BCH3033 Biochemistry 1 Chapter 10a PDF

BCH3033: Biochemistry 1 Chapter 10 a 03.13.2024 Donella Beckwith, Ph.D. [email protected] 1 Fats and Oils Used as Stored Energy Are Derivatives of Fatty Acids fatty acids: – Hydrocarbon derivatives Carboxylic acids with hydrocarbon tails ranging from 4 to 36 carbons in length (C4 to C36) Branched or...

BCH3033: Biochemistry 1 Chapter 10 a 03.13.2024 Donella Beckwith, Ph.D. [email protected] 1 Fats and Oils Used as Stored Energy Are Derivatives of Fatty Acids fatty acids: – Hydrocarbon derivatives Carboxylic acids with hydrocarbon tails ranging from 4 to 36 carbons in length (C4 to C36) Branched or unbranched Saturated or unsaturated – Water insoluble – Rich source of stored chemical energy for cells Oxidation of fatty acids (to CO2 and H2O) is highly exergonic (thermodynamics) 2 Saturated –vs- Unsaturated Fatty Acids fatty acids: cis and/or trans saturated or unsaturated – saturated: mainly solid at RT – unsaturated: liquid at RT 3 Question 1 Fatty acids: A. can be branched or unbranched. B. are highly oxidized storage forms of hydrocarbons. C. are referred to as “saturated” if they have one or more C–C double bonds. D. never exceed 20 carbons in length, by definition. 4 Naturally Occurring Fatty Acids 5 Naturally Occurring Fatty Acid Examples n-Tetradecanoic acid – 14:0 carbon skeleton cis-,cis-9,12-Octadecadienoic acid – 18:2 carbon skeleton – Δ9, 12 cis-9-Octadecenoic acid – 18:1 carbon skeleton – Δ9 6 Common Patterns in Fatty Acids most common fatty acids have even numbers of carbon atoms in an unbranched chain of 12 to 24 carbons in monounsaturated fatty acids, the double bond is usually between C-9 and C-10 (∆9) in polyunsaturated fatty acids: – the double bonds are usually ∆12 and ∆15 – double bonds are usually separated by a methylene group double bonds are usually in the cis configuration 16:0 9 18:1 12 18:2 7 Question 2 Which statement regarding linoleic acid [18:2(∆9,12)] is false? A. B. C. D. It has one carboxylic acid functional group. It has two double bonds. It has 20 carbons. It has a C–C double bond between carbons 9 and 10. 8 Polyunsaturated Fatty Acids (PUFAs) polyunsaturated fatty acids (PUFAs) = contain more than one double bond in their backbone – omega-3 (ω-3) fatty acids = double bond between C-3 and C-4 relative to the most distant carbon (ω) – omega-6 (ω-6) fatty acids = double bond between C-6 and C-7 relative to ω (example: linoleic and arachidonic acid) Polar & ionized at neutral pH omega-3 (ω-3) fatty acid 9 PUFAs and Human Nutrition humans must obtain the omega-3 PUFA α-linolenic acid (ALA; 18:3(∆9,12,15)) from their diet humans use ALA to synthesize: – eicosapentaenoic acid (EPA; 20:5(∆5,8,11,14,17)) – docosahexaenoic acid (DHA; 22:6(∆4,7,10,13,16,19)) the optimal dietary ratio of omega-6 to omega-3 PUFAs is between 1:1 and 4:1 10 Triacylglycerols Are Fatty Acid Esters of Glycerol triacylglycerols = simplest lipids constructed from fatty acids – composed of three fatty acids, each in ester linkage with a single glycerol – can be simple (one kind of fatty acid) or mixed (two or three different fatty acids) – hydrophobic Nonpolar 11 Question 3 Triacylglycerols: A. always have at least one fatty acid with a trans double bond. B. consist of glycerol and three different fatty acids. C. consist of glycerol and three identical fatty acids. D. are a major energy storage form. 12 Fatty Acids Solubility poor solubility in water due to the nonpolar hydrocarbon chain – increased chain length decreases solubility – decreased double bond number decreases solubility More soluble Less soluble 13 Melting Points of Fatty Acids stearic acid oleic acid at room temperature: – saturated fatty acids have a waxy consistency – unsaturated fatty acids are oily liquids extent of packing depends on degree of saturation – van der Waals 14 Tight packing Triacylglycerols Provide Stored Energy and Insulation vertebrates store triacylglycerols as lipid droplets in adipocytes (fat cells) plants store triacylglycerols in the seeds 15 Lipases Lipases: enzymes that catalyze the hydrolysis of stored triacylglycerols, releasing fatty acids for export to sites where they are required as fuel – adipocytes and germinating seeds contain lipases 16 Question 4 Where do we store triacylglycerol (triglyceride)? A. B. C. D. in the lumen of the ER in the mitochondria in the lipid droplet in the nucleus 17 Advantages to Using Triacylglycerols as Stored Fuels two significant advantages: – because carbon atoms of fatty acids are more reduced than those of sugars, oxidation of fatty acids yields more energy – because triacylglycerols are hydrophobic and unhydrated, the organism does not have to carry the extra weight of water hydration that is associated with stored polysaccharides 18 Triacylglycerols Provide Insulation seals, walruses, penguins, and other warm-blooded polar animals are amply padded with triacylglycerols – provides insulation against low temperatures hibernating animals (e.g. bears) accumulate huge fat reserves before hibernation – provides insulation and energy storage 19 Question 5 What is the advantage of storing energy in the form of triacylglycerol over glycogen? A. Triacylglycerol has a lower melting temperature. B. Glycogen hydrolysis is poorly regulated. C. Because triacylglycerol is bigger, it takes up more space inside the cell. D. Because triacylglycerol is hydrophobic and excludes water, it takes up less space. 20 Partial Hydrogenation of Cooking Oils Improves Their Stability but Creates Fatty Acids with Harmful Health Effects natural fats are complex mixtures of simple and mixed triacylglycerols solid solid 21 Partial Hydrogenation oxidative cleavage of double bonds in unsaturated fatty acids to aldehydes and carboxylic acids causes lipid-rich food to become rancid partial hydrogenation = process that converts many of the cis double bonds in the fatty acids to single bonds – improves shelf life and increases stability – increases the melting temperature – converts some cis double bonds to trans double bonds *Decrease double bonds = decrease solubility 22 Trans Fatty Acids (“Trans Fats”) dietary intake of trans fatty acids is linked to a higher incidence of cardiovascular disease trans fatty acids: – raise the level of triacylglycerols in the blood – raise the level of LDL (“bad”) cholesterol in the blood – lower the level of HDL (“good”) cholesterol – increase the body’s inflammatory response 23 Waxes Serve as Energy Stores and Water Repellents biological waxes = esters of long-chain (C14 to C36) saturated and unsaturated fatty acids with long-chain (C16 to C30) alcohols – higher melting point than triacylglycerols – water-repellant properties – firm consistency 24 Question 6 Which statement is false? A. Naturally occurring fatty acids usually have an even number of carbons. B. Wax esters contain long chain fatty acids and long chain alcohols. C. Triacylglycerols are polar due to their ester functional groups. D. The number of C–C double bonds in a fatty acid affects its melting point. 25 Biological Membranes biological membranes: double layer of lipids that acts as a barrier to polar molecules and ions membrane lipids: – amphipathic = one end of the molecule is hydrophobic, the other hydrophilic – hydrophobic regions associate with each other – hydrophilic regions associate with water 26 Four General Types of Membrane Lipids Phospholipids: have hydrophobic regions composed of two fatty acids joined to glycerol or sphingosine glycolipids = contain a simple sugar or a complex oligosaccharide at the polar ends archaeal tetraether lipids = have two very long alkyl chains ether-linked to glycerol at both ends sterols = compounds characterized by a rigid system of four fused hydrocarbon rings 27 Some Common Types of Storage and Membrane Lipids 28 Glycerophospholipids Are Derivatives of Phosphatidic Acid glycerophospholipids (phosphoglycerides) = membrane lipids in which two fatty acids are attached in ester linkage to the first and second carbons of glycerol, and a highly polar or charged group is attached through a phosphodiester linkage to the third carbon 29 Glycerol is Prochiral attachment of phosphate at one end of glycerol converts it to a chiral compound – named using the D, L system 30 Question 7 Glycerophospholipids do NOT contain: A. B. C. D. fatty acids ester linkages glycerol a mono- or disaccharide 31 Glycerophospholipids Are Named as Derivatives of Phosphatidic Acid a phosphodiester bond joins the head group to glycerol the phosphate group can bear a negative, neutral, or positive charge 32 The Fatty Acids in Glycerophospholipids can be any of a wide variety in general, glycerophospholipids contain: – a C16 or C18 saturated fatty acid at C-1 – a C18 or C20 unsaturated fatty acid at C-2 – C-1 and C-2 are initially hydroxyls that are esterified to fatty acids C-1 C-2 33 Some Glycerophospholipids Have Ether-Linked Fatty Acids ether lipids = one of the two acyl chains is attached to glycerol in ether, rather than ester, linkage – chain may be saturated – chain may contain a double bond between C-1 and C-2 as in plasmalogens 34 Platelet-Activating Factor platelet-activating factor: an ether lipid that serves as a potent molecular signal – releases from leukocytes called basophils – stimulates platelet aggregation and serotonin release – plays a role in inflammation and the allergic response 35 Galactolipids of Plants and Ether-Linked Lipids of Archaea Are Environmental Adaptations galactolipids: member of the glycolipids group that predominate in plant cells – one or two galactose residues are connected by a glycosidic linkage to C-3 of a 1,2-diacylglycerol 36 Question 8 Which statement is false? A. Glycerophospholipids are named as derivatives of the parent compound, phosphatidic acid. B. Ether lipids may be saturated or contain a double bond. C. Platelet-activating factor is a glycerophospholipid. D. The stroma of the chloroplast is rich in galactolipids, composed of a diacylglycerol with one or two linked galactose residues. 37 Sphingolipids Are Derivatives of Sphingosine sphingolipids = large class of membrane phospholipids and glycolipids – have a polar head group and two nonpolar tails – contain no glycerol – contain one molecule of the long-chain amino alcohol sphingosine or one of its derivatives will discuss on next slides 38 Ceramides Are The Structural Parent of All Sphingolipids C-1, C-2, and C-3 of sphingosine are structurally analogous of the three carbons of glycerol in glycerophospholipids Ceramide: compound resulting when a fatty acid is attached in amide linkage to the –NH2 on C-2 – structurally similar to a diacylglycerol 39 Question 9 __________________ a parent compound or compounds of sphingolipids. A. B. C. D. Phospholipases are Glycerol-3-phosphate is Sphingomyelins are Ceramides are 40 Sphingomyelins Sphingomyelins: subclass of sphingolipids that contains phosphocholine or phosphoethanolamine as their polar head group 41 Glycosphingolipids Glyco-sphingolipids: have head groups with 1+ sugars connected directly to the –OH at C-1 of the ceramide moiety – do not contain phosphate – occur largely in the outer face of plasma membranes 42 Cerebrosides and Globosides cerebrosides = have a single sugar linked to ceramide – those with galactose are found in the plasma membranes of cells in neural tissue – those with glucose are found in the plasma membranes of cells in nonneural tissues globosides = glycosphingolipids with 2+ sugars, usually Dglucose, D-galactose, or N-acetyl-D-galactosamine sometimes called neutral glycolipids, as they have no charge at pH 7 43 Gangliosides. gangliosides = have oligosaccharides as their polar head groups and 1+ residues of N-acetylneuraminic acid (Neu5Ac), a sialic acid, at the termini – 1 sialic acid residue = GM (M for mono-) series – 2 sialic acid residues = GD (D for di-) series – 3 sialic acid residues = GT (T for tri-) series (and so on) 1 9 6 8 2 7 4 5 3 44 Question 10 Which sphingolipids have a single monosaccharide as a component? A. B. C. D. cerebrosides gangliosides globosides plasmalogens 45 Sphingolipids at Cell Surfaces Are Sites of Biological Recognition prominent in the plasma membranes of neurons human blood groups (O, A, B) are determined in part by the oligosaccharide head groups of these glycosphingolipids Galactose Fucose GlcNAc Glucose GalNAc Gal 46 Phospholipids and Sphingolipids Are Degraded in Lysosomes phospholipases of the A type remove one of the two fatty acids – lysophospholipases remove the remaining fatty acid (not shown) lysosomal enzymes catalyze the stepwise removal of sugar units of gangliosides (not shown) 47 Question 11 What are the products of phospholipase D degradation of phosphatidylethanolamine? A. B. C. D. diacylglycerol and phosphocholine diacylglycerol and phosphoethanolamine phosphatidate and ethanolamine phosphatidate and choline 48 Abnormal Accumulations of Membrane Lipids genetic defects in any of the hydrolytic enzymes leads to the accumulation of gangliosides in the cell Electron micrograph of a portion of brain cell showing abnormal ganglioside deposits in lysosomes (Tay-Sachs disease) 49 Abnormal Accumulations of Membrane Lipids 50