lipids

Question 1

lipids

Answer 1

The lipids are a heterogeneous group of compounds related to fatty acids and include fats, oils, waxes and other related substances.
These are oily or greasy organic substances, relatively insoluble in water, and considerably soluble in organic solvents like ether, chloroform and benzene.
The term ‘lipid’ was first used by the German biochemist Bloor in 1943 for a major class of tissue components and foodstuffs.

Question 2

function/importance of lipids

Answer 2

-Storage form of energy (triacylglycerol)
-Structural components of biomembranes (phospholipids and cholesterol)
-Metabolic regulators (steroid hormones and prostaglandins)
-Act as surfactants, detergents and emulsifying agents (amphipathic lipids)
-Act as electric insulators in neurons
-Provide insulation against changes in external temperature (subcutaneous fat)
-Give shape and contour to the body
-Protect internal organs by providing a cushioning effect (pads of fat)
-Help in absorption of fat soluble vitamins (A, D, E and K)
-Improve taste and palatability of food.

Question 3

classification of lipids based on their chemical composition.

Answer 3

simple lipids
compound lipids
derived lipids

Question 4

simple lipids

Answer 4

Simple lipids: These are esters of fatty acids with various alcohols.
- Neutral Fats (Triacylglycerol, TAG):
These are esters of fatty acids with trihydroxy alcohol, glycerol. Oils are fats in the liquid state.
- Waxes:
These are esters of fatty acids with higher molecular weight monohydric alcohols.

Question 5

compound lipids

Answer 5

Compound lipids: These are esters of fatty acids with alcohol and possess additional group(s) also.
- Phospholipids:
These are lipids containing, in addition to fatty acids and glycerol, a phosphoric acid, a nitrogen base and other substituents. For example, in glycerophospholipids the alcohol is glycerol and in sphingophospholipids, the alcohol is sphingosine.
- Glycolipids:
These are lipids containing a fatty acid, sphingosine, and carbohydrate.

Question 6

derived lipids

Answer 6

Derived Lipids: These are compounds obtained by hydrolysis of simple of compound lipids. These include fatty acids, alcohols, mono- and diglycerides, steroids, terpenes and carotenoids.
Glycerides and cholesterol esters, because of their uncharged nature, are also called neutral lipids.

Question 7

classification based on particular chemical reaction (Saponification) that lipids undergo.

Answer 7

Saponification refers to the process in which esters are hydrolyzed under basic conditions.

Saponifiable Lipids
-Saponifiable lipids are esters that undergo hydrolysis in basic solution to yield two or more smaller product molecules.
-Triglycerides, waxes, phospholipids, and sphingolipids are all belong to this class.

non-saponifiable lipids
-Nonsaponifiable lipids are not esters and cannot be hydrolyzed into smaller components.
-Steroids and prostaglandins belong to this class.

Question 8

chemistry of fatty acids

Answer 8

Fatty acids are long, unbranched hydrocarbon chains with a carboxylic acid group at one end.
It is represented by a chemical formula R-COOH, where R stands for hydrocarbon chain.
Fatty acids are amphipathic compounds because the carboxyl group is hydrophilic and the hydrocarbon tail is hydrophobic.
The carboxyl group can ionize as the carboxylate anion (–COO- ) under the proper conditions of physiological pH.

Question 9

micelles

Answer 9

In aqueous solution, the ions of fatty acids associate to form spherical clusters, called micelles.
In micelles, the nonpolar chains extend toward the interior of the structure away from water, and the polar carboxylate groups face outward in contact with the water.

Question 10

charcteristics of fatty acids

Answer 10

The fatty acids found in natural lipids have several characteristics in common:
They are usually straight-chain carboxylic acids (no branching).
The sizes of most common fatty acids range from 10 to 20 carbons.
Fatty acids usually have an even number of carbon atoms (including the carboxyl group carbon).
Fatty acids can be saturated (containing no double bonds between carbons) or unsaturated (containing one or more double bonds between carbons).
In terms of carbon chain length, fatty acids are characterized as:
-Long-chain fatty acids (C12 to C26),
-Medium chain fatty acids (C8 and C10), or
-Short-chain fatty acids (C4 and C6).
Fatty acids are rarely found free in nature but rather occur as part of the structure of more complex lipid molecules.

Question 11

classification of fatty acids

Answer 11

The hydrocarbon chain of a fatty acid may or may not contain carbon–carbon double bonds.
On the basis of this consideration, fatty acids are classified as:
1- Saturated fatty acids (SFAs),
2- Unsaturated Fatty Acids
3- Monounsaturated fatty acids (MUFAs), and
4- Polyunsaturated fatty acids (PUFAs).

Question 12

saturated fatty acid

Answer 12

A saturated fatty acid is a fatty acid with a carbon chain in which all carbon–carbon bonds are single bonds.
Examples include:
- Propionic acid
- Palmitic acid
- Stearic acid

Question 13

unsaturated fatty acids

Answer 13

Unsaturated Fatty Acids
They are classified further according to degree of unsaturation.
- Monounsaturated Fatty Acids (MUFA’s)
- Polyunsaturated Fatty Acids (PUFA’s)

Question 14

monounsaturated fatty acid

Answer 14

Monounsaturated Fatty Acids
A monounsaturated fatty acid is a fatty acid with a carbon chain in which one carbon–carbon double bond is present.
For example, Oleic acid is a monounsaturated fatty acid, that is found in nearly all fats.

Question 15

polyunsaturated fatty acids

Answer 15

Polyunsaturated Fatty Acids
A polyunsaturated fatty acid is a fatty acid with a carbon chain in which two or more carbon–carbon double bonds are present.
Up to six double bonds are found in biochemically important PUFAs; they include:
-Dienoic acids series have two double bonds, e.g. linoleic acid
-Trienoic acids series have three double bonds, e.g. linolenic acid
-Tetraenoic acid series with four double bonds, e.g. arachidonic ac

Question 16

nomenclature of fatty acids

Answer 16

The systematic nomenclature of the fatty acids is based on the Genevan system.
According to this system, the fatty acid is named after the hydrocarbon with the same number of carbon atoms.
The suffix -oic is written in place of the final letter e in the name of the hydrocarbon.
The names of saturated fatty acids end with the suffix –anoic e.g., Octadecanoic acid.
The names of unsaturated fatty acids end with the suffix –enoic e.g., Octadecenoic acid (Oleic acid).

Question 17

important saturated fatty acids

Answer 17

Common Name
Structural Notation
Formula
Common Sources

Lauric Acid
12:0
CH3(CH2)10COOH
Laurel oil, Spermaceti

Myristic Acid
14:0
CH3(CH2)12COOH
Butter and wool fat

Palmitic Acid
16:0
CH3(CH2)14COOH
Palm Oil
Stearic Acid

18:0
CH3(CH2)16COOH
Animal and plant fats

Arachidic Acid
20:0
CH3(CH2)18COOH
Peanut Oil

Question 18

common unsaturated fatty acids

Answer 18

Common Name
Structural Notation
Formula
Common Sources

Oleic Acid
18:1 – Δ9
CH3(CH2)7CH=CH(CH2)7COOH
Animal and plant fats

Linoleic Acid
18:2 – Δ9,12
CH3(CH2)4CH=CH(CH2)CH=CH(CH2)7COOH
Peanut & cottonseed Oil

Linolenic Acid
18:3 – Δ9,12,15
CH3(CH2CH=CH)3(CH2)7COOH
Linseed Oil

Arachidonic Acid
20:4 – Δ5,8,11,14
CH3 (CH2)4(CH=CHCH2) 4(CH2)2COOH
Animal fats

Question 19

isomersim in fatty acid

Answer 19

The unsaturated fatty acids exhibit geometric (or cis-trans) isomerism at the double bonds.
In biochemically important MUFAs, the configuration about the double bond is nearly always cis rather than trans.
‘Cis’ form is comparatively unstable and is more reactive.
For example, Oleic acid can exist in two forms: cis-oleic acid and trans-oleic acid which is also called elaidic acid.
‘Cis’ configuration creates a rigid 30o bend, or kink, in the fatty acid chain that is not found in saturated fatty acids.
Such a bend affects the physical properties of a fatty acid.

Question 20

essential faty acids

Answer 20

Essential fatty acids are those polyunsaturated fatty acids that cannot be synthesized by our cells and we should obtain them from plants through diet.
Linoleic acid and linolenic acid are the only essential fatty acids for animals.
Other polyunsaturated fatty acids can be synthesized from these essential fatty acids.
For example, arachidonic acid can be synthesized only from linoleic acid.
Therefore, in deficiency of linoleic acid, arachidonic acid also becomes an essential fatty acids.

Question 21

importance of essential fatty acid

Answer 21

Linoleic acid is the starting material for the biosynthesis of arachidonic acid.
Arachidonic acid is the major starting material for eicosanoids, substances that help regulate blood pressure, clotting, and several other important body functions.
Linolenic acid is the starting material for the biosynthesis of two additional omega-3 fatty acids.
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are important constituents of the communication membranes of the brain and are necessary for normal brain development.
EPA and DHA are also active in the retina of the eye.

Question 22

neutral fats

Answer 22

Triacylglycerol, also called triglycerides, are composed of three fatty acids bonded by an ester linkage to glycerol.

Triacylglycerol are of two types:
1- Simple Triacylglycerol
2Triacylglycerol are of two types:
Simple Triacylglycerol
Mixed Triacylglycerol
Naturally occurring simple triacylglycerols are rare.
Most biochemically important triacylglycerols are mixed triacylglycerols.

Question 23

simple triacyglycerol

Answer 23

These types of triacylglycerol contain the same types of fatty acids at the three carbon atoms.
The triacylglycerol produced from glycerol and three molecules of stearic acid is an example of a simple triacylglycerol.

Question 24

mixed triacylglycerol

Answer 24

Mixed Triacylglycerol
These types of triacylglycerol contain more than one kind of fatty acid molecule.
Figure shows the structure of a mixed triacylglycerol in which one fatty acid is saturated, another monounsaturated, and the third polyunsaturated.

Question 25

fats

Answer 25

A fat is a triacylglycerol mixture that is a solid or a semi-solid at room temperature (25◦C).
Generally, fats are obtained from animal sources.
All fats, even highly saturated fats, contain some unsaturated fatty acids.

Question 26

oil

Answer 26

An oil is a triacylglycerol mixture that is a liquid at room temperature (25 ◦C).
Generally, oils are obtained from plant sources.
All oils, even polyunsaturated oils, contain some saturated fatty acids.

Question 27

REACTIONS OF TRIACYLGLYCEROLS
-hydrolysis

Answer 27

Fats can be hydrolyzed in the presence of an acid or a base.
Under acidic conditions, the hydrolysis products are glycerol and fatty acids.
Under basic conditions, the hydrolysis products are glycerol and fatty acid salts.
Within the human body, triacylglycerol hydrolysis occurs during the process of digestion by the specific fat-splitting enzymes called lipases, for example pancreatic lipase.
Triacylglycerol is sequentially hydrolyzed to diacylglycerol and monoacylglycerol and finally glycerol plus 3 fatty acids.

Question 28

REACTIONS OF TRIACYLGLYCEROLS-saponification

Answer 28

Hydrolysis of a fat by an alkali such as sodium hydroxide or potassium hydroxide is called saponification.
For fats and oils, the products of saponification are glycerol and fatty acid salts.

Question 29

REACTIONS OF TRIAC REACTIONS OF- hydrogenation

Answer 29

Hydrogenation involves hydrogen addition across carbon–carbon double bonds, which increases the degree of saturation as some double bonds are converted to single bonds.
Many food products are produced via partial hydrogenation.
In partial hydrogenation some, but not all, of the double bonds present are converted into single bonds.
In this manner, liquids (usually plant oils) are converted into semi-solid materials.
This is the basis of Banaspati (Dalda) manufacture, where inedible and cheap oils like cotton seed oil are hydrogenated and converted to edible solid fat.

Question 30

REACTIONS OF TRIACYLGLYCEROLS- oxidation

Answer 30

Fats very rich in unsaturated fatty acids such as linseed oil undergo spontaneous oxidation at the double bond forming aldehyde and carboxylic acid products.
The short-chain aldehydes and carboxylic acids so produced often have objectionable odors, and fats and oils containing them are said to have become rancid.
To avoid this unwanted oxidation process, commercially prepared foods containing fats and oils always contain antioxidants.
Two naturally occurring antioxidants are vitamin C and vitamin E.

Question 31

REACTIONS OF TRIACYLGLYCEROLS- rancidity

Answer 31

The unpleasant taste and odor developed by most natural fats on aging is refereed to as rancidity.
Hydrolytic rancidity is due to partial hydrolysis of the fats due to traces of hydrolytic enzymes present in naturally occurring fats and oils.
Oxidative rancidity is the result of partial oxidation of unsaturated fatty acids with resultant formation of epoxides and peroxides of small molecular weight fatty acids by peroxides and free radicals.
The same process, if it occurs in vivo will affect the integrity of biomembranes, leading to cell death.

Question 32

fat constants

Answer 32

Fat constants or numbers are test necessary to:
-Identify a pure fat
-Assess the degree of adulteration
-Determine the proportions of different types of fat in a mixture

Question 33

saponification number

Answer 33

Saponification Number
Saponification number is defined as the number of milligrams of potassium hydroxide required to saponify one gram of fat.
It is inversely proportional to the molecular weight of fat.
This value is high in fats containing a short chain fatty acids.
For example, the saponification number of:
Butter = 220
Coconut oil = 260

Question 34

acid number

Answer 34

Acid Number
Acid number is the number of milligrams of KOH required to neutralize the free fatty acids present in one gram of fat.
It is used for the detection of hydrolytic rancidity because it measures the amount of free fatty acids present.
Acid number is directly proportional to the rancidity.

Question 35

iodine number

Answer 35

Iodine Number
Iodine number is the number of grams of iodine absorbed by 100 grams of fat.
It is an index of the degree of unsaturation and is directly proportional to the content of unsaturated fatty acids.
Higher the iodine number, higher is the degree of unsaturation, e.g.
Butter = 28,
Sunflower oil = 130

Question 36

acetyl number

Answer 36

Acetyl Number
Acetyl number is the number of milligrams of KOH needed to neutralize the acetic acid liberated from hydrolysis of 1gm of acetylated fat.
The natural fat that contains fatty acids with free hydroxyl groups are converted into acetylated fat by reaction with acetic anhydride.
Thus, acetyl number is a measure of the amount of hydroxy fatty acids in fat content.
Castor oil because of its high content of ricinoleic acid has a high acetyl number.
Acetyl number of some oils are:
Castor oil = 146-150
Cod Liver oil = 1.1
Cotton Seed oil = 21-25
Olive oil = 10.5

Question 37

reichert meissi number

Answer 37

Reichert Meissl Number
Reichert-Meissl number is the numbers of milliliters of 0.1N alkali required to neutralize the volatile acid obtained from 5g of a fat, which has been saponified then acidified to liberate the fatty acids and then steam distilled.
It is also known as volatile fatty acid number.
Reichert Meissl value for:
Butter = 26
Coconut oil = 7.
it is less than one for other edible oils.
The admixture of certain fats may be used to prepare synthetic butter which may simulate butter in most of the constants except RM value and hence, can be detected.

Question 38

waxes

Answer 38

Waxes are esters of long-chain saturated and unsaturated fatty acids with long-chain monohydroxy alcohols.
The fatty acids range in between C14 and C36 and the alcohols range from C16 to C36.
Beeswax, for example, contains a wax (1-triacontyl palmitate) with the following structure:

Question 39

charceristics/ functions of waxes

Answer 39

Waxes generally have higher melting points than fats (60 to 100°C) and are harder.
Animals and plants often use them for protective coatings.
In plants, waxes are secreted as surface coating to prevent excessive evaporation and to protect against parasites.
In animals, waxes are secreted by cutaneous glands as a protective coating to keep the skin pliable, lubricated and water-proof.
important waxes include carnauba wax (from a Brazilian palm tree), lanolin (from lamb’s wool), beeswax, and spermaceti (from whales).
These substances are used to make cosmetics, polishes, candles, and ointments.
Sperm whale wax (spermaceti) and beeswax are composed mainly of palmitic acid esterified with either hexacosanol, CH3(CH2)24.CH2OH or triacontanol, CH3(CH2)28.CH2OH.

Question 40

phospholipids

Answer 40

Phospholipids are the most abundant membrane lipids.
They serve primarily as structural components of membranes and are never stored in large quantities.
They differ from triglycerides in possessing usually one hydrophilic polar “head” group and usually two hydrophobic nonpolar “tails”.
For this reason, they are often called polar lipids.

Question 41

classes of phospolipids

Answer 41

There are two classes of phospholipids:
1- Glycerophospholipids or Phosphoglycerides
2- Sphingophospholipids or Phosphosphingosides

Question 42

glycerphospholipids

Answer 42

Glycerophospholipids
In these compounds, glycerol is linked by ester bonds to two fatty acids and one phosphate, which in turn is linked by ester bond to another alcohol (usually amino alcohol).
Phosphoglycerides serve as a major component of cell membranes
The alcohol attached to the phosphate group in a phosphoglyceride is usually one of three amino alcohols: choline, ethanolamine, or serine.

Question 43

lecithins

Answer 43

Phosphatidylcholines are also known as lecithins.
Various oil seeds like soybean and the yeasts are important sources from plant world.
In animals, they are distributed in liver, brain, nerve tissues, sperm and egg yolk.
Dipalmitoyl lecithin is an important phosphatidylcholine found in lungs, secreted by pulmonary type II epithelial cell.
It acts as a lung surfactant and is necessary for normal lung function.
It reduces surface tension in the alveoli, thereby prevents alveolar collapse.

Question 44

cephalins

Answer 44

Phosphatidylethanolamines and phosphatidylserines are also known as cephalins.
Phosphoglycerides in which the alcohol is ethanolamine or serine, rather than choline, are called cephalins.
These compounds are found in heart and liver tissue and in high concentrations in the brain.
They are also found in blood platelets, where they play an important role in the blood-clotting process.

Question 45

inositol

Answer 45

Another important group of glycerophospholipids is the phosphatidylinositols (PI), in which the alcohol is inositol.
In phosphatidylinositol, inositol is present as the stereoisomer myoinositol.
Phosphatidylinositols in their higher phosphorylated form, such as phosphatidylinositol 4,5-bisphosphates (PIP2), serve as signaling molecules in chemical communication.

Question 46

plasmalogens

Answer 46

Plasmalogens constitute about 10% of the phospholipids of the brain and muscle.
Structurally, these resemble lecithins and cephalins but have one of the fatty acids replaced by an unsaturated ether.
These are found in myelin and in cardiac muscle.
Plasmalogen is a platelet activating factor (PAF) and involved in platelet aggregation and degranulation.

Question 47

cardiolipin

Answer 47

Cardiolipin
Cardiolipins are present in abundance in inner mitochondrial membranes, and their complete hydrolysis yields:
Four molecules of fatty acids
Three glycerol molecules
Two phosphate ions

Question 48

phosphosphingosides

Answer 48

Phosphosphingosides
A phosphosphingosides is a lipid that contains one fatty acid and one phosphate group attached to a sphingosine molecule and an alcohol attached to the phosphate group.
All phospholipids derived from sphingosine have:
-the fatty acid attached to the sphingosine —NH2 group via an amide linkage,
-the phosphate group attached to the sphingosine terminal —OH group via an ester linkage, and
-an additional alcohol esterified to the phosphate group.
Sphingophospholipids in which the alcohol esterified to the phosphate group is choline are called sphingomyelins.
Sphingomyelins are found in all cell membranes and are important structural components of the myelin sheath.

Question 49

glycolipid

Answer 49

a complex lipid that contains both a fatty acid and a carbohydrate component attached to a sphingosine molecule.

Question 50

cerebrosides

Answer 50

Cerebrosides are the simplest sphingoglycolipid that contain a single monosaccharide unit—either glucose or galactose and named as glucocerebrosides and galactocerebrosides.
Cerebrosides are present in high concentrations in the white matter of the brain as well as in myelin sheathes.

Question 51

types of cereberosides

Answer 51

Four types of cerebrosides have been characterized, depending upon the type of fatty acids they contain.
-Kerasin−contains saturated C 24 lignoceric acid.
-Phrenosin (cerebron)−contains a 2-hydroxy derivative of lignoceric acid called cerebronic acid.
-Nervon−contains an unsaturated homologue of lignoceric acid called nervonic acid,
-Oxynervon−contains a 2-hydroxy derivative of nervonic acid called oxynervonic acid

Question 52

ganliosides

Answer 52

Gangliosides are more complex glycolipids that contain a branched chain of up to seven monosaccharide residues.
Gangliosides also generally contain sialic acid, which is usually N-acetylneuraminic acid (NANA) attached to ceramide (N-acylsphingosine).
These substances occur in the gray matter of the brain as well as in the myelin sheath.
Several types of gangliosides such as GM1, GM2, GM3, etc. have been isolated from brain and other tissues.
The simplest ganglioside found in tissues is GM3.

Question 53

derived lipids

Answer 53

Unsponifiable compounds obtained by hydrolysis of simple or compound lipids are called derived lipids.
Derived lipids include prostaglandins and related compounds, fat soluble vitamins and steroids.

Question 54

eicosanoids

Answer 54

Eicosanoids are the compounds derived from arachidonic acid that function as messenger lipids.
There are three principal types of eicosanoids:
Prostaglandins
Leukotrienes
Thromboxanes

Question 55

prostaglandins

Answer 55

Prostaglandins were first detected in the seminal fluid, which is produced by the prostate gland and hence the name.
Chemically, they are considered to be derived from 20C cyclic saturated fatty acid, prostanoic acid.

Question 56

functionf of prostaglandins

Answer 56

Some of the functions of prostaglandins are:
Control of blood pressure
Stimulation of smooth muscle contraction
Induction of inflammation
Inhibition of platelet aggregation

Question 57

Leukotrienes

Answer 57

Leukotrienes are compounds that, like prostaglandins, are derived from arachidonic acid.
They are found in leukocytes (white blood cells) and have three conjugated double bonds; these two facts account for the name.

Question 58

functions of leukotrienes

Answer 58

Various inflammatory and hypersensitivity (allergy) responses are associated with elevated levels of leukotrienes.
Leukotriene C produce long-lasting muscle contractions, especially in the lungs, and can cause asthma-like attacks.
One way to counteract the effects of leukotrienes is to inhibit their uptake by leukotriene receptors (LTRs) in the body.
A new antagonist of LTRs, zafirlukast, is used to treat and control chronic asthma.

Question 59

thromboxanes

Answer 59

Thromboxanes contain cyclic ethers as part of their structures.
These compounds were called thromboxanes because they were first isolated from thrombocytes.
The most widely studied member of the group, thromboxane A2 (TxA2), is known to induce platelet aggregation and smooth-muscle contraction.

Question 60

steroids

Answer 60

Steroids are a group of compounds that contain cyclopentanoperhydrophenanthrene ring structure.
This ring is present in steroid hormones, bile acids, cholesterol etc.

Question 61

cholestrol

Answer 61

Cholesterol is a C27 steroid molecule that is a component of cell membranes and a precursor for other steroid-based lipids.
Cholesterol is amphipathic, with a:
Polar head, the hydroxyl group at C3 and a
Nonpolar the steroid nucleus and hydrocarbon side chain at C17.
Most of the cholesterol in the body exists as a cholesterol ester, with a fatty acid attached to the hydroxyl group at C3.

Question 62

functions of cholestrol

Answer 62

Cholesterol is widely distributed in all the cells of the body but particularly in nervous tissue.
It is synthesized in our body as well as supplied in the diet.
Cholesterol serves as the precursor for a variety of biologically important products, including: steroid hormones, bile acids and fat soluble vitamins.
It is a major structural constituent of the cell membranes and plasma lipoprotein

Question 63

bile acids

Answer 63

A bile acid is a cholesterol derivative that functions as a lipid-emulsifying agent in the aqueous environment of the digestive tract.
Approximately one-third of the daily production of cholesterol by the liver is converted to bile acids.

Question 64

bile acids chemistry

Answer 64

Obtained by oxidation of cholesterol, bile acids differ structurally from cholesterol in three respects:
They are tri- or dihydroxy cholesterol derivatives.
The carbon 17 side chain of cholesterol has been oxidized to a carboxylic acid.
The oxidized acid side chain is bonded to an amino acid (either glycine or taurine) through an amide linkage.
The presence of this amino acid attachment increases both the polarity of the bile acid and its water solubility.

Question 65

types of bile acids

Answer 65

The three major types of bile acids produced from cholesterol by biochemical oxidation are:
Cholic acid,
7-deoxycholic acid, and
12-deoxycholic acid.