chem 1152: ch. 18 lipids. lipids biomolecules defined in terms of solubility: – insoluble in water...
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LipidsLipids• Biomolecules defined in terms of solubility:
– Insoluble in water but soluble in nonpolar solvents.– Waxy, greasy or oily compounds.
• Biological Functions:– Energy Storage– Structural component of cell membranes– Signaling molecules
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Two major classes
Saponifiable LipidsSaponifiable LipidsSaponification: base hydrolysis of esters to produce carboxylic acid salt and alcohol
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Simple Lipids:– Contain fatty acids and alcohols
• Complex Lipids:– Contain multiple fatty acids,
alcohol, something else
Fatty AcidsFatty Acids• Building blocks of many lipids• Long chain carboxylic acids• Carboxyl group hydrophilic at physiological pH (7.4)
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
MicellesMicelles
• In aqueous solutions, ionized fatty acids form spherical clusters– Polar head is facing out towards water (hydrophilic)– Long alkane chains associate in interior (hydrophobic) through weak dispersion forces
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Characteristics of Fatty AcidsCharacteristics of Fatty Acids
1. Straight chain (unbranched) carboxylic acids2. Comprised of 10-20 carbons3. Usually have even number of carbons4. Can be saturated or unsaturated5. Usually no other functional groups
• Unsaturated fatty acids usually contain double bonds in the cis configuration
• This creates kink or bend in chain that prevents unsaturated fatty acids from packing together closely unlike saturated fatty acids– Results in weaker intermolecular forces, lower MP’s – Usually liquid at room temp
O
O-
CH3
CH3
O
O-
unsaturated
saturated
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Properties of Unsaturated Fatty AcidsProperties of Unsaturated Fatty Acids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• The kink or bend in chain of unsaturated fatty acids prevents from packing together closely unlike saturated fatty acids– Results in weaker intermolecular forces, lower MP’s – Increases fluidity of biological membranes
Properties of Unsaturated Fatty AcidsProperties of Unsaturated Fatty Acids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Phospholipids form bilayer in cell membrane
Essential Fatty AcidsEssential Fatty Acids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• The human body can synthesize all but two of the necessary fatty acids• Linoleic acid (omega-6 fatty acid)• Linolenic acid (omega-3 fatty acid)
• Must be obtained from diet (plant and fish oils)• Polyunsaturated (multiple double bonds) • 18 Carbons in chain
Diets rich in omega-3 fatty acids may:decrease serum cholesterol, triglycerides reduce risk of heart disease
Fish Nuts Kidney Beans
Sources of omega-3 fatty acids: Spinach Broccoli and cauliflower Oils
Structures of Fats and OilsStructures of Fats and Oils
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Fats: Triglycerides from animal (saturated)• Oils: Triglycerides from vegetables
(unsaturated)• These are esters (alcohol + acid)• Alcohol derived from glycerol• Acid from fatty acids
Most common
lipids
triglyceride
Reactions of TriglyceridesReactions of Triglycerides
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
hydrolysis
saponification
hydrogenation
triglyceride
Ester of 3 alcohols, 3
acids
Chemical Properties of Fats and OilsChemical Properties of Fats and Oils
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Triglycerides exhibit chemical properties of esters and alkenes
Rxn: Hydrolysis
Breakdown of cellular fats to supply energy begins with lipase catalyzed hydrolysis reaction
Chemical Properties of Fats and OilsChemical Properties of Fats and Oils
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Rxn: Saponification
Soapmaking (up to AD 500), by adding base (lye or aqueous extract of wood ash) to animal fat
Chemical Properties of Fats and OilsChemical Properties of Fats and Oils
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Rxn: Hydrogenation
Results in partial hydrogenation (partially-hydrogenated vegetable oils) Semi-solids that don’t separate Crisco
WaxesWaxes
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Simple, saponifiable lipids (long chain fatty acid + alcohol = ester)• Alcohol derived from long chain alcohols (12-32 carbons) not glycerols• Water insoluble• Occur in nature as protective coatings on:
• Feathers• Fur• Skin• Leaves• Fruits
Beeswax
PhosphoglyceridesPhosphoglycerides
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Complex lipids• Serve as major components of cell membranes• Also known as phospholipids• Structure similar to triglycerides
triglyceride
phosphoglyceride
PhosphoglyceridesPhosphoglycerides
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• The most common phosphoglycerides have choline, ehanolamine, or serine attached to the phosphate group.
PhosphoglyceridesPhosphoglycerides
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Lecithins•Phospholglycerides that contain choline•Soy lecithin used to provide smooth texture to margarine, chocolate
Cephalins•Phospholglycerides that contain ethanolamine or serine
Functions: •structural components of cell membranes •micelle forming agents
Functions:•Cell membranes•Blood-clotting
Phosphatidylcholine (lecithin) Cephalin
SphingolipidsSphingolipids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Complex lipid found in cell membrane• Contain sphingosine instead of glycerol• These are found in brain and nerve tissue, and in myelin sheath that
surrounds nerves
GlycolipidsGlycolipids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Another type sphingolipid• Contain carbohydrates• AKA cerebrosides due to abundance in brain tissue• No phosphate linkage
Related DiseasesRelated Diseases
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Some human diseases are related to abnormal accumulation of sphingomyelins and glycolipids
Fluid-mosaic Model of Biological MembranesFluid-mosaic Model of Biological Membranes
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
• Cell membranes for both prokaryotic and eukaryotic cells comprised of lipids organized in a bilayer
SteroidsSteroids
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Exhibit feature of other lipids (e.g., soluble in non-polar solvents) Cholesterol is most abundant steroid in human body
Essential component of cell membranes Precursor for other steroids:
Bile salts Sex hormones Vitamin D Adrenocorticoid hormones
Synthesized in liver or obtained from food May contribute to atherosclerosis
CH3
CH3
CH3
CH3
OH
CH3
Steroid Cholesterol
Bile SaltsBile Salts
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://www.medicinenet.com/gallstones/article.htm
Yellow-brown or green liver secretion stored in gallbladder
Bile salts are released into intestine to separate large globules of lipids into smaller droplets
Bile salts also emulsify (mix immiscibles) cholesterol found in the bile for excretion
Gallstones may occur if cholesterol too high and/or bile salts too low
Steroid HormonesSteroid Hormones
http://schoolworkhelper.net/2010/07/the-endocrine-system-function-and-structure/
Hormone: Chemical produced in the cell or gland that delivers a message affecting cells in another part of the organism
Steroid hormones derived from cholesterol Two Major Steroid Hormones:
Adrenocorticoid Hormones Male and Female Sex Hormones
Steroid hormones diffuse through the cell membrane and combine with receptor proteins in the cytoplasmHormone-receptor complex cause cell to respond to hormone by interacting with cell DNA and stimulating protein synthesis
CH3
CH3
CH3
CH3
OH
CH3
Adrenocorticoid HormonesAdrenocorticoid Hormones
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Produced in adrenal glands located at top of kidneys Classified into 2 functional groups: Mineralocorticoids: Regulate concentration of ions (Na+) in body fluids
Aldosterone: most important mineralocorticoidPromotes absorption of Na+ and Cl- in kidney tubules
Glucorticoids: Enhance carbohydrate metabolism Cortisol is major glucocorticoid in human body Increases glucose and glycogen concentration in body Cortisol, cortisone and prednisolone exert anti-inflammatory effects
Used to treat rheumatoid arthritis, bronchial asthma
Male Sex HormonesMale Sex Hormones
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://artofamandanelson.blogspot.com/2011/09/generating-topics-steroids.html
Male sex hormones (androgens) produced in testes Testosterone: Most important
Promotes normal growth of male genitalia and aids in development of secondary sex characteristics
Anabolic steroids banned for use by athletes include testosterone and derivatives
Use of these can lead to:Liver tumorsTesticular atrophyDecreased sperm count
Female Sex HormonesFemale Sex Hormones
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
Female sex hormones promote development of secondary sex characteristics Increase in voice pitch Increased breast size Inhibition of facial hair
Estrogens: Primary female sex hormones, play important roles in reproduction:
Estradiol Estrone Progesterone
ProstaglandinsProstaglandins
Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011
First identified in secretions from male prostate gland Currently about 20 known prostaglandins in both men and women Cyclic compounds derived from arachidonic acid Hormone-like
Functions:Regulate menstruationPrevent conceptionInduce uterine contractions during childbirth
Therapeutic applications:Induce laborTreat asthmaTreat peptic ulcers