the same enzymes (Fig. 3.6).

Effigy 3.6. Metabolic pathways of linoleic acid and alpha-linolenic acid, which compete for the same enzymes biosynthetic pathways.

Particular involvement has been shown toward this category of enzymes, called desaturase, because they can exist reduced in many weather, that is, diets rich in trans fat, stress, drastic diets, malabsorption, diabetes, ionized radiation, cancer, aging, and deficiency or malabsorption of fat-soluble vitamins. Therefore, the introduction of these fatty acids (i.e., EPA and DHA from fish or fish oil) is able to bypass the trouble linked to the possible deficiency of Δ-six-desaturase. This is why fish and fish oil are considered a ameliorate source compared to oil and flaxseed, which are rich in their precursor alpha-linolenic acid. EPA and DHA are very important precursors of substances essential for the body'due south health.

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Hydrogenated fatty acids: as mentioned, usually the acids of vegetable fats are liquid at room temperature. They can be rendered solid by the hydrogenation process, which alters the chemical structure making them especially harmful for our health. They are the so-called trans-fat acids or hydrogenated fatty acids ( Fig. 3.7).

Figure iii.7. Chemic structure of a cis-fat acrid and a trans-fat acid conformation.

Triglycerides represent the form of storage of fat acids in the trunk (think of the fat accumulated in the belly and everywhere else). During the energy processes, the body provides to split the bail between glycerol and fatty acids channeling them into two completely dissimilar metabolic pathways. While glycerol is used to produce glucose, free fatty acids are transported in the bloodstream in association with albumin, a plasma protein that transports them to the muscles, where they are energy substrate for oxidative processes.

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