Lipids and membranes

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Biochemistry
Second Year

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Lipids and membranes

  1. 1. LIPIDS AND MEMBRANES Membranes are: sheet like, few molecules thick, closed boundaries, asymmetric. Lipids Proteins Carbohydrates Lipids : bilayer, barrier for polar molecules. Proteins : function as pumps, gates,receptors,enzymes, etc. Carbohydrates: signal, receptor (cell-cell recognition), etc. LIPIDS Water insoluble, highly soluble in organic solvents.Role : -Fuel molecules & energy stores -Membranes -Protection -Precursors for hormones, prostaglandins, etc. CLASSES 1.Triacylglycerol.(Triglycerides, TG)(neutral fat). Fats and oils are TG . TG is a glycerol with 3 -OH groups esterified with fatty acids. H FA OCH2 H FA OCH H FA O CH2 Fatty acids (FA): is a long HC chain carboxylic acid. 12 – 24 C (common 16 – 18 C ). Saturated and Unsaturated. Nomenclature of FA : from #C , or common name. Sat.unsat. 18C octadec an oic acid 9-octa dec en oic acid (stearic acid) -9 (oleic acid) 9,12-octa dec di en oic acid ( linoleic acid )
  2. 2. TG sat. FAfat ( m.p.) more vanderwaal unsat. FA oil (m.p.) less vanderwaal TG is the storage form of lipid in adipocytes (adipose tissues). 2.Glycerophospholipid. (Phophoglycerides) Glycerol backbone in which two –OH groups are esterified to FAs, and one –OH is esterified to phosphoric acid to give the smallest (parent) phosphoglyceride called phosphotidic acid. Phosphate could be esterified (i.e. –H is substituted) by one of several alcohols :- e.g. ethanolamine ………… phosphotidyl ethanolamine Choline ………….. phosphotidyl choline 3. Sphingolipid Instead of glycerol the backbone is " ceramide" , which is sphingosine long unsat. HC chain amine alcohol in which amine is condensed with FA.
  3. 3. 1° -OH group is esterified to give Three different subclasses : ( l ) Shingomyelin Found in myelin surrounding nerves isolating them. ( ll ) Cerebroside Found in neuronal cell membrane of brain. (lll )Gangliosid brain lipid (constitutes receptor for pituitary gland hormone). 4. Cholesterol Found in plasma membrane of eukaryotic cells. Lipoproteins TG ,cholesterol and other lipids are transported as lipoprotein (non-covalent binding). Lipoprotein particle consists of : a core of hydrophobic lipids surrounded by a shell of polar lipids(e.g. phospholipid). Essential and Non-essential fatty acids Essential FAs are important for body function but not synthesized in our body. They have double bonds at less than C9 from methyl end (ω9). PROPERTIES OF LIPID AGGREGATION Phospholipids, sphingolipids, and cholesterol are amphiphilic molecules: hydrophilic part(charged or polar) + hydrophobic part ( HC ) can form closed bilayer sphere or lipid vesicle "liposome" as in cell membrane, impermeable to ions & most polar molecules.
  4. 4. Lipoproteins TG ,cholesterol and other lipids are transported as lipoprotein (non-covalent binding). Lipoprotein particle consists of : a core of hydrophobic lipids surrounded by a shell of polar lipids(e.g. phospholipid) and apoprotein. Essential and Non- essential fatty acids Essential FAs are important for body function but not synthesized in our body. They have double bonds at less than C9 from methyl end (ω9).

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