LIPIDS

-Lipids are an amphiphilic class of hydrocarbon-containing organic compounds.

-they have complicated solvation properties

-Lipid molecules have these properties because they consist largely of long hydrocarbon tails which are lipophilic in nature as well as polar headgroups (e.g. phosphate-based functionality)

-In living organisms, lipids are used for energy storage, serve as the structural components of cell membranes, and constitute important signalling molecules.

- Although the term lipid is often used as a synonym for fat, the latter is in fact a subgroup of lipids called triglycerides

Lipids

LipidsSaponified lipids

- I. Energy storing lipids: triacylgricerols or Glycerides-II.Structural lipids : waxes

phospholipids sphingolipids

non-saponifiable lipids - (poly)terpenes and derivatives

-fatty acid derivatives: prostaglandins

Fats Lipids

Saponified lipids

- Energy storing lipids: triacylgricerols: fats

Lipids

Glycerides are lipids

From a glycerol (propan-1, 2, 3-triol) core structure with one or more different fatty acyl groups (3)

these fatty acid-derived chains attached to the glycerol backbone by ester linkages

Glycerides with three acyl groups (triglycerides or neutral fats) are the main storage form of fat in animals and plants.

Saponified lipids

- Energy storing lipids: triacylgricerols: fats(glycerol + fatty acids)

Lipids

Fatty acids-Chemically, fatty acids can be described as long-chain monocarboxylic acids and have a general structure of CH3(CH2)nCOOH.

-The length of the chain usually ranges from 12 to 24, always with an even number of carbons.

-When the carbon chain contains no double bonds,it is a saturated chain.

-If it contains one or more double bonds, it is unsaturated

-The presence of double bonds generally reduces the melting point of fatty acids

-Fats contain usually saturated fatty acids

- Oils contain (poly)unsaturated fatty acids (e.g. Vegetable oils are rich in various polyunsaturated fatty acids )

- unsaturated fatty acids can occur either in cis or trans geometric isomers.

- In naturally occurring fatty acids, the double bonds are always in the cis-configuration

LipidsFat

Lipids

Fatty acids in animals: double bonds in the first half of the fatty acidsIn plants: double bonds in the second half of the fatty acids

Essential fatty acids: e.g. oleic acid (ω-9)linoleic acid (ω-6)linolenic acid (ω-3)

Only plants can produce them- double bonds in the 2nd half of the fatty acid

LipidsFat

the fatty acid oxidation is the main energy source of animalsthe oxidation number of the carbon in the fatty acids is -2The oxidation number of the carbon in the glucose „chain” is 0 When we oxidaze the carbon to CO2 (oxidation number +4)We can get more energy from fats

the fat is the most concentrated form of energy in living organisms

lipid molecules are so hydrophobe, they exclude everything – the adipose tissue contain only fat, pure substanceThe fat is stored separated from the place where E is neededThe transport of fatty acids is compicated.

the free fatty acids are highly toxic compounds

Lipids

Chemical properties

1. saponification

CH2-O-C-R1

CH-O-C-R2

CH2-O-C-R3

║

║

║

O

O

O

+ NaOHheat

CH2-OH NaO-C-R1

CH-OH + NaO-C-R2

CH2-OH NaO-C-R3

║

║

║

O

O

O

Fat

Inorganic esters

In aquaeus solutions they form micells

Amphipate molecules : likes polar and non polar as well

Detergent effect: they separate the non-polar substances from each other – cleaning effect

e.g. washing powder

Lipids

Other saponified fatty group: Inorganic esters

e.g. inorganic phospate ester : glucose 6 phosphate

Sulfate ester : ester of alcohol and sulfuric acid

R-CH2-O-S║

O

O-

O║

R-CH2-O-P║

O

O-

O-

Long carbon chain = non-polar part

Long carbon chain = non-polar part

Polar head

Polar head

Lipids

Lipids

II. Structural lipids :

1.waxes: long chain alcohols with long chain fatty acids (protection in the plant world)

2. phospholipids

Phospholipids are a class of lipids, and a major component of all biological membranes, along with glycolipids, cholesterol and proteins

2. phospholipids

Lipids

2. phospholipidsLipids

They are built upon one of a backbone:glycerol backbone, derivatives known as glycerophospholipids (or phosphoglycerides) The following components are attached to the carbons on the backbone:- a saturated fatty acid- an unsaturated fatty acid - a negatively-charged phosphate group,Which is usually attached to a nitrogen containing alcohol like ethanolamine or an organic compound such as choline.

e.g. X: -CH2-CH2-NH3+

Ethanolamine

Forming phosohatidyl ethanolamine

Lipids2. phospholipids

Phosphoglycerides are found in biological membranes, such as the cell's plasma membrane and the intracellular membranes of organelles

-Formation of lipid bilayers is an energetically-favoured process when the glycerophospholipids are in an aqueous environment. 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) (for U; 1; 2 see image before).

Lipids2. phospholipids

the non polar part:the phospholipid unsaturated carbohydrate tails are in cis coformation They can interact with each other- the membrane is more stable and they can keep the mobility of the molecules in the membrane- fluid, not rigid membrane

biological membranes

Lipids2. phospholipids

biological membranes

The fluidity of the mambrane depends on the conformation of the non polar tails ( cis) and the quality of the fatty acids:More saturated membrane, more rigid, the melting point is higherMore unsaturated membrane is more fluide , the melting point is lowerIn cold and warm periodes we have to compensate the fluidity of our membranes: in winter we need more unsaturated fatty acidsIn warm periode we need more saturated fatty acids

Lipids3. Sphingolipids

- are a class of lipids derived from the aliphatic amino alcohol sphingosine.- Sphingolipids are often found in neural tissue, and play an important role in both signal transmission and cell recognition.

The sphingosine backbone is O-linked to a (usually) charged head group such as ethanolamine or choline.The backbone is also amide-linked to an acyl group, such as a fatty acid.

Lipids3. Sphingolipids

Ceramides are the simplest type of sphingolipid.They consist simply of a fatty acid chain attached through an amide linkage to sphingosine.

R= H

Lipids3. Sphingolipids

Function

-Sphingolipids are commonly believed to protect the cell surface against harmful environmental factors by forming a mechanically stable and chemically resistant outer leaflet of the plasma membrane lipid bilayer

-Certain complex glycosphingolipids were found to be involved in specific functions, such as cell recognition and signaling.

Recently, relatively simple sphingolipid metabolites, such as ceramide and sphingosine-1-phosphate, have been shown to be important mediators in the signaling cascades involved in apoptosis, proliferation, and stress responses

Lipids4. Terpenes

Terpenes are a large and varied class of hydrocarbons, produced primarily by plantsThey are the major components of resin, and of turpentine produced from resin. The name "terpene" is derived from the word "turpentine".

When terpenes are modified chemically, such as by oxidation or rearrangement of the carbon skeleton, the resulting compounds are generally referred to as terpenoids. Terpenes and terpenoids are the primary constituents of the essential oils of many types of plants and flowers.Essential oils are used widely as natural flavor additives for food, as fragrances in perfumery, in aromatherapy, and in traditional and alternative medicines.Synthetic variations and derivatives of natural terpenes and terpenoids also greatly expand the variety of aromas used in perfumery and flavors used in food additives.

plant world: di, tri and sesqui terpens: fragrances, flavours, aromas polyterpens milks, resins

animal world: steroids (mostly free forms, sometimes esters or salts) structural and signalling functions

Lipids4. Terpenes

4. Terpenes Lipids

-Terpenes are derived biosynthetically from units of isoprene, which has the molecular formula C5H8.

-The basic molecular formulas of terpenes are multiples of that, (C5H8)n where n is the number of linked isoprene units.

-This is called the isoprene rule or the C5 rule.

- The isoprene units may be linked together "head to tail" to form linear chains or they may be arranged to form rings.

Isoprene unit

As chains of isoprene units are built up, the resulting terpenes are classified sequentially by size as hemiterpenes, monoterpenes, sesquiterpenes, diterpenes, sesterterpenes, triterpenes, and tetraterpenes.

Lipids4. Terpenes

Hemiterpenes consist of a single isoprene unit. Isoprene itself is considered the only hemiterpeneMonoterpenes consist of two isoprene units and have the molecular formula C10H16. Sesquiterpenes consist of three isoprene units and have the molecular formula C15H24

The sesqui- prefix means one and a half. Diterpenes are composed for four isoprene units and have the molecular formula C20H32. Examples: taxadiene (precursor of taxol). Diterpenes also form the basis for biologically important compounds such as retinol, retinal, and phytol. Sesterterpenes, terpenes having 25 carbons and five isoprene units, are rare relative to the other sizes. The sester- prefix means half to three, i.e. two and a half. Triterpenes consist of six isoprene units and have the molecular formula C30H48.

Tetraterpenes contain eight isoprene units and have the molecular formula C40H56. Biologically important tetraterpenes include the acyclic lycopene, the monocyclic gamma-carotene, and the bicyclic alpha- and beta-carotenes

Polyterpenes consist of long chains of many isoprene units.

4. Terpenes Lipids

Polyterpenes consist of long chains of many isoprene units.Sterane sceletons

e.g. Cholesterol

Sterane sceleton + -OH

Cholesterol is a sterol (a combination steroid and alcohol), a lipid found in the cell membranes of all body tissues, and is transported in the blood plasma of all animalsIts level in blood can be raised beyond natural levels by eating food in excess of daily requirements, especially with cholesterol-containing foods.

Cholesterol plays a central role in many biochemical processes, but is best known for the association of cardiovascular disease with various lipoprotein cholesterol transport patterns and high levels of cholesterol in the blood. Cholesterol is insoluble in blood, but is transported in the circulatory system bound to one of the varieties of lipoprotein, spherical particles which have an exterior composed mainly of water-soluble proteins.

4. Terpenes Lipids

Steroid hormons: different substituent on the sterane sceleton

e.g. aldosteron testosteron progesteron

testosteroneprogesterone