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  1. 1. Chapter 12 LIPIDSnysha Page 1
  2. 2. What are lipids?Lipids are a family of substances that are insoluble inwater but soluble in nonpolar solvents of low polarity. Functions: - to store energy within fat cells - as part of membranes to separate compartments of aqueous solutions - to serve as chemical messengers Page 2
  3. 3. Classification of Lipids by Structure Page 3
  4. 4. Structure of TriglyceridesAnimal fats and vegetable oils aretriglycerides. Triglycerides are tri-esters ofglycerol and long-chain carboxylic acids calledfatty acids.The alcohol triglycerides is always glycerol. Page 4
  5. 5. The acid component of fats may be any number of acidwhich have certain things in common:1. Fatty acids are practically all unbranched carboxylic acids2. They range in size from about 10 – 20 carbons.3. They contain even number of carbon atoms.4. They have no functional groups except that some do have double bonds.5. In most fatty acids that have double bonds, the cis isomers predominate. Page 5
  6. 6. Fatty acids can be divided into two groups: saturated and unsaturated. Page 6
  7. 7. Saturated Fat→ Have single bonds in the hydrocarbon chain.→ Solid at room temperature because their aliphatic chain allows molecules to be packed in a parallel alignment.→ Interactions between neighboring chain are weak.Unsaturated Fat→ Have at least one C=C in the chain→ Liquid at room temperature because the cis double bonds interrupt the packing of chains Page 7
  8. 8. Lipids: MembranesComplex lipids form the membranes around body cells and around small structures inside the cells. Cell membranes separates cells from the external environment and provide selective transport for nutrients and waste products into and out of the cells. Page 8
  9. 9. - Membranes are made up of lipid bilayers where 2 rows of complex lipid molecules are arranged tail to tail→ Hydrophilic: Projects to the inner and outer layer of the membrane→ Hydrophobic: Tail points toward each other Page 9
  10. 10. - The unsaturated fatty acids prevent the tight packing of the hydrophobic chains in he lipid bilayer, thereby providing a liquid-like character to the membrane. -The lipid part serves as barrier against any movement of ions or polar compounds into and out of the cells. Page 10
  11. 11. In the lipid bilayer, protein molecules areeither suspended on the surface(peripheral proteins) or partly or fullyembedded in the bilayer (integral proteins). Page 11
  12. 12. Glycerophospholipids- Also called “Phosphoglycerides” and is very similar to that of fats.- Two of three – OH groups are esterified by fatty acids. The third is esterified by a phosphate gruop, which is also esterified to another alcohol. Page 12
  13. 13. - If the other alcohol is choline, a quaternary ammonium compound, the glycerophospholipids are called phosphatidycholines (common name: Lecithin) Page 13
  14. 14. Another example of glycerophospholipid iscephalins. Instead od choline, they containother alcohol such as serine orethanolamine. Page 14
  15. 15. - One important group of glycerophospholipids is Phosphatidylinositols (PI). In PI, the alcohol inositol is linked to the rest of the molecule by phosphate ester linkage. - This compound serves as signaling molecules in chemical communication. Page 15
  16. 16. Note:Glycerophospholipids are amphipathic —glycerol and phosphate form the polar endof the molecule, while hydrocarbon chainsform the nonpolar end. They are insoluble in water, but theirunique geometry causes them to aggregateinto bilayers without any energy input. Page 16
  17. 17. SteroidsSteroid is the 3rd major class of lipid and contains this ring system: They are not necessarily esters (although some are). Page 17
  18. 18. Cholesterol:- The most abundant and imortant steroid in the body.- Serves as a plasma membrane component in all animal cells.- Serves as raw material for the synthesis of other steroid.- Exist both in the free form and esterified with fatty acids. Page 18
  19. 19. - The cholesterol in our body is in a dynamic state which constantly circulates in the blood.- Being hydrophobic, it needs a water-soluble carrier to circulate in the aqueous medium of the blood. Page 19
  20. 20. LIPOPROTEINS – Carrier of Cholesterol - Cholesterol, along with fat, is transported bylipoproteins. Most of them contain a core ofhydrophobic lipid molecules surrounded by ashell of hydrophilic molecules. Four kinds of lipoproteins 1. High-density lipoprotein 2. Low-density lipoprotein 3. Very-low-density lipoprotein 4. Chylomicrons Page 20
  21. 21. Transport of Cholesterol in LDLStep 1: Transport of cholesterol begins when the liver secretes a VDL particle.Step 2 : When a VLDL particle reaches the capillary of muscle or adipose tissue, its triglyceride is extracted leaving a Intermediate Density Lipoprotien (IDL). Page 21
  22. 22. Step 3: Half of the IDL particles are removed from circulation by the liver within two to six hours of their formation.Step 4: The remaining IDL transform into LDL which circulate fo approximately two and a half days before binding to LDL receptors in the liver and other tissues. ** The LDL carries cholesterol to the cells, where specific LDL- receptor molecules line the cell surface in certain concentrated areas called coated pits. Page 22
  23. 23. Transport of Cholesterol in LDLStep 1: HDL transports cholesterol from peripheral tissues to the liver and transfers cholesterol to LDL.Step 2: While in the serum, the free cholesterols in HDL are converted to cholesteryl esters. Step 3: The esterified cholesterols are delivered to the liver for synthesis of bile acids and steroid hormones. Page 23
  24. 24. Step 4: In a selective lipid uptake, the HDL binds to the liver cell surface and transfers its cholesteryl ester to the cell.Step 4: After, the HDL, depleted from its lipid content, re- enters the circulation Page 24
  25. 25. Levels of LDL and HDL LDL CholesterolLDL cholesterol can build up on the walls of your arteries and increase your chances of getting heart disease. That is why LDL cholesterol is referred to as "bad" cholesterol. The lower your LDL cholesterol number, the lower your risk. Page 25
  26. 26. HDL CholesterolWhen it comes to HDL cholesterol -- "good" cholesterol -- the higher the number, the lower your risk. This is because HDL cholesterol protects against heart disease by taking the "bad" cholesterol out of your blood and keeping it from building up in your arteries. The table below explains what the numbers mean. Page 26
  27. 27. Steroid HormonesA. Adrenocorticoid Hormones - Products of of the adrenal glands.Two gruops:→ Mineralocorticoids (regulate the concentration of ions) Aldosterone is one of the most important mineralcorticoids. Increase secretion of this enhances the reabsorption of sodium and chlorine ions in the kidney tubules. Page 27
  28. 28. → Glucocorticoids (control carbohydrate metabolism). Cortisol is the major glucocorticoid. Its function is to increase glucose and glycogen concentration in the body. Also, with its ketone derivative (cortisone), it have a remarkable inflammatory effects in the body. Page 28
  29. 29. Sex HormonesTestosterone Promotes the normal growth of the male genital organs. Synthesized in the testes from cholesterol. Leads to secondary male sexual characteristics as deep voice and facial and body hair. Page 29
  30. 30. Estradiol Female sex hormone synthesized from testosterone by aromatization of the A ring. Regulates the cyclic changes occuring in the uterus and ovaries. Together with progesterone, it promotes further preparation of the uterine lining to receive the fertilized ovum. Page 30
  31. 31. Progesterone Stimulates and regulates various functions. Plays a role in maintaining pregnancy. The hormone is produced in the ovaries, the placenta (when a woman gets pregnant) and the adrenal glands. Cause the endometrium to secrete special proteins during the second half of the menstrual cycle Page 31