membrane lipids & its types

lipids are categorized into 4 major categories.
1) phospholipids
2) glycolipids
3) steroids
4) archeal membrane lipids

1. Membrane lipids and types (lecture # 2)

2. . Learning objectives O rganization of membrane system Properties of membrane lipids Classification of membrane lipids Structure of membrane lipids Structure and properties of :- : Glycolipids : Phospholipids : Sterols : Archaebacterial Ether Lipids

3. Biological Membrane Biological membrane system.• Membranes are two layers thick sheath like structures Formed by non-covalent assemblage of lipids and proteins Mainly consists of Lipids, Proteins and Carbohydrates Thickness of membrane: 60 A (6 nm) to 100 A (10 nm) Membrane forms closed boundaries between different compartments Act as barriers to the passage of polar molecules and ions Bio-membranes are Asymmetric: Components of two faces always differ from each other.

4. Membrane lipids Membrane lipids have hydrophilic (polar) & hydrophobic (non-polar) parts One end is hydrophilic and the other end is hydrophobic Their hydro p hobic interactions with each other and their hydro p hilic interaction with water direct the packing of lipids in the membrane Polar Region Lipid Bilayer of Plasma teo‹bzaoe LipidLayer2

5. Membrane lipids classification Membrane lipids are classified based on the properties of ‘head’ group Membran e lipid s of Prokaryotes , Eukaryotes an d Archaebacteri a are grouped into Four major categories: Phospholipids ( Glycero -phospholipids, Sphingo -phospholipids ) Glycolipids ( Galactolipids, sphingo -glycolipids ) Sterols Archoeb a cteriol ether lipids

6. MEMBRANE LIPIDS (1 ). Phos pholipids Glycerol-3-phosphate is the backbone of all phospholipids Here a polar head group is joined to the hydrophobic moiety by a phosphodiester linkage Other two —OH groups (C1 and C2) are esterified by fatty acids (R & R )

7. Phospholipids ( A ). Glycerophospholipids • Also called as phos cerides Major lipid component of biological membrane Consists of glycerol-3-phosphate, whose C 1 & C 2 esterified by fatty acids The C3 is linked to a polar group - ’X’ In simplest glycero-phospholipid, the ’-X’ is - H, is called p h osphatidic acid

8. Name of X-OH Formula of X Phospholipid name Water —H Phosphatidic acid Ethanolamine —C H 2 CH 2N H 3 + Phosphatidylethanolamine Choline — CH2CH2 N(CH 3 ) 3 Phosphatidylcholine [Lecit hin ) Serine —C H 2 C H(NH 3+ )C00 Ph osphatidylserine Glycerol — CH2C H(0H)CH 2 0H Phosphatidylglycerol Pho s pha tidylglycerol —CH2C H(0H)CH20H d iphosphatidylglycerol ( car diolipin) Phopho lipids Phospho-glycerolipids are of differen t fypes based on ’X’proup (table ) i›

9. Phospholipids (1 ). Glycerophospholipids .• Cardiolipin: an important component of the inner mitochondrial membrane It constitutes 20% of the total lipids of inner mitochondrial membrane The only other place where cardiolipin can be found is in the membranes of most bacteria Thus it is an evidence for endosymbiont theory

10. Phospholipids (1 ). Glycero phos pholipids.• Plasmalogen: They are glycero-phospholipids in which the C 1 of glycerol moiety is linked via an α ,𝛽 -unsaturated ether linkage rather than an ester linkage Ethanolamine, choline & serine are the most common plasmalogen heads Function of plasmalogens are not well understood OH Plasmalogen Backbone

11. Phospholipids (B ). Sphin g o -phospholipids: 8 Major class of membrane lipids 8 Named after Sphinx because of their function in the cells was mysterious 8 Most of the spingolipids are derivatives of C18 amino alcohol Sphingosine 8 N-acyl fatty acid derivative of sphingosine are known as ceraminde Sphingo -phospholipid H O H OH i i i C C H I I H N’ CH II H O H OH I I I H 2 C — C C H I I H C M H W C CH i ii I I 16 Sphingosine

12. Phospholipids ( B). Sphingophspholipids : Sphingomyelins & Most common sphingolipid ¥ Make up 10 — 20 % of plasma membrane lipids 4 They are ceramides with phosphocoline or phosphoehtanolamine head Myelin sheath of nerve cell axons are rich in sphingomyelins Electron m icrog r aph of m yelinated ner ves.- See the spir ally wrapped membrane around each nerve axon. Myelin sheath may be 10 -15 layers thick and the hig h lipid content makes it an electrical insulator

13. Membrane lipids CH OH HO H OH C H — 0— C ' I II (2 ). G lycolipids .• O Lipids conjugated with carbohydrates R Three main role: O Part of biological membrane system R Provide energy O Markers for cellular recognition II Giycolipid

14. Glycolipids Glycolipids.• Different class of glycolipids are: H (A). G l yceroglycolipids : Glycerole backbone with carbohydrates Galactolipids Sulfolipids H (B). Sphingo-glycolipids: Sphingosine backbone with carbohydrates Cerebrosides Globosides Gangliosides

15. Glycolipids CH 2 OH o O -CH 2 O ( 2 ). Glycolipids: (A). Glycero-glycolipids: —+ Galactolipids M One or two galactose residues present M Galactose connected by a glycosidic linkage to C3 of a Glycerol M C 1 and C 2 of glycerol are esterified with fatty acids Galactolipid Monogalacto s yldiacylglycerol(MGDG )

16. Glycolipids (2). Glycolipids: (A). Glycero-glycolipids: —+ Galactolipids Galactolipids are predominant in plant cells They are abundant in thyla k oid membrane of chloroplasts They constitut e 70%-80% of membrane lipids of vascular plants Probably they are the most abundant membrane lipids in the biosphere

17. Glycolipids I Galactolipids of chloro p lasts•“ GM H H OH H FI City H N .CH — O C n D i alactoeyldiacylglycerol (ñ4GDG] O — CHP HO OI3 H DH Monogalactosyldiacylglycerol (MGDG)

18. Glycolipids (2 ). Glycolipids .• (A ). Glycero-glycolipids.• —+ S ulfolipids .• A class of glycero-glycolipid with sulfur containing functional groups » Sulfonated glucose is joined to the C3 of diacylglycerol in glycosidic linkage Plant membranes also contain sulpholipids » Sulfonate head hold negative charge (like phosphate group in phospholipids) O = S - CH, CH 2 — C F'atty Acid Residues CH— 0— C —CH O Sulfolipid

19. Glycolipids (2 ). Glycolipids: (B). Sphingo-glycolipids: G A category of glycolipid fl Contains an amino alcohol sphingosine instead of glycerol G N-acyl fatty acid derivative of sphingosine are known as ceramide H O H OH i i i H 2 C fl Sphingo-glycolipids includes: Cerebrosides Gangliosides Globosides C C H I I H3 N ’ C H II CH H O H OH C H I I I H 2 C — I I H C I'm H O C C H I I Sphingosine

20. Glycolipids (2 ). Glycoli p ids.• (B ). Sp hingo -glycoli p ids.• a ). Cerebrosides.• It is a ceramide with single sugar residue at the Cl-hydroxyl moiety Sugar residue can be either glucose or galactose Thus two categories: Glucocerebrosides, Galactocerebrosides Cerebrosides lack phosphate groups and thus they are nonionic (no charge) Abundant in animal muscle and nerve cell membranes Galactocerebrosides are typically found in nerves Glucocerebrosides are found in other tissues , I! CH .OH ‹›j4 H H oH ft I I

21. Glycolipids (2 ). Glycolipids .• (B). Sphingo glycolipids .• b ). Globosides.• A sphingo-glycolipidwith more than one sugars as side chain of ceramide Sugars are usually a combination of N-Acetylgalactosamine, D-glucose or D- galactose Globoside

22. Glycolipids (2 ). Glycolipids .• (B). Sphingo glycolipids .• c). Gangleosides.• A glyco-sphingolipid (ceramide & oligosaccharide) with one or more sialic acids linked on the sugar chain —— Most complex sphingo-glycolipid 6% of brain lipids are gangleosides First isolated from ganglion of brain cells Abundant in lipid-rafts of plasma membrane

23. MEMBRANE LIPIDS (2 ). G lycolipids • (B ). Sphingoglycolipids .• c). Gangleosides.• Physiological/Medical significance of Gangleosides: Considerable physiological and medical significance Act as specific receptors for glycoprotein hormones Act as receptors for some bacterial protein toxins such as cholera toxin Act as specific determinants of cell—cell recognition (important in growth and differentiation of tissues and in carcinogenesis) Tay-Sachs disease is a hereditary disorder of ganglioside breakdown leading to fatal neurological deterioration in the early childhood

24. MEMBRANE LIPIDS M Sterol consists of four fused carbon rings (A, B, C, D) and an alkyl side chain M Alkyl chain is called 'hydrocarbon side chain’ M Ring A, B and C are with six carbons and Ring D is with five carbons M This fused ring is called the Steroid Nucleus M Steroid nucleus is derived from cyclopentanoperhydrophenanthrene M Fused ring structure do not allow C — C free rotation M Third major class of membrane lipids M Usually present in the membranes of eukaryotic cells opentanoperJdrephennnthreae

25. MEMBRANE LIPIDS M Cholesterol is a major sterol of animal membranes M Constitute about 30-40% all membrane lipids in animals M Cholesterol is amphipathic with polar hydroxyl (-OH) ’head’ and non- polar hydrocarbon ’tail’ M The —OH an d th e hydrocarbo n chai n ar e attache d t o th e C3 an d CI 7 of steroid nucleus respectively

26. MEMBRANE LIPIDS (3). S terols.• fl Cholesterol can esterify with long chain fatty acids to form cholesteryl esters such as cholesteryl stearate

27. MEMBRANE LIPIDS (3). S terols.• In mammals, cholesterol is the metabolic precursor of steroid hormones Cholesterol very rarely found in plants (other sterols occurs in plants) Stigmasterol: important membrane sterol in plants (phytosterol) Canipesterol and sitosterol are other plant sterols Ergosterol: sterol found in fungal membrane system OH C£t

28. MEMBRANE LIP IDS Bacteria cannot synthesize any sterol Thus bacterial membrane generally lacks sterol Some bacteria can incorporate exogenous sterol in to their membrane Lanosterol: sterol precursor of animals and fungi Cycloartenol: sterol precursor of plants Both Lanosterol and Cycloartenol are derived from the cyclization of triterpenoid squalene

29. MEMBRANE LIPIDS (4 ). Archaebacterial ether lipids.• Fourth major class of membrane lipids They are membrane lipids of archaebacteria Absent in prokaryotes and eukaryotes Majority of archaebacteria lives in extreme conditions (high temperature) Archaebacterial ethe r lipid s contai n lon g (3 2 C ) branche d hydrocarbon chains linked at both end to glycerol Linkages are through ether bonds (R — O — R’)

30. MEMBRANE LIPIDS 3. Archaebacterial et her li p ids.• Ether bonds are more stable than ester bonds They are twice the length of phospholipids and sphingolipids They span the width of the surface membrane At each end of the molecule two glycerol moieties are present This glycerol is linked to either phosphate or sugar residues