Lipids: structure, functions and health.
- 1. NUTRITION & HEALTH CHAPTER 4: LIPIDS AND HEALTH
- 2. LEARNING OUTCOMES • By the end of this lecture, student should be able to: Understand what is lipid Explain the importance of lipid Describe the structures of lipid Describe properties and function of lipid Differentiate types of lipid Explain the differences between saturated, unsaturated and trans fat Explain the metabolism of lipids Explain on the health risks of lipids
- 4. WHAT IS LIPIDS? Lipids are the one class of large biological molecules that does not include true polymers, and they are generally not big enough to be considered macromolecules. The compounds called lipids are grouped together because they share one important trait: They generally mix poorly with water. The hydrophobic behavior of lipids is based on their molecular structure. Although they may have some polar bonds associated with oxygen, lipids consist mostly of hydrocarbon regions. The biologically important types of lipids: fats, phospholipids, and steroids.
- 5. FATS Although fats are not polymers, they are large molecules assembled from smaller molecules by dehydration reactions. A fat is constructed from two kinds of smaller molecules: glycerol and fatty acids. Glycerol is an alcohol; each of its three carbons bears a hydroxyl group. A fatty acid has a long carbon skeleton, usually 16 or 18 carbon atoms in length. The carbon at one end of the skeleton is part of a carboxyl group, the functional group that gives these molecules the name fatty acid. The rest of the skeleton consists of a hydrocarbon chain. 5
- 6. FATS • The relatively nonpolar C–H bonds in the hydrocarbon chains of fatty acids are the reason fats are hydrophobic. • Fats separate from water because the water molecules form hydrogen bond to one another and exclude the fats. 6
- 7. FATS In making a fat, three fatty acid molecules are each joined to glycerol by an ester linkage, a bond between a hydroxyl group and a carboxyl group. The resulting fat, also called a triacylglycerol/triglyceride. The major function of fats is energy storage: A gram of fat stores more than twice as much energy as a gram of a polysaccharide, such as starch. Humans and other mammals stock their long-term food reserves in adipose cells. 7
- 8. Abdominal obesity in men ("beer belly") 8
- 9. SATURATED AND UNSATURATED FATS The terms saturated fats and unsaturated fats are commonly used in the context of nutrition, which refer to the structure of the hydrocarbon chains of the fatty acids. Saturated fatty acid: no double bonds between carbon atoms. Unsaturated fatty acid: has one or more carbon-carbon double bonds. Nearly all double bonds in naturally occurring fatty acids are cis double bonds, which cause a kink in the hydrocarbon chain wherever they occur. 9
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- 12. SATURATED FATS A fat made from saturated fatty acids is called a saturated fat. Most animal fats are saturated: The hydrocarbon chains of their fatty acids—the “tails” of the fat molecules—lack double bonds, and their flexibility allows the fat molecules to pack together tightly. Saturated animal fats—such as lard and butter—are solid at room temperature.
- 13. UNSATURATED FATS In contrast, the fats of plants and fishes are generally unsaturated, meaning that they are built of one or more types of unsaturated fatty acids. Usually liquid at room temperature, plant and fish fats are referred to as oils—olive oil and cod liver oil are examples. The kinks where the cis double bonds are located prevent the molecules from packing together closely enough to solidify at room temperature.
- 14. PHOSPHOLIPIDS Phospholipids are essential for cells because they make up cell membranes. A phospholipid is similar to a fat molecule but has only two fatty acids attached to glycerol rather than three. The third hydroxyl group of glycerol is joined to a phosphate group, which has a negative electrical charge in the cell. Additional small molecules, which are usually charged or polar, can be linked to the phosphate group to form a variety of phospholipids. 14
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- 16. PHOSPHOLIPIDS The two ends of phospholipids show different behavior toward water. The hydrocarbon tails are hydrophobic and are excluded from water. The phosphate group and its attachments form a hydrophilic head that has an affinity for water. When phospholipids are added to water (at the surface of a cell), they self- assemble into double-layered structures called bilayers. The hydrophilic heads of the molecules are on the outside of the bilayer, in contact with the aqueous solutions inside and outside of the cell. The hydrophobic tails point toward the interior of the bilayer, away from the water. 16
- 17. PHOSPHOLIPIDS The phospholipid bilayer forms a boundary between the cell and its external environment.
- 18. STEROIDS Steroids are lipids characterized by a carbon skeleton consisting of four fused rings. Different steroids, such as cholesterol and the vertebrate sex hormones, are distinguished by the particular chemical groups attached to this ensemble of rings. 18
- 19. What is cholesterol? Stabilizes cell membranes for proper function. Precursor to essential steroid hormones like estrogen, testosterone, cortisol, and vitamin D. Converts into bile acids for dietary fat digestion and absorption. Produced by liver and dietary sources like meat, eggs, and dairy. Hydrophobic molecule, cannot travel freely through water-based bloodstream. Transported by lipoproteins.
- 20. How cholesterols are transported in the body? Lipoproteins are particles made of lipids and proteins, responsible for transporting cholesterol and other lipids through the bloodstream. The major classes of lipoprotein particles are Chylomicrons Very-low density lipoproteins (VLDL) Low-density lipoproteins (LDL) High-density lipoproteins (HDL)
- 24. 24 A high level of cholesterol in the blood may contribute to atherosclerosis.
- 26. ENERGY STORAGE • Triglycerides, composed of three fatty acids and a glycerol backbone, are the body's primary energy storage. • Stored primarily in adipose tissue, they are highly efficient. • Lipids provide more energy per gram than carbohydrates or proteins (about 9 kcal/g for lipids vs. 4 kcal/g for carbs/proteins). • During energy deficits, triglycerides are broken down into fatty acids and glycerol. • Fatty acids are oxidized for energy in tissues, while glycerol is used to produce glucose in the liver.
- 27. STRUCTURAL ROLE • Phospholipids form a unique lipid bilayer, regulating substance entry and exit. • The bilayer's flexibility and fluidity enable cell shape changes and essential functions like signaling and nutrient transport. • Other lipids like cholesterol contribute to membrane stability and fluidity at different temperatures.
- 28. HORMONE PRODUCTION • Lipids, particularly cholesterol, serve as the precursors to steroid hormones. • Steroid hormones include important hormones like cortisol, estrogen, testosterone, and progesterone, which regulate various physiological processes such as metabolism, stress response, and reproduction. • Cholesterol is modified in the adrenal glands and gonads (testes and ovaries) to produce these hormones. • These steroid hormones are lipid-soluble, which allows them to pass through cell membranes and interact with intracellular receptors to regulate gene expression.
- 29. INSULATION AND PROTECTION • Adipose tissue stores energy and acts as an insulating barrier, maintaining body temperature. • Subcutaneous fat acts as a barrier, preventing heat loss in cold conditions. • Adipose tissue retains body heat, keeping internal organs at optimal temperatures. • Fat acts as a protective cushion around vital organs, shielding them from physical trauma. • The fat around organs acts as a shock absorber, reducing injury risk.
- 30. LIPID METABOLISM
- 31. LIPID METABOLISM • Lipid metabolism is the process of synthesizing, breaking down, and storing fat in cells for energy storage. • It is a complex process in eukaryotic cells and the basis for forming chemical compounds.
- 32. 1. DIGESTION OF LIPIDS • Lipid breakdown begins in the mouth through lingual lipase from salivary glands. • Gastric lipase breaks down triglycerides into diglycerides and free fatty acids. • In the small intestine, liver-secreted salts emulsify fats for easier digestion. • Pancreatic lipase breaks triglycerides into monoglycerides and free fatty acids. • This process results in micelles, absorbed by small intestine epithelial cells.
- 34. 2. LIPID ABSORPTION AND TRANSPORT • Monoglycerides and fatty acids form micelles in the intestines, absorbed by enterocytes. • Fatty acids and monoglycerides are reassembled into triglycerides inside enterocytes. • Triglycerides are packaged into chylomicrons, transporting lipids into the bloodstream. • Lipoprotein lipase (LPL) breaks down triglycerides into free fatty acids • These are taken up by tissues for energy storage or use.
- 36. 3. LIPID STORAGE AND MOBILIZATION • Triglycerides are transported through the bloodstream and stored in adipose tissue. • Re-esterification of fatty acids into triglycerides in adipocytes. • Enzyme hormone-sensitive lipase (HSL) breaks down stored triglycerides into fatty acids and glycerol during energy demand. This enzymes is activated by hormones such as epinephrine and glucagon. • Free fatty acids are released into the bloodstream, bind to albumin, and are transported to tissues for energy production.
- 39. FATTY ACID OXIDATION • Free fatty acids enter mitochondria for beta-oxidation. • Fatty acids are broken down into acetyl-CoA units, entering the Krebs cycle for energy production. • Acetyl-CoA produces NADH and FADH2, generating ATP. • Excess acetyl-CoA is converted into ketone bodies for alternative energy sources.
- 41. LIPID SYNTHESIS (LIPOGENESIS) • Consumption of excess carbohydrates and proteins can convert them into fatty acids and stored as triglycerides. • This process occurs primarily in the liver and adipose tissue, where glucose is converted into acetyl-CoA and subsequently into fatty acids. • Fatty acids and glycerol combine to form triglycerides, stored in adipose tissue. • Insulin promotes lipogenesis by activating enzymes such as acetyl-CoA carboxylase and fatty acid synthase, which facilitate the conversion of glucose to fatty acids.
- 42. LIPIDS AND HEALTH RISKS
- 43. LIPIDS AND HEALTH RISKS Excessive or imbalanced lipids pose significant health risks. Excessive LDL cholesterol and triglycerides, coupled with low HDL cholesterol, significantly increase the risk of cardiovascular diseases such as heart attacks, strokes, and atherosclerosis. Obesity, diabetes, and unhealthy diets can exacerbate lipid imbalances, leading to further health risks. Monitoring lipid levels and maintaining a balanced diet, rich in healthy fats (unsaturated fats), can help mitigate these risks and support overall cardiovascular and metabolic health.
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