bio.lesson document 6

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BIO 203 Biochemistry I bySeyhun YURDUGÜL,Ph.D.

Lecture 7

Lipids



C

ontent Outline� Major roles of biological lipids

� Fatty acids� Triacylglycerides

� Plasmalogens

� Sphingolipids



Major roles of biological lipids

� Biological molecules,

� that are insoluble in aqueous solutions;

� and soluble in organic solvents:

� are classified as lipids.



Major roles of biological lipids

� The lipids of physiological importance for humanshave four major functions:

� 1. serve as structural components of biologicalmembranes.� 2. provide energy reserves, predominantly in the

form of triacylglycerols.

� 3. Both lipids and lipid derivatives serve asvitamins and hormones.

� 4. Lipophilic bile acids aid in lipid solubilization.



Blood lipids from the endothelial system



Fatty acids(FA)

Fatty acids fill two major roles in the body:

1. the components of more complex membrane lipids.

2. the major components of stored fat in the form of triacylglycerols.



C

haracteristics of fatty acids:� Fatty acids: long-chain hydrocarbon

molecules containing a carboxylic acid

moiety at one end.

� At physiological pH, the carboxyl group:

� readily ionized,� rendering a negative charge onto fatty acids

in body fluids



Lipids from bone tissue



C

haracteristics of fatty acids:

5 The numbering of carbons in fatty acids:5 begins with the carbon of the carboxylate group.

5 Fatty acids that contain no carbon-carbon double bonds:

5 saturated fatty acids.

5 those that contain double bonds:5 unsaturated fatty acids.



C

haracteristics of fatty acids:� The numeric designations used for fatty acids

come from the number of carbon atoms,

� followed by the number of sites of unsaturatione.g. palmitic acid :

� a 16-carbon fatty acid with no unsaturation siteand is designated by 16:0.



C

haracteristics of fatty acids� The site of unsaturation in a fatty acid is

indicated by the symbol D or :

� the number of first carbon of the doublebond (e.g. palmitoleic acid is a 16-carbon

fatty acid with one site of unsaturation

between carbons 9 and 10,)

� and is designated by 16:1 D9 or 16:1





C

haracteristics of fatty acids� Saturated fatty acids of less than eight

carbon atoms:

� are liquid at physiological temperature,� whereas those containing more than ten:

solid.

� The presence of double bonds in fatty acids:� significantly lowers the melting point

relative to a saturated fatty acid.



C

haracteristics of FA� The majority of body fatty acids: acquired

in the diet.

� However, the lipid biosynthetic capacity of the body (fatty acid synthase and other fattyacid modifying enzymes):

� can supply the body with all the variousfatty acid structures needed.



C

haracteristics of fatty acids� Two key exceptions for this supply:

� the highly unsaturated fatty acids;

� known as µlinoleic acid¶ and µlinolenicacid¶,

� containing unsaturation sites beyondcarbons 9 and 10.



C

haracteristics of fatty acids� These two fatty acids cannot be synthesized

from precursors in the body,

� and are thus considered the essential fattyacids;

� as they must be provided in the diet.



C

haracteristics of fatty acids� Since plants are capable of synthesizing

linoleic and linolenic acid:

� humans can acquire these fats byconsuming a variety of plants;

� or else by eating the meat of animals that

have consumed these plant fats.



Basic structure of triacylglycerides

� composed of a glycerol backbone(shown in blue) :

� to which 3 fatty acids are esterified.



Basic structure of p

hosp

holipids

� The basic structure of phospholipids is verysimilar to that of the triacylglycerides,

� except that C-3 ( sn3) of the glycerol backbone: esterified to phosphoric acid.

� The building block of the phospholipids:

phosphatidic acid.




h

osph

olipids

� Substitutions include:

� ethanolamine (phosphatidylethanolamine)

� choline (phosphatidylcholine, also calledlecithins)

� serine (phosphatidylserine)

� glycerol (phosphatidylglycerol)




h

osph

olipids

� Substitutions include:

� myo-inositol (phosphatidylinositol, these

compounds can have a variety in the numbers of inositol alcohols that are phosphorylatedgenerating polyphosphatidylinositols),

� and phosphatidylglycerol (diphosphatidylglycerolmore commonly known as cardiolipins).



Basic composition of a phospholipid. X can be a

number of different substituents



Basic structure of plasmalogens

� complex membrane lipids that resemble phospholipids,

� principally phosphatidylcholine.� The major difference:

� that the fatty acid at C-1 ( sn1) of glycerol containseither an O-alkyl (-O-CH2-)

� or O

-alkenyl ether (-O-C

H=C

H-) species.



Basic composition of O-alkenyl

plasmalogens



E

xamples� One of the most potent alkyl ether plasmalogens:

� platelet activating factor (PAF: 1-O-1'-enyl-2-acetyl- sn

-glycero-3-phosphocholine):� which is a choline plasmalogen:

� in which the C-2 ( sn2) position of glycerol:

� esterified with an acetyl group instead of a long

chain fatty acid.



E

xamples� PAF functions as:

� a mediator of hypersensitivity,

� acute inflammatory reactions and anaphylacticshock.



Platelet activating factor � PAF is synthesized in response to the formation of

antigen-IgE complexes;

� on the surfaces of basophils,� neutrophils,

� eosinophils,

� macrophages

� and monocytes.



E

xamples� The synthesis and release of PAF from cells:

� leads to platelet aggregation

� and the release of serotonin from platelets.� PAF also produces responses in:

� liver,

� heart,

� smooth muscle,� uterine and lung tissues.



Structure of plasminogen activation

factor



B

asic structure of sph

ingolipids� composed of a backbone of sphingosine

� which is derived itself from glycerol.

� Sphingosine is N-acetylated by a variety of fatty acids

generating a family of molecules referred to asceramides.

� Sphingolipids predominate in the myelin sheath of nervefibers.



B

asic structure of sph

ingolipids� an abundant sphingolipid

� generated by transfer of the phosphocholine moiety of phosphatidylcholine to a ceramide,

� thus sphingomyelin : a unique form of a phospholipid.� The other major class of sphingolipids (besides the

sphingomyelins):

� the glycosphingolipids:

� generated by substitution of carbohydrates to the sn1carbon of the glycerol backbone of a ceramide.



Sphingomyelin



E

xamples� There are 4 major classes of glycosphingolipids:

� Cerebrosides: contain a single moiety,

principally galactose.� Sulfatides: sulfuric acid esters of

galactocerebrosides.

� Globosides: contain 2 or more sugars.

� Gangliosides: similar to globosides except alsocontain sialic acid.



� Top: Sphingosine

the atoms in red are derived from glycerol.

Bottom: Basic composition of a ceramideµn¶ indicates any fatty acid may be N-acetylated at this position.



W

axes� Biological waxes:

� esters of long chain saturated andunsaturated fatty acids (having 14 to 36carbon atoms) with long chain alcohols(having 16 to 30 carbon atoms)



Beeswax



Properties of waxes� Their melting points:

� 60-100r C, higher than those of

triacylglycerols� e.g. in planktons:

� Waxes: the chief storage form of metabolic

fuel.� e.g. certain skin glands of vertebratessecrete waxes to protect the hair and skin.



Sterols� Structural lipids present in the membranes

of most eukaryotic cells.

� In animal tissues, cholesterol (cholest-5-en-3ß-ol):

� by far the most abundant member of a

family of polycyclic compounds known assterols.



Cholesterol

� It can also be described as a polyisoprenoid.

� Chevreul (French chemist):

� isolate it from gallstones,

� and characterize it as a single compound aslong ago as 1815.



Sterols� Cholesterol:

� has an important role in membranes and inlipid metabolism in general.

� Interestingly, the steroidal hormones,derived biosynthetically from cholesterol,

are not considered as lipids!!







C

holesterol� It occurs in the free form� and esterified to long-chain fatty acids (cholesterol

esters) in animal tissues, including the plasmalipoproteins.� Animals in general:� synthesize a high proportion of their cholesterol

requirement,� but they can also ingest and,

� absorb appreciable amounts in their diets.



C

holesterol� Many invertebrates,

� including insects, cannot synthesizecholesterol

� and must receive it from the diet;

� they can also make much more use of plant

sterols than do higher animals.



LITE

RATUR E

C

ITE

D� Devlin,T.M. Textbook of Biochemistry withClinical Correlations,Fifth Edition,Wiley-LissPublications,New York, USA, 2002.

� Lehninger, A. Principles of Biochemistry, Secondedition,Worth Publishers Co., New York, USA,1993.

� Matthews,C

.K. and van Holde, K.E

.,Biochemistry, Second edition, Benjamin /Cummings Publishing Company Inc., SanFrancisco, 1996.

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