University:
Kentucky State University
Course:
CHE 315 | Biochemistry
Academic year:

2020
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201

Pages:

46
Author:

Nossardisd7p

8 Lecture Title :Lipids and Membranes BIOCHEM Lecture Date : 28/4/ 2021 8-1 8 Functions of Lipids • Source of energy • Cellular membranes • Excellent insulators • Thermal insulators • Electrical insulators (in membranes) • Special roles: • Signals • Hormones, Mediators, or growth factors. • Coenzymes • Vitamins 8-4 8 Sheet Note #1 → The main source of energy is lipids. Carbohydrates are immediate source of energy, because we consume glucose and glycogen quickly while lipids take time since they are stored subcutaneously and around the organs. 8-5 8 Lipids • Lipids: a heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties • insoluble in water, but soluble in nonpolar organic solvents including diethyl ether, chloroform, methylene chloride, and acetone • Amphipathic in nature • Lipids include • Open Chain forms • fatty acids, triacylglycerols, sphingolipids, phosphoacylglycerols, glycolipids, • lipid-soluble vitamins • prostaglandins, leukotrienes, and thromboxanes • Cyclic forms • cholesterol, steroid hormones, and bile acids 8-6 8 Sheet Note #2 → Amphipathic means it contains 2 groups one is water soluble and the other (hydrocarbons) is nonsoluble. Cyclic forms =Ring structure Open forms=straight structure Cholesterol will forms the steroidal hormones and the bile acids 8-7 8 Fatty Acids • Fatty acid: an unbranched-chain carboxylic acid, most commonly of 12 - 20 carbons, derived from hydrolysis of animal fats, vegetable oils, or phospholipids of biological membranes • Usually contain even numbers of carbons (can contain odd, depending on how they are biosynthesized) • FA that contain C=C, are unsaturated: If they contain only C-C bonds, they are saturated • Length of fatty acid plays a role in its chemical character 8-8 8 Sheet Note #3 • Even numbers of carbons means that its 12 or 14 or 16 or 18 or 20 8-9 8 8-10 8 Sheet Note #4 • Palmitic acid (palm oil) 16 carbons saturated fatty acid • Steairc acid (animal fat) 18 carbons saturated fatty acid • Oleic acid (olive oil) • Linoleic acid 18 carbons unsaturated fatty acid 18 carbons unsaturated fatty acid (2 double bond) • a- Linolenic acid 18 carbons unsaturated acid (3 double bond) • Archidonic acid 20 carbons unsaturated acid (4 double bond) (all of the above have a carboxyl and a methyl end) 8-11 8 • In most unsaturated fatty acids, the cis isomer predominates; the trans isomer is rare. • Unsaturated fatty acids have lower melting points than their saturated counterparts; the greater the degree of unsaturation, the lower the melting point. 8-12 8 Sheet Note #5 • when the number of carbons increase in a saturated fatty acid, melting point increases. • Cis isomers exist at an angle while the trans are straight 8-13 8 Fatty Acids 8-14 8 Fatty Acids 8-15 8  In the shorthand notation for fatty acids • saturated FA: the number of carbons then (:) then (0) are shown • unsaturated FA: the number of carbons then (:) then the number and location of double bonds in the chain raised above delta symbol (Δ) are shown, separated by a colon • Note: Counting starts from C of COOH • Examples: palmitic (16:0), stearic (18:0), and oleic acids (18:1Δ9) = double bond between C9 and C10 8-16 8 Sheet Note #6 • palmitic (16:0) → 16:0 means it contains 16 carbons and it’s saturated (no double bonds). • stearic (18:0) → 18:0 means it contains 18 carbons and it’s saturated (no double bonds). • pleic acid (18:1Δ9) → mean unsaturated with 18 carbons and a double bond at carbon number 9 8-17 8 Essential Fatty Acids • They have to be supplied in the diet without exception. • They are all polyunsaturated fatty acids: the C20 fatty acid arachidonic acid (20:4 Δ 5,8,11,14) and the two C18 acids linoleic acid (18:2 Δ 9,12) and linolenic acid (18:3 Δ 9,12 ,15 ). • The animal organism requires arachidonic acid to synthesize eicosanoids. 8-18 8 Sheet Note #7 • Fatty acids have 2 ends one is a carboxyl end and the other is a methyl end. • essential fatty acids must be supplied by food similar to the essential amino acids. 8-19 8 • Nutritional fats contain palmitic, stearic, oleic acid, and linoleic acid particularly often. Unsaturated fatty acids are usually found at the central C atom of glycerol. #Sheet note • Glycerol has 3 carbons, the central one contains unsaturated fatty acid (triglycerides) 8-20 8 Omega-3 fatty acid • Also called ω-3 fatty acids or n-3 fatty acids are polyunsaturated fatty acids (PUFAs) with a double bond (C=C) at the third carbon atom from the end of the carbon chain. which is considered the beginning of the chain, thus "alpha", and the methyl (-CH3) end, which is considered the "tail" of the chain, thus "omega"; the double bond is at omega minus 3 (not dash 3). One way in which a fatty acid is named is determined by the location of the first double bond, counted from the methyl end, that is, the omega (ω-) or the n- end. 8-21 8 Sheet Note #8 • Omega 3,6,9… are capsules sold without prescription and people buy a lot of them because they decrease heart disease / cancer and improve the memory and the brain . • (minus3 or -3) means that the double bond is in the third Location from the methyl end and so on for the 6 (-6 Location 6 )and 9(-9 location 9) . 8-22 8 • The three types of omega-3 fatty acids involved in human physiology are α-linolenic acid (ALA) (found in plant oils), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA)(both commonly found in marine oils). Common sources of plant oils containing the omega-3 ALA fatty acid include walnut, edible seeds, seed oil, algal oil, flaxseed oil, while sources of animal omega-3 EPA and DHA fatty acids include fish, fish oils, eggs from chickens fed EPA and DHA, squid oils. Dietary supplementation with omega-3 fatty acids does not appear to affect the risk of death, cancer or heart disease. 8-23 8 Triacylglycerols • Triacylglycerol (triglyceride): an ester of glycerol with three fatty acids • natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH, in a hydrolysis reaction called saponification (Latin, sapo, O soap) O CH2 O- CR R' CO-CH O CH2 O- CR'' A triacylglycerol (a triglyceride) N aOH, H2 O RCOO - N a+ CH2 OH HOCH + CH2 OH 1,2,3-Propanetriol (Gl ycerol, gl yceri n) R' COO- Na + R' ' COO - N a+ Sodi um Soaps 8-24 8 Sheet Note #9 • If we use Triacylglycerols with : 1. NaOH it will produce hard soap. 2. KOH it will produce soft (liquid ) soap. 3. Alcohol it will produce higeen . Triacylglycerols are excess fats stored as Triacylglycerols subcutaneously and around the organs. Triacylglycerols are two types: 1) Simple: glycerol + on fatty acid 2) Mixed: glycerol + different types of fatty acids. (more common) 8-25 8 8-26 8 8-27 8 Soaps • Soaps form water-insoluble salts when used in water containing Ca(II), Mg(II), and Fe(III) ions (hard water) - 2 CH3 ( CH2 ) 1 4 COO Na + + Ca 2+ A sodium soap (soluble in w ater as mi cell es) - [ CH3 ( CH2 ) 1 4 COO ] 2 Ca Cal ci um salt of a fatty aci d (i nsol uble i n water) 2+ + 2 Na + 8-28 8 Hydrolysis of Triglycerides • Chemical hydrolysis, by saponification as mentioned earlier • Enzymatic digestion by lipase enzyme 8-29 8 Sheet Note #10 • lipase is a pancreatic enzyme. • pancreas works on carbohydrates by a- amylase enzyme and on proteins by trypsin , chymotrypsin , elastase enzymes and on lipids by lipase enzyme to give fatty acids and glycerol. 8-30 8 Phosphoacylglycerols • Phosphoacylglycerols (= phospholipids) are the second most abundant group of naturally occurring lipids • found almost exclusively in plant and animal cell membranes, which typically consist of 40% -50% phosphoacylglycerols and 50% - 60% proteins • the most abundant phosphoacylglycerols are derived from phosphatidic acid, a molecule in which glycerol is esterified with two molecules of fatty acid and one of phosphoric acid • the three most abundant fatty acids in phosphatidic acids are palmitic (16:0), stearic (18:0), and linoleic (18:1) 8-31 8 Phosphatidic acid 8-32 8 Phosphatidic acid 8-33 8 Phosphatidic acid palmi tic aci d O gl ycerol O CH2 O CH steari c acid O OCH2 -O- P-O O 8-34 8 Phosphatidyl esters • Further esterification with a lowmolecular-weight alcohol with phosphate group gives a phosphoacylglycerol or phosphatidyl ester • the most common of these lowmolecular-weight alcohols are: 8-35 8 Phosphatidyl esters 8-36 8 Phosphatidyl esters Name and Formula Name of Phospholipid ethanolamine HOCH2 CH 2 NH 2 phosphatidylethanolamine (cephal in) choline phosphatidylchol ine (l ecithin) seri ne HOCH2 CHCOO phosphatidylseri ne + HOCH2 CH 2 N( CH3 ) 3 NH3 The most common + 8-37 8 Phosphatidyl esters inositol HO HO OH OH phosphatidylinositol OH OH gl ycerol OH HOCH2 CH CH 2 OH phosphatidylglycerol OH O phosphatidylgl ycerol di phosphatidyl glycerol O (cardiolipin) HOCH2 CH CH 2 OPOCH2 CHOCR3 O- CH2 OCR4 O 8-38 8 Phosphatidyl esters • A lecithin steari c acid choline O O + O P OCH 2 CH 2 N( CH 3 ) 3 OCH 2 O CH O CH 2 palmi tic acid gl ycerol O 8-39 surfactant 8MolecularPulmonary Dynamics simulation of DPPC lipid bilayer formation in two phase systems reduces surface tension #note it surrounds the alveoli of the lungs so exhalation and inspiration become easier 8-40 8 Diagram of the alveoli with both cross-section and external view 8-41 8 Respiratory Distress Syndrome Result from the Disruption of Lipid Metabolism Respiratory distress syndrome is a pathological condition resulting from a failure in the biosynthetic pathway for dipalmitoyl phosphatidyl choline. This phospholipid, in conjunction with specific proteins and other phospholipids, is found in the extracellular fluid that surrounds the alveoli of the lung, where it decreases the surface tension of the fluid to prevent lung collapse at the end of the expiration phase of breathing. Premature infants may suffer from respiratory distress syndrome because their immature lungs do not synthesize enough dipalmitoyl phosphatidyl choline ( Surfactant ). 8-42 8 Waxes • A complex mixture of esters of long-chain carboxylic acids and alcohols • Found as protective coatings for plants and animals 8-43 8 Sheet Note #11 • Waxes surround insects and some tree leaves to protect them from water and rains . • Myricyl is artificial and use for car and shoes polish 8-44 8 Sphingolipids • Contain sphingosine, a long-chain (18 C) aminoalcohol from which this class is named • Found in plants and animals • Abundant in nervous system Surround the nerve choline 8-45 8 Glycolipids • Glycolipid: a compound in which a carbohydrate is bound to an -OH of the lipid • many glycolipids are derived from ceramides • Ceramide + simple sugar= cereboside (found in nerves and brain cells) 8-46 8 8-47 Fig. 8-8, p.190 8 Tay-Sachs disease It is caused by a failure of lipid degradation: an inability to degrade gangliosides. Gangliosides are found in highest concentration in the nervous system, particularly in gray matter, where they constitute 6 % of the lipids. Gangliosides are normally degraded inside lysosomes by the sequential removal of their terminal sugars but, in Tay-Sachs disease, this degradation does not occur. As a consequence, neurons become enormously swollen with lipid-filled lysosomes . An affected infant displays weakness and retarded psychomotor skills before 1 year of age. The child is demented and blind by age 2 and usually dead before 8-48 age 3.

Lipids and Membranes

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