1. Chapter 20 Lipids

2. Lipids 3 major roles in biochemistry 3 major roles in biochemistry Store E within fat cells (vs plants – cellulose)Store E within fat cells (vs plants – cellulose) Membranes to separate compartments (e.g. lipid bilayer)Membranes to separate compartments (e.g. lipid bilayer) Chemical messengers (e.g. hormones)Chemical messengers (e.g. hormones) Classification: (4 groups/types) Classification: (4 groups/types) 1. simple lipids (fats, waxes) 2. complex lipids (phospho/glyco-lipids) 3. steroids (cholesterol) 4. prostaglandins, thromboxanes, leukotrienes (inflammation) (inflammation)

3. Structure of Triglyceride Triglyceride: Triglyceride: an ester of glycerol with three (1-3) fatty acids (F.A.s). 1. 2. 3. Confirming your knowledge: Draw the structural formula of a triglyceride of: myristic, palmitic and oleic acid and glycerol See table 20.1 p 496 + 3 F.A.s  + 3 H 2 O

4. Properties of Triglycerides 1. Physical properties depend on the fatty acid components: Melting points, Oils and Fats Longer Carbon chain(s)  higher M.P. More d. bonds (unsaturated) lower M.P. RECALL Oils = liquid at room temp. b/c lots of d.bonds (as cis form) Fats = solid at room temp. b/c few d. bonds (stack easily) NOTE: Natural form of d. bonds in fatty acids/ oils = always cis or trans? e.g. the Essential Fatty Acid (EFA) linoleic acid

5. CHALLENGE QUESTION Linoleic acid has M.P. of -5 *C. What would happen to it’s M.P. if you converted the cis d. bonds to trans and why?

6. 2. Hydrogenation reduction of some or all d. bonds of an unsaturated triglyceride w/ H 2 /transition metal catalyst. Why? Easier kitchen use (e.g. Crisco oil etc) Better for baking, mixing, longer shelf life, cheaper Formation of mainly trans isomers (Trans fats) e.g. partially hydrogenated vegetable oil Drawbacks: unnatural, body does not recognize “trans” form Inflammation, weight gain, heart disease (higher cholesterol) Properties of Triglycerides

8. 3. Saponification Hydrolysis of esters: using base Produces glycerol + mixture of fatty acids aka (SOAPS) Properties of Triglycerides Note: Hard water disrupts soaps Mg 2+ or Ca 2+ Binds to fatty acids see chem conn. p.500 Polar Head Greasy tail

9. Complex Lipids 1. Phospholipids contain an alcohol, two fatty acids, and a phosphate ester. a. in glycerophospholipids, the alcohol is glycerol. (plasma membranes) b. In sphingolipids, the alcohol is sphingosine. (function in coatings neurons) 2. Glycolipids Complex lipids that contain a carbohydrate.

10. polar Non polar ((Water))

11. glycerophospholipid Soap = “ Micelle” (traps dirt/grease )

12. 20.5 Membranes Complex lipids form the membranes around cells and small structures within cells. complex lipids spontaneously form into a lipid bilayer with a back-to-back arrangement of lipid monolayers. 1. Polar (hydrophilic) head groups are in contact with the aqueous environment. 2. Nonpolar (hydrophobic) tails are buried in bilayer shielded from environment. - driving force of lipid bilayers = hydrophobic interaction. The arrangement of hydrocarbon tails in the interior can be rigid (saturated fatty acids) or fluid (unsaturated fatty acids). ((water)) 2. 1.

13. Fluid Mosaic Model Lipid types most likely found in membranes: glycolipids, & cholesterol transport

14. 1a. Glycerophospholipids second most abundant group of naturally occurring lipids. Occur in plant and animal membranes: ( 40% -50% phosphoacylglycerols) (50% - 60% proteins) most abundant glycerophospholipids derived from phosphatidic acid The three most abundant fatty acids in phosphatidic acids are palmitic (16:0), stearic (18:0), and oleic (18:1).

15. 1a. Glycerophospholipids A phosphatidic acid 1. glycerol is esterified with: 2. two molecules of fatty acid 3. one phosphoric acid. 1. H H 2. 3. H

16. 1a. Glycerophospholipids cont. 3 other types: -Ethanolamine -Serine -Inositols

17. Glycerophospholipids Challenge Question (Homework) Which Glycerophospholipids will have the greatest solubility in Water: ethanolamine? choline? serine? glycerol ? ? ?

18. Sphingolipids Found in the coatings of nerve axons (myelin). Contain the long-chain aminoalcohol, sphingosine, from which this class of compounds in named.

19. Sphingolipids make up myelin See chem. Connections 20E p.506, Swine flu, watch out!

20. Glycolipids Glycolipid: Glycolipid: a complex lipid that contains a carbohydrate. The carbohydrate is either glucose or galactose. The cerebrosides are ceramide mono- or oligosaccharides.

21. Steroids Steroids: Steroids: a group of plant and animal lipids that have this tetracyclic ring structure. Know this backbone

22. A. Cholesterol Cholesterol is the most abundant steroid in the human body, and most important. Why? 1. It is a component in plasma membranes in all animal cells. 2. It is the precursor of all steroid hormones and bile acids. -CONFIRMING your Knowledge- How many stereocenters exist in cholesterol? Gallstone of cholesterol

23. B. Lipoproteins Cholesterol, along with fats, are transported by lipoproteins proteins Cholest Mostly fat

24. Lipoproteins Figure 20.5 Schematic of a low-density lipoprotein (LDL).

25. Cholesterol Transport Cholesterol made in Liver Transport of cholesterol from the liver starts out as VLDL. VLDL is carried in serum (blood) to fat or muscle tissues and... deposits proteins and triglycerides.. As fat is removed, (diameter shrinks) its density increases (i.e. VLDL  LDL) LDL stays in the plasma for about 2.5 days.

26. 1. LDL carries cholesterol to cells, where specific LDL receptors bind it. 2. After binding, LDL is taken into cells where enzymes liberate free cholesterol and cholesteryl esters. 3. LDL receptor then recycled to “Pit” Cholesterol Transport cont. 1. 2. 3.

27. What happens to patients who have limited LDL receptors on there cell membranes? (i.e. familial hypercholesterolemia) Challenge Question?

28. Cholesterol Transport 1. High-density lipoproteins (HDL) transport cholesterol: f/ tissues  liver and also transfer cholesterol to LDL. While in the serum, free cholesterol in HDL is converted to cholesteryl esters. 2. In the liver, HDL binds to the liver cell surface and transfers its cholesteryl esters to the cell. These esters are used for the synthesis of steroid hormones (estrogen, testosterone) and bile acids. After HDL has delivered its cholesteryl esters to liver cells, it reenters circulation. 1. 2.

29. Levels of LDL and HDL Most of the cholesterol is carried by LDL. If sufficient LDL receptors on the surface of cells, LDL is removed from circulation and its concentration in blood plasma drops. number of LDL receptors is controlled by a feedback mechanism. When [cholesterol] inside cells is high, the synthesis of LDL receptors is suppressed. (inside liver) Normal plasma levels: 175 mg/100 mL. “hypercholesterolemia” plasma levels: 680 mg/100 mL! Not enough LDL receptors

30. Levels of LDL and HDL These high levels of cholesterol can cause premature atherosclerosis (myocardial infarction: MI) and heart attacks. High LDL means high cholesterol content in the plasma because LDL cannot get into cells. Therefore, high LDL together with low HDL is a symptom of faulty cholesterol transport and a warning of possible atherosclerosis. Get tested?!?.. Simple blood test, Planned parenthood, Longs etc.

31. Reg. Exercise, Diets low in cholesterol and sat. fat reduce serum cholesterol The commonly used statin drugs (Lipitor) inhibit the synthesis of cholesterol by blocking HMG-CoA reductase in the liver Treating High Cholesterol

32. Steroid Hormones Androgens: Androgens: male sex hormones synthesized in the testes responsible for the development of male secondary sex characteristics