Questions and Answers
What is the main characteristic of cholesterol?
What is the main difference between fats and oils?
Where does the majority of lipid digestion occur?
What is the role of bile in lipid digestion and absorption?
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What is the final step in the digestion and absorption of lipids?
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What is the structure of the nucleus in cholesterol?
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What is the main function of lipids in the body?
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What is the classification of lipids based on their function?
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What is the general formula of fatty acids?
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What is the characteristic of saturated fatty acids?
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What is the type of lipid formed by esterification of 3 fatty acids to a glycerol molecule?
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What is the main component of cell membrane?
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What is the function of sphingomyelin?
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What is the characteristic of glycolipids?
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What is the primary function of bile salts in digestion?
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What is the function of lipoproteins?
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What is the characteristic of steroids?
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What is the structure of micelles?
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What are the three substances produced from acetyl CoA?
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What is the function of cholesterol in the assembly of cell membranes?
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What is the function of emulsifiers in the digestive tract?
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What is the primary function of steroid hormones?
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What are eicosanoids?
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What is the primary function of leukotrienes?
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What is the function of biological waxes?
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What is the fate of triglycerides in the adipose tissue during starvation states?
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Study Notes
Lipids: Functions and Classifications
- Lipids are organic compounds that are insoluble or sparingly insoluble in water but soluble in organic solvents.
- Functions of lipids:
- Provide a major way of storing chemical energy and carbon atoms in the body.
- Surround and insulate vital body organs, providing protection from mechanical shock and preventing excessive loss of energy.
- Found in living organisms in various forms.
Classification of Lipids
- According to function:
- Triglycerides: storage form of energy.
- Phospholipids and cholesterol: structural components of biomembranes.
- Steroid hormones: metabolic regulators.
- Amphipathic lipids: surfactants, detergents, and emulsifying agents.
- Electric insulators in neurons.
- Subcutaneous fats: provide insulation against changes in external temperature.
- Give shape and contour to the body.
- Cushioning effect.
- Help in the absorption of fat-soluble vitamins (A, D, E, and K).
- According to structure:
- Simple lipids: esters of fatty acids with glycerol or higher alcohols.
- Compound lipids: fatty acids esterified with an alcohol and containing other groups.
- Phospholipids: contain phosphoric acid.
- Non-phosphorylated lipids.
- Derived lipids: derived from lipids or precursors of lipids.
- Fatty acids.
- Steroids.
Fatty Acids
- Fatty acids are simple linear chains of C-H bonds with a carboxyl group (COOH) and a methyl group at the end.
- Classification of fatty acids based on the number of carbon atoms:
- Long-chain fatty acids (C12-C26).
- Medium-chain fatty acids (C8-C12).
- Short-chain fatty acids (C4-C6).
- R-CO-OH is the general formula of fatty acids.
- Physical properties of fatty acids:
- Water solubility: solubility decreases as the carbon chain length increases.
- Melting points:
- Strongly influenced by carbon chain length and the number of double bonds.
- Melting point increases as the carbon chain increases.
- The greater the number of double bonds, the less the melting point.
Types of Fatty Acids
- Saturated fatty acids:
- Fatty acids without double bonds in the entire hydrocarbon chain.
- Ends with "-anoic acid".
- Unsaturated fatty acids:
- Fatty acids with one or more double bonds in the entire hydrocarbon chain.
- Ends with "-enoic acid".
- Types of unsaturated fatty acids:
- Monounsaturated fatty acids.
- Polyunsaturated fatty acids.
Simple Lipids: Triacylglycerols
- Triacylglycerols are the simplest and most abundant type of lipid.
- Found primarily in adipocytes.
- More efficient than glycogen:
- Large quantities can be packed into small volumes.
Compound Lipids: Phospholipids
- Phospholipids are components of cell membranes (lipid bilayer).
- Have an alcoholic backbone with 2 esterified fatty acids (non-polar tail) and a phosphate group (polar head).
- Amphipathic:
- Polar head extends to the exterior (aqueous environment).
- Non-polar head moves toward the interior of the membrane.
Glycolipids
- Same structure as sphingomyelin except that it contains a carbohydrate (polar group) on the first carbon atom of the ceramide molecule and has no phosphate group.
- Essential component of biological membranes, with the highest concentration found in nerve tissue.
- Depending on the nature of the carbohydrate, 4 types can be recognized:
- Cerebroside.
- Sulfatides.
- Globosides.
- Gangliosides.
Lipoproteins
- Complex of lipid and protein.
- Act as lipid transporters.
- 4 major types:
- Chylomicrons.
- VLDL (very low-density lipoprotein).
- LDL (low-density lipoprotein).
- HDL (high-density lipoprotein).
Derived Lipids: Steroids
- Steroids are complex lipid molecules consisting of 17 carbon atoms bonded in four fused rings.
- Classified as lipids because they are hydrophobic and insoluble in water, but do not resemble lipids in terms of structure.
- Cholesterol is the most common sterol in mammals.
Cholesterol
- Classified as a lipid because it is hydrophobic and insoluble in water, but does not resemble lipids in terms of structure.
- May exist as free or esterified form.
- Precursor for 3 useful compounds: bile acid, steroid hormones, and vitamin D.
- Essential component of all biological membranes.
- Component of nerve fibers.
Fats and Oils
- Fats are triacylglycerol mixtures that are solid or semi-solid at room temperature.
- Oils are triacylglycerol mixtures that are liquid at room temperature.
- Obtained from animal sources (fats) or plant sources (oils).
Digestion and Absorption of Fats
- Mouth: water-based salivary enzymes have little to no effect on triacylglycerols.
- Stomach: small amount of lipid digestion occurs due to gastric lipase.
- Liver: bile produced in the liver, stored in the gallbladder, and released into the small intestine to aid in digestion and absorption of lipids.
- Pancreas: pancreatic lipase produced in the pancreas is released into the small intestine.
- Small intestine: products from fat digestion and bile acids form micelles and move to the microvilli to allow lipids to diffuse into mucosal cells.
Bile Salts
- Sodium glycocholate and sodium taurocholate: lower surface tension.
- Emulsify fat droplets and increase surface activity for enhancement of enzyme activity.
Micelles
- Circular in structure.
- Characterized by non-polar tails situated inside and bile acids found outside.
- Hydrophilic exterior and hydrophobic interior.
- Essential for absorption of fat-soluble vitamins (A, D, E, and K).
Chylomicrons
- Absorbed triglycerides are transported in the blood as chylomicrons.
- Taken up by the adipose tissue and liver.
- During starvation states, triglycerides in the adipose tissues are hydrolyzed and produce free fatty acids.
Ketone Bodies
- Produced from acetyl CoA when an excess of acetyl CoA from fatty acid degradation accumulates due to triglyceride-carbohydrate metabolic imbalances.
- Three substances produced: acetone, beta-hydroxybutyric acid, and acetoacetic acid.
Cholesterol and Cholesterol Esters
- Cholesterol is an unsaturated steroid alcohol containing 4 rings with a single C-H side chain tail attached to a fatty acid.
- Amphipathic.
- Found on the surface of lipid layers and synthesized in the liver.
- Functions:
- Precursor of 5 major classes of steroids: progestins, glucocorticoids, mineralocorticoids, androgens, and estrogens.
- Important constituent in the assembly of cell membranes and bile acids.
Emulsification of Lipids: Bile Acids
- Bile acid: cholesterol derivative that functions as a lipid-emulsifying agent in the aqueous environment of the digestive tract.
- Bile: fluid containing emulsifying agents that is secreted by the liver, stored in the gallbladder, and released into the intestine during digestion.
Steroid Hormones
- Hormones: biochemical substances produced by ductless glands that have a messenger function.
- Steroid hormone: hormone that is a cholesterol derivative.
- Sex hormones:
- Estrogens: synthesized in the ovaries and adrenal cortex; development of female secondary sex characteristics and regulation of menstrual cycle.
- Androgens: synthesized in the testes and adrenal cortex; regulation of male secondary sex characteristics.
- Progestins: synthesized in the ovaries and placenta; prepares the lining of the uterus for implantation of a fertilized egg.
- Adrenocorticoid hormones:
- Mineralocorticoids: balance of Na and K ions; aldosterone.
- Glucocorticoids: regulation of glucose metabolism; cortisol.
Eicosanoids
- Oxygenated C20 fatty acid derivative that functions as a messenger lipid.
- Precursor: arachidonic acid.
- Physiological effects:
- Inflammatory response.
- Production of pain and fever.
- Regulation of blood pressure.
- Induction of blood clotting.
- Control of reproductive functions.
- Regulation of sleep/wake cycle.
- 3 principal types of eicosanoids:
- Prostaglandins: contain cyclopentane ring and oxygen-containing functional groups; involved in many regulatory functions.
- Thromboxanes: contain cyclic ether ring and oxygen-containing functional groups; promotes formation of blood clots, produced by platelets.
- Leukotrienes: contain 3 conjugated double bonds and hydroxy group; found in leukocytes.
Biological Waxes
- Lipids that are monoesters of a long-chain fatty acid and long-chain alcohols.
- Protect hair and skin.
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Description
Learn about lipids, also known as fats, and their roles in storing energy, protecting body organs, and being insoluble in water. This quiz covers the basics of lipids in living organisms.
