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Dr. Arrel Toews (say Tavz, like waves) 420 ME Jones Building 843-8727 Get UP To Speed (GUTS) Session on Lipids A primer on lipid structure,

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Presentation on theme: "Dr. Arrel Toews (say Tavz, like waves) 420 ME Jones Building 843-8727 Get UP To Speed (GUTS) Session on Lipids A primer on lipid structure,"— Presentation transcript:

1 Dr. Arrel Toews (say Tavz, like waves) 420 ME Jones Building Get UP To Speed (GUTS) Session on Lipids A primer on lipid structure, nomenclature, and function See also the GUTS session on Lipids notes (.doc) - self-assessment exam - additional lipid information

2 Definition: biomolecules that are overall hydrophobic - very non-polar - insoluble in water/aqueous solutions (cellular environment) - soluble in organic (non-polar) solvents (CHCl 3 -MeOH) - operational rather than structural definition Lipids (water-fearing) - contrast this with definitions for: proteins nucleic acids carbohydrates

3 - energy source (dietary triglycerides) - energy stores (adipose tissue triglycerides) - triglycerides are completely hydrophobic highly reduced (energy-rich) compact, efficient energy storage - membranes – amphipathic lipids (both hydrophobic and hydrophilic portions) - phospholipids - sphingolipids - cholesterol Lipid Functions Fatty acids are basic building block of most lipids - signaling molecules 2 nd messenger systems; eicosanoids; steroid hormones - fat-soluble vitamins: A (vision), D (bones/teeth), E (anti-oxidant; live forever), K (blood clotting)

4 H H H H H H H H H H H H H H H H H O l l l l l l l l l l l l l l l l l ll HC C C C C C C C C C C C C C C C C C-O- l l l l l l l l l l l l l l l l l H H H H H H H H H H H H H H H H H Stearic acid CH 3 (CH 2 ) 16 COOH Systematic: octadecanoic acid Shorthand: 18:0 (18C, no double bonds) Structure and nomenclature of fatty acids *All fatty acids ionized at physiological pH; pKa <5 * O ll CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 C-O - * O ll C-O - * Long-chain carboxylic acids; building blocks of most lipids

5 Linoleic acid CH 3 (CH 2 ) 4 CH=CHCH 2 CH=CH(CH 2 ) 7 COOH Systematic: cis, cis 9,12-octadecadienoic acid Shorthand: 18:2 6 This is shorthand for a fatty acid with 18 carbons and 2 double bonds. The 6 indicates the double bond closest to the methyl end is 6 carbons from the end. Structure and nomenclature of fatty acids If more than one double bond, the configuration is always methylene-interrupted (-CH=CH-CH 2 -CH=CH-) with cis double bonds. Always 3C between C=C bonds So - the term 18:2 6 completely defines the formula and structure of linoleic acid

6 Structure and nomenclature of fatty acids -designation important in nomenclature -oxidation of fatty acids CH 3 (CH 2 ) 14 COOH CH 3 (CH 2 ) 5 CH=CH(CH 2 ) 7 COOH CH 3 CH 2 CH=CHCH 2 CH=CHCH 2 CH=CH(CH 2 ) 7 COOH CH 3 (CH 2 ) 4 CH=CHCH 2 CH=CHCH 2 CH=CHCH 2 CH=CH(CH 2 ) 3 COOH CH 3 (CH 2 )CH=CHCH 2 CH=CHCH 2 CH=CHCH 2 CH=CHCH 2 CH=CHCH 2 CH=CH(CH 2 ) 2 COOH Try this at home: write shorthand names for the FA below Write the chemical formulas for 18:1 9 and 20:5 3 O ll CH 3 (CH 2 ) n CH 2 CHC-O - 18 or whatever generic fatty acid systematic biochemists no matter how long

7 Fatty Acids: long-chain carboxylic acids kinks – less packing – more fluid GOOD for membranes trans-FA are BAD! – no kinks, pack tightly; LDL; HDL (partially hydrogenated vegetable oils, Crisco, margarine) O ll *really CO - usually attached to glycerol as PL or TG Virtually all natural C=C double bonds are cis

8 hydrophobicity (long chain length) and fluidity (liquid at body temperature) both vital required biophysical properties - cell membranes - storage depots of energy (adipose tissue) Physiological functions of lipids – a problem But melting point increases with chain length So FA long enough to be hydrophobic are solids! (mp is above body temp) How does Mother Nature handle this??

9 18C fatty acids Number of carbon atoms Melting temperature (°C) Linolenic acid (18:3) Saturated fatty acids Stearic acid (18:0) Oleic acid (18:1) Linoleic acid (18:2) Melting points of fatty acids 18:4 -57 C Body temperature

10 The fatty acid composition of membrane lipids and adipose tissue triglycerides - chain length - degree of unsaturation is carefully regulated to maintain the appropriate fluidity Physiological functions of lipids

11 – much of it as triglyceride (mostly in adipose tissue) – also lots in phospholipids (major components of membranes) Most of the fatty acid in the body is esterified O ll CH 2 O C O ll CH O C glycerol Fatty acid composition is regulated to maintain correct fluidity (both TG and PL) - critical to biological function fatty acid Triglyceride energy source storage form

12 Phospholipids – vital components of membranes - glycerol backbone (like TG) - 2 FA in ester linkages - phosphate + X (choline, ethanolamine, serine, inositol) - amphipathic (amphi = both) GLYCEROL F A T T Y A C I D P e.g., choline + THE defining components of biological membranes - make lipid bilayers (2 molecules thick) Remember kinks in cis-double bonds of unsatd FA polar head long hydrophobic tail

13 phosphate glycerol Phosphatidylcholine (PC) Choline (polar X) 2 long-chain fatty acids aka lecithin a prominent phospholipid major membrane component involved in cholesterol handling too FA heterogeneity means many molecular species of PC

14 membranes 2 nd messenger signaling systems

15 Sphingolipids Structures and properties are generally similar to phospholipids (amphipathic) Phospholipids Glycosphingolipids F A T T Y A C I D O (usually) Long-chain amino alcohol (sphingosine) sugar(s) polar head long hydrophobic tail (more on these in Complex CH 2 O GUTS session)

16 Amphipathic nature of PL and sphingolipids is vital to life; makes membranes Lots more on this in Dr. Jacobsons Membranes GUTS lecture Phospholipid or glycolipid Polar head Hydro- phobic tail Micelle water Lipid bilayer water Hydrophobic tails hide from water

17 Cholesterol - rigid ring structure polar - a little bit amphipathic - membrane component (affects fluidity) - lipid transport in blood (atherosclerosis, &c)

18 Vocabulary – do you know the meaning of the following terms? lipid hydrophobic vs hydrophilic amphipathic fatty acid saturated vs unsaturated FA cis vs trans C=C double bonds shorthand nomenclature for FA triglyceride (and mono- and diglyceride) phospholipid sphingolipid cholesterol


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