Medical chemistry (2)Part II (Lipids)

week 5 lectures1435-36

Glycerides ,Non-glyceride lipidsMembranes Lipids

Taif UniversityCollege of Medicine

Preparatory Year Students

Lectures outlines

Definition and importance of lipids

Classification of lipids

Fatty acids structure and properties

Important reactions of FA

Glycerides

Non-glyceride lipids

Membranes Lipids

Phospho-glycerides

Phospho-glycerides

A glycerophospholipid is a lipid that contains two fatty acids and a phosphate group esterified to a glycerol molecule and an alcohol esterified to the phosphate group.

Glycerophospholipids

Phosphatidyl ester

Phosphatidyl ethanolamine(cephalin)

Phosphatidyl choline(lecithin-emulsifier)

Phosphatidyl serine

Phospho-glyceridesPhosphoLipids

inositol

The Importance and functions of phospholipids are :

1- Amphipathic molecules they form micelles in water.

2- Good emulsifying factors.3- Lung surfactant mainly of dipalmitoyl-lecithin, the lack of which is responsible for respiratory distress syndrome

in premature infants.

4- Prevent deposition of cholesterol (biliary calculi).5- Constituents of lipid bilayer in cell membranes6- Provide arachidonic acid for synthesis of

eicosanoids.7- Essential for blood clotting, as they provide the

platelet activating factor (PAF)

Lipids Classification

Eicosanoides

Nonglyceride Lipids A- Sphingolipids

Sphingolipids are derivatives of ceramide (an amide between a fatty acid and sphingosine) and an amino alcohol.

Ceramide Structure

Sphingolipids

Sphingophospholipids(Sphingomyelins )

Sphingoglycolipids(Cerebrosides &

Gangliosides)

Sphingomyelins

Fatty acid

Phosphate groupCholine

• present in cell membranes specially of the lungs and brain mainly in the myelin sheath

. It contains sphingosine (sphingol) which is 18 carbon amino alcohol fatty acids are linked to sphingosine to form ceramide, which is connected to phoshocholine to form sphingomyelin.

Sphingoglycolipids

are carbohydrate-containing ceramide derivatives (in the outer face of plasma membranes)

Glycosphingolipids at the cell surface are sites of recognition.They found mainly in the myelin sheath and cell membrane of RBCs. They act as cell membrane receptors for hormones and external stimuli. They provide recognition properties.

Cerebrosides(Monosaccharide)

Gangliosides(Oligosaccharide)

Nonglyceride Lipids

Gangliosides

Oligosaccharide linked to ceramide

Example:blood group

identification

Glucocerebrosides occur in the plasma membrane of non-neuronal cells

Galactocerebrosides occur in the plasma membrane of neurons

Cerebrosides

Nonglyceride Lipids: B-Steroids

CholesterolCholesterol is a C27 steroid molecule that is:

a component of cell membranesa precursor for other steroid-based lipids:

bile acidssteroid hormonesVitamin D3 (cholecalciferol) Blood level of cholesterol: ranging from 100 to 200 mg/dL (30% as free cholesterol and 70% as cholesteryl esters) Hazards of hyperchosterolemia: Increased plasma level of cholesterol predisposes to atherosclerosis and coronary heart diseases.

Steroid Hormones• Are Oxidized

cholesterol derivatives

• Function as:• sex hormones• metabolic

regulation• Anti-

inflammatory compounds

glucose metabolism,salt excretion (adrenalgland)

female sex hormone(ovaries, placenta)

male sex hormone (testis

antiinflammatory compounds

Bile acids• A bile acid is a cholesterol derivative that

functions as a lipid-emulsifying agent in the aqueous environment of the digestive tract.

• Obtained by oxidation of cholesterolFunctions: • Conversion of cholesterol

to bile salt is an important mechanism for removal of excess cholesterol from blood.

• prevent precipitation of cholesterol  

• They are good emulsifying factors important for digestion and absorption of fats.

Lipids Classification

Eicosanoides

Nonglyceride Lipids C) Waxes

• Are esters of long-chain fatty acids with long-chain alcohols (a very high melting point)

Example:Triaconoylpalmitate,a major component of bees wax

Functions:•energy stores•water-repellent

Nonglyceride Lipids : D-Eicosanoids Eicosanoids are important regulatory molecules Referred to as local regulators (Function where they are

produced). Three classes: Prostaglandins, Thromboxanes, and

Leukotrienes Prostaglandins – mediate pains sensitivity, inflammation

and swelling Thromboxanes – involved in blood clotting, constriction

of arteries Leukotrienes – attract white cells, involved

inflammatory diseases (asthma, arthritis, etc..)

ProstaglandinsProstaglandins have:20 carbon atoms in their fatty acid chains.An OH on carbon 11 and 15.A trans double bond at carbon 13.

Prostaglandins in the BodyProstaglandins are:

• Produced by injured tissues.

• Involved in pain, fever, and inflammation.

• Not produced when anti-inflammatory drugs such as aspirin inhibit their synthesis.

For more information about prostaglandins please visit:

http://www.elmhurst.edu/~chm/vchembook/555prostagland.html

Biomembranes

Biomembranes

Lipid Structure

• Hydrophilic head – H2O loving – due to polar group in the head

• Hydrophobic tail – H2O hating – due to the long hydrocarbon tails

Membrane Lipidshy

drop

hobi

c fa

tty

acid

tail

hydrophilic head

General characteristics of membrane lipids

Structure of phospholipids

hydr

opho

bic

fatt

y ac

id c

hain

s

hydrophilic head

Membrane Lipids

A space-filling model of a typical phospholipid bilayer

Because their fatty acid tails are poorly soluble in water, phospholipids spontaneously form bilayers in aqueous solutions, with the hydrophobic tails buried in the interior of the membrane and the polar head groups exposed on both sides, in contact with water

Important Classes of Lipids

Glycerol backbone Sphingosine backbone

Question

To which class of lipids belong the following molecules?

A B C

D E F

G H