Lipids Lecture 1 PDF

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Summary

LipidsFatty Acids Present in more complex lipids  Long chain of hydrocarbon tail - non-polar - C16 & C18 most common (usual range C12 – C20)  Carboxyl group at 1 end - pKa = 4- - Usually bonded to another group in vivo.  Variables that change boiling points - Length - SaturationNaming Syste...

Description

Lipids Fatty Acids  

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Present in more complex lipids Long chain of hydrocarbon tail - non-polar - C16 & C18 most common (usual range C12 – C20) Carboxyl group at 1 end - pKa = 4.7-5 - Usually bonded to another group in vivo. Variables that change boiling points - Length - Saturation

Naming  

Systematic (C1 being the carboxylic acid) Alternative (using n to donate methyl carbon)

Saturated   

If the acid is ionised (pyruvic acid to pyruvate) Palmitate (ionised from palmitic acid Higher melting point as they have a greater surface area

Unsaturated        

Trans and cis interactions All fatty acids are in the cis form Trans are more energetically stable Cis are more biologically beneficial ω 6 carbon means that double bond on C6 Double bonds are always 3C apart Fish are a good source of ω3 Plants are a good source of ω6

Examples Steric Acid    

Most common saturated acids Octadecanoic acid (18:0) = 18 Carbon atoms, 0 double bonds Common in animal products Used in the production of detergents, soaps and cosmetics such as shampoos and shaving cream

Palmitic Acid   

Hexadeconoic acid (16:0) Biofuels Found in fats and waxes including olive oil, palm oil, and body lipids

Oleic Acid

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Most common monounsaturated fatty acid cis – Δ9 - Octadecanoic Acid (18:1(n-9) or 18:cis-9) Incorporated into cell membranes and important in membrane fluidity

Essential Fatty Acids 1. Alpha Linolenic Acids - Octadecatrianoic acid - 3 double bonds - cis cis cis Δ9Δ12Δ15 or cis cis cis-9,12,15 - (18:3) 2. Linoic Acid - Octadecadienoic acid - cis cis Δ9Δ12 - ω6 3. Arachidonic - Essential in deficient in Linoleic acid - Eicosteteraenoi acid 20:4(n-6) or 20:4 cis cis cis cis Δ5Δ8Δ11Δ14 (all cis-5, 8, 11, 14) - Essential because humans cant insert double bonds beyond (n-9) - Precursors for important molecules such as prostaglandins and the leukotrienes, both of which are also unsaturated carboxylic acids Triacylglycerol (TAG)   

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Non-polar Usually variable FAs on each glycerol Mostly saturated - Solids at room temp - Animal fats e.g. lard, butter Unsaturated - Liquid at room temp - Plant oils e.g. vegetable oil

ω6 =15:1 ω3 ω6 = 2:1 - 4-1 ω3

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Modern diets

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Suggested

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Reduced mortality from cardiovascular disease Reduced inflation e.g. Rheumatoid arthritis Reduced risk of breast cancer

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Naming of TAGS 

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Simple TAGS - 3 identical fatty acid chains - 3 acid chains in trisearoylglycerol - 3 acid residues trioleolglycerol (triolein) Mixed TAGS Named according to position on glycerol 1-palmitoleoyl-2-linoyl-3-stearoyl-glycerol

Functions of TAGs        -

Insulation Protection Store energy Complete oxidations of fatty acids = 38KJ/g energy to convert dietary fat into stored = 3% Carbohydrates = 17KJ/g energy to convert dietary carbohydrate into stored ~25% 3g water associated per 1g Denser as an energy source as it is hydrophobic 9 fold difference in energy 250g=2kg of potatoes Body weight if all energy stored as carbohydrate would be 120-160kg (not 65-70kg)

Phospholipids   

Phosphate occupies the 3rd position point on glycerol Glycerophospholipids (Phosphoglycerides) Phosphoglyceride = Amphiphilic (an ampholyte)

Most Common Head Groups

Sphingolipids

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Hydrocarbon tail with polar group Membrane lipis Sphingosine instead of glycerol 2 other positions 1. Fatty Acid - via amino group, forms a Ceramide 2. Phosphate - Frequently an amino alcohol is then attached to the Phosphate e.g. Choline, Ethanolamine

Sphingomyelin        

25% of all lipids in humans Phosphorylcholine Usually 2 straight chains Gives tighter packing Stable membrane Alters fluidity Used to insulate axons Forms myelin sheath

Glycolipids     

Contain a carbohydrate e.g. galactose or glucose Molecule is amphipathic Specialised membrane component Common in plant cells and cells of nervous system Act as recognition molecules e.g. blood groups

Steroids    

Only found in eukaryotes (Hopanoids in prokaryotes) 4 fused rings Relatively non polar Cholesterol

Cholesterol         

Membrane fluidity Increases rigidity it high temperatures by restricting the degrees of freedom (restricting entropy/disorder) Restricts movement of neighbouring fatty acids Precursor for sex hormones, glucorticoids, mineral corticoids, vitamin D and bile salts Most common steroid Amphipathic Major component animal plasma membranes Lesser amounts in organelle membranes Structure rigid & flat

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Simvastatin Unable to crystallise as fatty acids are kept apart at low temperatures

Terpenoids  

Synthesised from isoprenoids Precursor for a range of molecules - Vitamin A - Vitamin K - Both vitamins are fat soluble

Lipoproteins  

Lipid + protein Transport of fatty acids in circulation

Lipopolysaccharides 

Lipids + carbohydrate

Waxes   

Flat structure Can pack/associate closely together Long alcohol + long fatty acids bonded by an ester...