BMS 100 Lipids, Part 1 - Fatty Acid Structures, PDF

Lipids Part 1 – Fatty Acid Structures Dr. Heisel BMS100 Lipid Review Lipids can be broken down structurally into two main classes: § 1) Those based on fatty acid structure § 2) Those based on isoprenoid structure Lipids: Fatty acids Objectives Be able to provide the name of a given fatty acid using...

Lipids Part 1 – Fatty Acid Structures Dr. Heisel BMS100 Lipid Review Lipids can be broken down structurally into two main classes: § 1) Those based on fatty acid structure § 2) Those based on isoprenoid structure Lipids: Fatty acids Objectives Be able to provide the name of a given fatty acid using the two common naming conventions Discuss the differences between cis and trans unsaturated fatty acids Outline the mechanism and regulation of fatty acid synthesis Discuss the importance of essential fatty acids Outline the basic structure and function of the following: Triacylglycerols Provide the mechanism and regulation of synthesis Outline the links between sugar intake and fat storage Phospholipids Discuss the mechanism of synthesis Glycosphingolipids Eicosanoids Waxes Lipids: Fatty acids Outline Naming of fatty acids Fatty acid synthesis Lipids with fatty acid structures Triacylglycerols Phospholipids Glycosphingolipids Eicosanoids Waxes Fatty acids Naming of fatty acids Two naming conventions are commonly used to describe fatty acid structure Examples: 18:4Δ6,9,12,15 and 18:4 (ω-3) Both describe a fatty acid with 4 double bonds in the same place Fatty acids 18:4Δ6,9,12,15 18 = number of carbons 4 = total number of double bonds (db) 6,9,12,15 = first carbon of each db, counting from acid end Fatty acids 18:4 (ω-3) 18 15 12 9 6 3 1 18 = number of carbons 4 = total number of double bonds (db) ω-3 = first carbon of first db, counting from the methyl end Each subsequent db is then 3 carbons away Unlike the previous naming convention, these subsequent carbons are not included in the name Fatty acids 18:4Δ6,9,12,15 and 18:4 (ω-3) are the same fatty acid 15 12 9 6 3 1 Fatty acids Unsaturated fatty acids Double bonds can be cis or trans The cis form creates a “bend” in the structure What do you think this does to membrane fluidity? ie do cis bonds allow for tighter or looser packing of phospholipids? Fatty acids Cis vs trans double-bonds Cis = most naturally made fats Trans = two sources Some made naturally by bacteria in gut of ruminants, so found in meat products FYI: meats are typically less than 6% trans Most made commercially as a by-product of partial hydrogenation https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2596737/ Fatty Acids Class Poll Partial hydrogenation targets cis-bonds in fatty acids to: A) Remove hydrogens and turn oils into solid fats B) Remove hydrogens and turn solid fats into oils C) Add hydrogens and turn oils into solid fats D) Add hydrogens and turn solid fats into oils Why would you want to do this? Fatty acids Cis vs trans double-bonds Trans fats continued By-product of partial hydrogenation is formation of some trans bonds FYI: partially hydrogenated fats can be upto 60% trans How can partially hydrogenated fats be labelled as “0 trans fat” ? Using reduced pressure and blending with oil reduces the trans fat content. Less than 0.5 grams per serving can be labelled as “0% trans fat”. Associated with increased risk of coronary heart disease https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2596737/ https://www.mayoclinic.org/diseases-conditions/high-bloodcholesterol/in-depth/trans-fat/art-20046114 Lipids: Fatty acids Outline Naming of fatty acids Fatty acid synthesis Lipids with fatty acid structures Triacylglycerols Phospholipids Glycosphingolipids Eicosanoids Waxes Fatty acids Fatty acid synthesis Occurs in cytoplasm, typically makes 16:0 palmitate Substrates: Acetyl CoA and malonyl CoA Malonyl CoA is acetyl CoA with an extra CO2 group added CO2 Fatty acids Fatty acid synthesis Enzyme: Fatty acid synthase Enzyme complex, exists as a dimer Two fatty acid chains can be made at once Contains two S groups: one from cysteine, one from B5 Cys binds acetyl groups, B5 binds malonyl groups These will combine to make one chain on each side of the enzyme COOCH3 CH2 C=O S C= O S Cys B5 B5 Cys S S C=O C=O CH2 CH3 COO- Fatty acids CO2 Fatty acid synthesis Coenzymes: B7 (biotin) Helps add CO2 to acetyl CoA to make malonyl CoA What do you think the enzyme name is? B5 As mentioned: part of fatty acid synthase Also part of acetyl CoA and malonyl CoA (as CoA) B3 (NADPH) Reduces the fatty acid chain Review: Which pathway provides the NADPH? Fatty acid synthesis CoASH C * CoASH O C CH3 B5 Cys SH SH 1 1) Acetyl group joins 2) Malonyl group joins B5 SH O CH2 COO- Cys S 2 B5 Cys C=O S C=O S C=O CH3 CH2 CH3 * Only half of dimer shown for simplicity COO- Fatty acid synthesis B5 Cys B5 Cys B5 S C=O S C=O S C=O CH2 CH3 CH2 CH2 C=O CH2 COOCO2 3) Acetyl and malonyl groups condense with loss of CO2 CH3 SH H2O 4) O removed as water, NADPH donates H’s S C=O Cys SH CH3 5) Fatty acid chain shifts over Fatty acid synthesis How do you get to a 16 carbon chain? Keep repeating step 2-4: what are they? B5 2 C SH Cys S C=O 3-4 B5 Cys S SH C=O CH2 CH2 O CH2 CH2 CH2 COO- CH2 CH2 CH3 CH3 Fatty acid synthesis How do you get the chain off the enzyme? Use water to break the bond B5 Cys S SH C=O CH2 OH Hydrolysis C=O CH2 CH2 CH2 CH2 CH2 C H2 CH2 CH3 CH3 From water Fatty acid synthesis How do you make the chain bigger than 16C? Elongate using enzymes embedded in the ER membrane Process follows similar steps, but uses individual enzymes How do you make odd-numbered fatty acid chains? Vast majority of fatty acids are even Starting with propionyl CoA (3 C) rather than acetyl CoA (2 C) in step one can make odd numbered chains 2 Acetyl CoA Propionyl CoA Fatty acid synthesis How do you get unsaturated fatty acids? Some we can make in the ER Desaturase enzymes use NAD(P)H (B3) to create double bonds Stearate (18:O) + NADH + H+ + O2 à oleate (18:1Δ9 ) + NAD+ + 2H2O O2 picks up 2 H’s from stearate and 2 H’s from NADH + H+ Some are “essential”, only get from diet Example: linoleic acid, 18:2 Δ9,12 Δ12 and Δ15desaturase enzymes are only found in plants Fatty acids: Essential Needed to support cardiovascular, immune, reproductive and nervous systems ω-3 ex: α-linolenic acid High levels in fish ω-6 ex: linoleic acid High levels in vegetable oils Too many in relation to ω-3 levels can promote inflammation, increase the risk of heart disease, etc Optimal ratio around 1-4 : 1 for ω-6 : ω-3 Typical Wester diet around 16 : 1 https://pubmed.ncbi.nlm.nih.gov/12442909/ Fatty acid synthesis regulation How do you regulate fatty acid synthesis? With the following hormones: Glucagon – typically released when blood sugars levels are low Insulin – typically released when blood sugar levels are high Epinephrine – released during sympathetic (flight or fight) responses Points to consider: Synthesis is oppositely regulated to breakdown (beta ox) Synthesis promotes storage of fats as TGs Take a few minutes to discuss with your classmates which of the scenarios on the following slide are correct, and justify your answers A) Glucagon promotes fatty acid synthesis (and therefore decreases beta ox) B) Glucagon promotes beta ox (and therefore decreases fatty acid synthesis) C) Insulin promotes fatty acid synthesis (and therefore decreases beta ox) D) Insulin promotes beta ox (and therefore decreases fatty acid synthesis) E) Epinephrine promotes fatty acid synthesis (and therefore decreases beta ox) F) Epinephrine promotes beta ox (and therefore decreases fatty acid synthesis) Fatty acid synthesis regulation Glucagon and epinephrine Inhibit acetyl CoA carboxylase Insulin Activates acetyl CoA carboxylase What does acetyl CoA carboxylase catalyze? Fatty acid synthesis regulation Glucagon and epinephrine Inhibition of acetyl CoA carboxylase, Malonyl CoA Decreased substrate for fatty acids Decreased fatty acid synthesis Increased transport of fatty acids into the mitochondria Increased beta oxidation Fatty acid synthesis regulation Insulin Increased substrate for fatty acids Increased fatty acid synthesis Activation of acetyl CoA carboxylase, Malonyl CoA Decreased transport of fatty acids into the mitochondria Decreased beta oxidation Lipids: Fatty acids Outline Naming of fatty acids Fatty acid synthesis Lipids with fatty acid structures Triacylglycerols Phospholipids Glycosphingolipids Eicosanoids Waxes Fatty acids: Triglycerides Triglycerides (aka triacylglycerols, TAGs, TGs) Three fatty acids attached to a ? backbone via an ? link Provide energy and insulation Review: Which packs tighter and therefore stores energy more efficiently: TG’s or glycogen? Why? Triglyceride Glycogen Fatty acids: Lipogenesis Triglyceride synthesis Lipogenesis Liver and adipocytes: Cytosol or mitochondria? Starts with addition of 2 fatty acids to a glycerol backbone Synthesis of what other lipid molecule also starts this way? Phosphate-alcohol head group Fatty acids: Lipogenesis Lipogenesis steps Make the substrates Glycerol-3-phosphate backbone 3 fatty acyl CoAs Transfer 2 fatty acid chains to the backbone sequentially Replace the phosphate on the backbone with the 3rd fatty acid chain Fatty acids: Lipogenesis Making the backbone review Liver: What enzyme do you think adds a phosphate to glycerol? H2C-OH HO-CH H2C-OH Glycerol ATP ADP H2C-OH HO-CH H2C-OPO3-2 Glycerol-3-phosphate Class Poll: A) Glycerol phosphorylase B) Glycerol phosphotransferase C) Glycerol phosphatase D) Glycerol ATPase E) Glycerol kinase Fatty acids: Lipogenesis Making the backbone review Adipose and liver: Convert DHAP (from where?) to glycerol-3-phosphate using what enzyme? H2C-OH O=C H2C-OH + NADH + H+ H2C-OPO3-2 DHAP HO-CH + NAD+ H2C-OPO3-2 Glycerol-3-phosphate Fatty acids: Lipogenesis Making the fatty acyl CoA’s Fatty acids are added to a CoA carrier using ATP CoA acts to carry the fatty acid chains to the backbone and transfer them over + CoASH Fatty acid ATP Fatty acyl CoA CoA Fatty acids: Lipogenesis Adding the first 2 fatty acid chains to glycerol-3-P O H2C-OH R-C-SCoA HO-CH H2C-OPO3 O H2C-OC-R HO-CH -2 HSCoA O R-C-SCoA Review: What phospholipid is this? H2C-OPO3-2 O Enzyme = acyl transferase HSCoA O H2C-OC-R R-C-O -CH H2C-OPO3-2 Fatty acids: Lipogenesis Removing the P and adding the last fatty acid chain Diacylglycerol Phosphatidic acid O O H2C-OC-R O Enzyme? R-CO -CH H2C-OPO3-2 O H2C-OC-R R-CO -CH P O R-C-SCoA Triacylglycerol H2C-OH O HSCoA Enzyme? O H2C - OC-R R-CO –CH H2C – O-C-R O How can sugar make you fat?!? Discuss the next slide with a partner, answer the questions/fill in the blanks Glucose Glycogen er v i L Glucose-6-P A: What glycolysis intermediate can shunt into lipogenesis? B: What lipogenesis substrate can be made from (A)? Pyruvate Pyruvate Carboxylase D: Activated by? CAC Low energy levels C: What PPS product is used to help make fatty acids? LIPOGENESIS Pyruvate Oxaloacetate Various 5C sugars Pentose P Shunt Acetyl CoA Citrate Fatty Acids Malonyl CoA E: What product of citric acid breakdown is a substrate for fatty acid synthesis? F: Enzyme? - Activated by citrate G: What is the other product of citric acid breakdown? What might the liver do with it ? High energy levels/high [citrate] Citrate Lipids: Fatty acids Outline Naming of fatty acids Fatty acid synthesis Lipids with fatty acid structures Triacylglycerols Phospholipids Glycosphingolipids Eicosanoids Waxes Fatty acid structures Phospholipids and glycosphingolipids both contain: 1) A backbone 2) Lipid (may be part of backbone) 3) Head group Phosphoglycerides Sphingolipids (aka glycerophospholipids) 1) Sphingosine backbone 2) Ceramide: sphingosine (includes a fatty chain), plus an additional fatty acid chain 1) Glycerol backbone 2) 2 fatty acid chains Phosphatidates Sphingomyelin - Phosphatidyl: -serine, -ethanolamine, -inositol, -choline 3) Polar phosphate-alcohol head group PHOSPHOLIPIDS Cerebrosides Gangliosides 3) Carbohydrate head group GLYCOSPHINGOLIPIDS Phospholipids: Phosphoglycerides Synthesis review: H - Where are these made? - What are the first 3 steps? Glycerol-3-P is made from ____ in liver and adipose. Liver can also make it from ____. Fatty acids are activated by attachment to a ____ carrier ____ fatty acids are sequentially added to the glycerol-3-P At this point you have phosphatidic acid – what’s left to do to get other phospholipids? Phospholipids: Phosphoglycerides Synthesis review: Adding the head group First, a CMP is added to create a good leaving group Next, the CMP is removed and head group is attached via nucleophilic substitution CMP Phospholipids: Sphingolipids Sphingomyelin is a PL that is a sphingolipid Same as other PL’s wrt: Phosphate-alcohol head group Different to other PL’S wrt: Backbone = sphingosine (part of ceramide) Similar to other PL’s wrt: Having two fatty acid-like tails, but: One is part of the sphingosine backbone One is added to sphingosine to make a ceramide Found in cell membranes, important component of myelin Sphingolipids Cerebrosides and gangliosides are also sphingolipids Unlike sphingomyelin, they are not phospholipids They are glycosphingolipids Same as sphingomyelin wrt: Sphingosine backbone Ceramide lipid component (sphingosine + fatty acid) Different to sphingomyelin wrt: Headgroups = carbohydrates Gangliosides = 1 or more sialic acid plus 1 or more additional monosaccharides Cerebrosides = monosaccharide head group If additionally sulfated = sulfatide Common in neuronal cell membranes SPHINGOLIPIDS 1 Monosaccharide 1 or more Monosaccharides Phosphocholine Fatty acid Sphingosine (phospholipid) Fatty acid Plus one or more Sialic acid Fatty acid Sphingosine (glycosphingolipid) Sphingosine (glycosphingolipid) Glycosphingolipids Accumulation of sphingolipids leads to sphingolipid storage diseases (sphingolipidases) Most are fatal Tay-Sachs Disease GM2 accumulates in lysosomes due to an enzyme deficiency G = ganglioside M = # of sialic acids (ie one) 2 = pattern of monosaccharides in head group Most severe excesses occur in the brain Build-up leads to neuronal cell damage Progressive neurodegeneration can lead to death by 5 years of age Lipids: Fatty acids Outline Naming of fatty acids Fatty acid synthesis Lipids with fatty acid structures Triacylglycerols Phospholipids Glycosphingolipids Eicosanoids Waxes Fatty acid derivatives Eicosanoids: Derived from arachidonic acid (20:4) or similar 20 C fatty acids Include prostaglandins Physiological functions depend on the type and include: Arachidonic acid Vasodilation Vasoconstriction Platelet aggregation A prostaglandin Fatty acid derivatives Waxes Mixtures of non-polar molecules, including fatty acids linked to long-chain hydrocarbon alcohols via ester bonds Wax esters are found in cerumen (ear wax), beeswax, etc H Fatty acid H Hydrocarbon alcohol Lipids Part 2 – Isoprenoid Structures Dr. Heisel BMS100 Lipid Review Moving on from lipids with fatty acid structure… … to those based on isoprenoid structure Lipids: Fatty acids Objectives Describe the 3 categories of terpenes, including naming conventions and examples Outline the process of cholesterol synthesis Discuss uses for cholesterol and the basic mechanism of familial hypercholesteremia Outline the basic structure and function of plant sterols Categories of Isoprenoids 1) Terpenes Isoprene units linked together Sometimes in alcohol or aldehyde or ring form Smallest terpene = 2 isoprene units linked together = monoterpene Diterpene = 4 isoprenes, triterpene = 6 isoprenes, etc Names of common terpenes Farnescene = a sesqui (?) terpene Squalene = a triterpene Beta carotene = a tetraterpene Categories of Isoprenoids CoQ 1) Terpenes 2) Mixed Terpenes Terpenes with a non-terpene component attached Examples: CoQ (important in ETC) Vit. K (important in clotting) Farnesylated proteins (important in cell signalling) Cys S Vit K Categories of Isoprenoids 1) Terpenes 2) Mixed Terpenes 3) Steroids Review: Complex molecules made from 6 isoprene units Contain four fused rings with various substituents Made from cholesterol Review: Cholesterol synthesis Isoprenoids: Steroids Review: Cholesterol synthesis Starts with 3 of what molecule making which intermediate? Note: This is also the start of ketogenesis What is the rate limiting enzyme? What does high cholesterol do to this enzyme? What class of pharmaceutical drugs inhibit this enzyme? What isoprenoid is formed that is ultimately converted to the cyclic structure of cholesterol? Cholesterol synthesis review 3 X Acetyl CoA To ketogenesis HMG CoA Mevalonate Rate limiting step catalyzed by HMG-CoA reductase Blocked by high cholesterol levels and the cholesterollowering “statin” drugs such as atorvastatin (Lipitor®) Isopentenyl pyrophosphate (isoprene units) Squalene Cholesterol Isoprenoids: Cholesterol Most cholesterol synthesis occurs in the liver The liver can use cholesterol to: Make bile Make lipoproteins (LDL, lipid part includes cholesterol) to carry cholesterol to the tissues LDL binds a receptor on the cell and is internalized LDL is broken down inside the cell, and cholesterol is released Why do the cells want cholesterol? Familial hypercholesteremia is an inherited defect in LDL-receptors Leads to an increase in circulating LDL, and therefore cholesterol, in the blood This increases risk of myocardial infarction Isoprenoids: Cholesterol Cholesterol is a precursor to steroid hormones All animal steroids are derived from cholesterol Cholesterol is first converted to pregnenolone, which is then converted to various other steroid hormones Hormones are made in specific tissues depending on the enzymes that are expressed in those tissues Other steroid hormones Cholesterol Pregnenolone Examples: - Testosterone and estrogen: made in testes and ovaries respectively - Cortisol: made by adrenal glands to regulate stress responses Isoprenoids: Plant sterols Plant sterols have a similar structure to cholesterol Used in plant membranes Can compete with intestinal cholesterol absorption Helps lower LDL cholesterol levels HO Cholesterol Plant Sterol Isoprenoids: Plant sterols Cardiac glycosides are derivatives of plant sterols Note the lipid attached to the carbohydrate: this is an isoprenoid ring structure Review: Digoxin is a cardiac glycoside What does it do to the heart?