Lipids. *The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, which are related more by their.

lipids

*The lipids are a heterogeneous group of compounds,including fats, oils, steroids, waxes, and related compounds, which are related more by their physical than by their chemical properties. *They have the common property of being (1) relatively insoluble in water .(2) soluble in nonpolar solvents such as ether andchloroform. *Lipid is not polymers.

• Storage form of energy .• Thermal Insulation .• Protection for delicate organs .• Key component of cell membranes .• Precursors of steroid hormones as sex hormones .

Lipid Functions

1. Simple lipids: Esters of fatty acids with various alcohols.a. Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state.b. Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols.2. Complex lipids: Esters of fatty acids containing other groups in addition to an alcohol and a fatty acid.a. Phospholipids: Lipids containing, in addition to fatty acids and an alcohol, a phosphoric acid residue. They frequently have nitrogen containing bases and other substituent, eg, in glycerophospholipids the alcohol is glycerol and in sphingophospholipids the alcohol is sphingosine.

Classification of lipids

b. Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine, and carbohydrate.

c. Other complex lipids: Lipids such as sulfolipidsand aminolipids. Lipoproteins.

3 .Precursor and derived lipids: These include fatty acids, glycerol, steroids, other alcohols, lipid-soluble vitamins, and hormones.

* Acylglycerols (glycerides),cholesterol, and

cholesteryl esters (because they are uncharged ) are termed neutral lipids.

*Even chain fatty acids are common, odd chain fatty acids are rare, but 3 ‘C’ & 5 ‘c’ are common .

*Fatty acids with 14 – 20 Carbon are commonly seen in natural lipids.

* Saturated Fatty acids do not contain double bond ex. Palmitic acid. Unsaturated Fatty acids contain one or more double bonds.The double bond is always in cis configuration . One double bond – Mono Unsaturated ex. Oleic acid Two or more double bonds – Poly unsaturated fatty acids ex. Linoleic acid Linolenic acid Arachidonic acid

ESSENTIAL FATTY ACIDS : *The fatty acids which are not synthesized in the body and they should be supplied in the diet are known as Essential Fatty Acids. *All are PolyUnsaturated Fatty Acids eg.

Linoleic acid , Linolenic acid Arachidonic acid .

Fatty acid composition of three food fats. Olive oil, butter, and beef fat consist of mixtures of triacylglycerols, differing in their fatty acid composition. The melting points of these fats—and hence their physical state at room temperature (25 C)—are a direct function of their fatty acid composition. Olive oil has a high proportion of long-chain (C16 and C18) unsaturated fatty acids, which account for its liquid state at 25 C. The higher proportion of long-chain (C16 and C18) saturated fatty acids in butter increases its melting point, so butter is a soft solid at room temperature. Beef fat, with an even higher proportion of long-chain saturated fatty acids, is a hard solid

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Triacylglyerol

Fats : triglycerides which are solid at room temperature ( most saturated triglycerides, e.g. beef, fat, or lard)

Oils : triglycerides which are liquid at room temperature ( most triglycerides with several unsaturation, e.g. corn oil, peanut oil, or fish oils)

- Triacylglycerols are esters of glycerol with fatty acids . - Fats and oils that are widely distributed in both plants & animals are chemically triacylglycerols. a) SIMPLE TRIACYLGLYEROLS - All the three fatty acids are same type . b) MIXED TRIACYLGLYCEROLS Contains 2-3 different types of fatty acids , more common .

Triacylglycerols

Triglycerides

O

OH

OH

R

O

O

OH

O

R

O

R

O

O

O

R

O

R

O

OR

O

MONOGLYCERIDE DIGLYCERIDE TRIGLYCERIDE

Function: storage of energy

Structure of triglycerides

*Biological waxes are esters of long-chain (C14 to C36) saturated or unsaturated fatty acids with long-chain (C16 to C30) alcohols. * Their melting points (60 to 100 C) are generally higher than those of triacylglycerols.

* Waxes serve a diversity of other functions related to their water-repellent properties and their firm consistency.

WAXES

H3C (CH2)14 C

O

O CH2 (CH2)28-CH3

long chain alcohol

fatty acid

A honeycomb, constructed of beeswax, is firm at25C and completely impervious to water

Triacontanoylpalmitate, the major component of beeswax, is an ester of palmitic acid with the alcohol triacontanol .

* Certain skin glands of vertebrates secrete waxes to protect hair and skin and keep it pliable, lubricated and waterproof. * Birds, particularly waterfowl, secrete waxes from their preen glands to keep their feathers water-repellent. * The shiny leaves of many tropical plants are coated with a thick layer of waxes, which prevent excessive evaporation of water and protects against parasites.

* Biological waxes find a variety of applications in the pharmaceutical, cosmetic, and other industries. They are widely used in the manufacture of lotions, ointments, and polishes.

* In plankton, the free-floating microorganisms at the bottom of the food chain for marine animals waxes are the chief storage form of metabolic fuel.

- Phospholipids are compound lipids containing Glycerol ,Fatty acid ,Phosphate and other groups .Two Classes : 1-Glycerophospholipids In this group alcohol is glycerol . 2- Spingophospholipids In this group alcohol is sphingosine . Glycerophospholipids : - Glycerophospholipids Major lipids in Biological membrane . - Glycerol – 3-phosphate is esterified with 2 Fatty acids usually c1 is esterified with Saturated Fatty acid, and C2 is esterified with unsaturated fatty acid. 1. Phosphatidic acid : 1. Phosphatidic acid is simplest phospholipid .

Phospholipids

THE PRINCIPLE CLASSES OF STORAGE AND MEMBRANE LIPIDS

All these lipids have either glycerol or sphingosin as the backbone .

■The sphingolipids contain sphingosine, a long chain aliphatic amino alcohol, but no glycerol.

- Sphingomyelin has, in addition to phosphoricacid and choline, two long hydrocarbon chains,

one contributed by a fatty acid and the otherby sphingosine .

■The polar lipids, with polar heads and nonpolartails, are major components of membranes. - The most abundant are the glycerophospholipidswhich contain fatty acids esterified to two ofthe hydroxyl groups of glycerol, and a secondalcohol, the head group, esterified to the thirdhydroxyl of glycerol via a phosphodiester bond.

- Other polar lipids are the sterols. ■Glycerophospholipids differ in the structure of

their head group; common glycerophospholipidsare phosphatidylethanolamine and phosphatidylcholine. The polar heads of the glycerophospholipids carry electric charges at pH near 7.

* Glycolipids are composed of amino alcohol sphingosine + long chain fatty acid + monosaccharide unites .

* Glycolipids are important constituents of nervous tissue such as brain and the outer leaflet of the cell membrane

Cell membrane

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Steroids

* Steroid nucleus consists of four fused rings . * Sterols have steroid nucleus and a hydroxyl group

* Sterols are structural lipids present in the membranes of most eukaryotic cells.

*Cholesterol, the major sterol in animal, is both a structural component of membranes and precursor to a wide variety of steroids.

Cholesterol

Cholesterol, an amphipathic lipid, is an important component of membranes. It is the parent molecule from which all other steroids in the body, including major hormones such as the sex hormones, D vitamins,

and bile acids, are synthesized .

A B

C D1

2

3

45

6

7

8

910

11

1213

14 15

16

17

Steroid nucleus

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• Lipoproteins (blood transport molecules)• Glycoproteins (membrane structure)• Glycolipids (membrane receptors)

Combination of Biomolecules

• Lipoproteins :in membranes and transportation of materials

• Glycoproteins : antibodies, cell surface proteins

• Nucleoproteins : ribosomes

Protein Hybrids

Nucleic Acids

DNA & RNA

• Two types :• - Deoxyribonucleic acid (DNA)• - Ribonucleic acid (RNA)• Made of polymer of nucleotides joined

together by phosphodiester bond

DNA & RNA function• DNA carries and transmits the genetic

information . • RNA carry the genetic information from

nucleus to cytoplasm for protein synthesis .• RNAs are involved in most steps of gene

expression and protein biosynthesis.

Base + sugar

glycosidic bond

phosphoester bond

Nucleoside

Nucleotides

■ A nucleotide consists of a nitrogenous base (purine or pyrimidine), a pentose sugar, and one or more phosphate groups.

Nucleic acids are polymers of nucleotides, joined together by phosphodiester linkages between the 5’- hydroxyl group of one pentose and the 3’- hydroxyl group of the next.Nucleotides function as energy transfer molecules : ATP , Cyclic AMP , NAD & FAD

OH

OCH2

Sugar

H

HH

A NucleotideAdenosine Mono Phosphate (AMP)

OH

NH2

N

N N

N

BaseP

O

OH

HO OPhosphate

2’3’

4’

5’

1’Nucleotide

Nucleoside

H+

-

Pyrimidines

NH2

O

N

N NH

N

Guanine

N

N

Adenine

N

N

NH2

N O

NH2

N O

NH2

NCytosine

Purines

Uracil(RNA)CH3

N ON

O

NH

N ON

O

NH

Thymine(DNA)

Polynucleotide Formation

Dehydration reaction to form phosphodiester bond

Phosphodiester linkages in the covalent backbone of DNA and RNA. The phosphodiester bonds link successive nucleotide units. The backbone of alternating pentose and phosphate groups in both types of

nucleic acid is highly polar .

•The two strands are complementary & anti-parallel •Wound around each other in a rightward direction •stabilized by H-bonding between bases in adjacent

strands. •The bases are in the interior of the helix

•Purine bases form hydrogen bonds with pyrimidine .

DNA STRUCTURE

two polynucleotide chains are twisting around each other in the form of a double helix

Sugar phosphate backbone ofDNA

SUG

AR-PHO

SPHATE BACKBO

NE

H

P

O

HO

O

O

CH2

HOH

P

O

O

HO

O

O

CH2

H

P

O

OH

HO

O

O

CH2

NH2

N

N

N

N

O

O

NH2N

NH

N

N

N O

NH2

N

B A S E S

DNA

OH

P

O

HO

O

O

CH2

HO

O

H 2N

NHN N

N H

H

P HO

O

O

CH2

OO

N

O

H 2N

NH

H2O

H OH

P

O

HO

O

O

CH2

CH 3

O

O

HNN

H2O

5’Phosphate group

3’Hydroxyl group

5’Phosphategroup

3’Hydroxyl group

5 'C-G-A-T-T-G-C-A-A-C-G-A-T-G-C 3' | | | | | | | | | | | | | | |

3 'G-C-T-A-A-C-G-T-T-G-C-T-A-C-G 5'

Base Pair Rule •Adenine always base pairs with Thymine

(or Uracil if RNA)by two hydrogen bonds. •Cytosine always base pairs with Guanine

by Three hydrogen bonds.

NO

H

NO

N

NH Cytosine

H

O

NN

N

N

N

H

H

Guanine -+

+

+

-

-

Base PairingGuanine And Cytosine

CH3

N

O

N

ONH+

- ThymineN

NN

N

HN H

-

+Adenine

Base PairingAdenine And Thymine

Base PairingAdenine And Cytosine

NO

H

NO

N

NH Cytosine-

+

-

N

NN

N

HN

H

-

+

Adenine

Base PairingGuanine And Thymine

CH3

NO

N

O

NH+

- Thymine

H

O

NN

N

N

N

H

H

Guanine +

+

-

RNA

• Single strand of polynucleotides .• Purine bases are A & G , prymidines are C & U.

•In viruses it can carry out DNA role

*What are the differences in structure and function between DNA & RNA?