Lecture 8 Lipids PDF

Lipids  Lipids: Structurally Diverse Class Organic molecules that are characterized by low solubility in water => relatively hydrophobic The rule of monomer-polymer does not ideally apply to them (fatty acids – monomers)  Biological Functions of Lipids Storag...

Lipids  Lipids: Structurally Diverse Class Organic molecules that are characterized by low solubility in water => relatively hydrophobic The rule of monomer-polymer does not ideally apply to them (fatty acids – monomers)  Biological Functions of Lipids Storage of energy – Reduced compounds: lots of available energy – Hydrophobic nature: good packing Insulation from environment – Low thermal conductivity – High heat capacity (can “absorb” heat) – Mechanical protection (can absorb shocks) Water repellant – Hydrophobic nature: keeps surface of the organism dry Prevents excessive wetting (birds) Prevents loss of water via evaporation  More Functions Membrane structure – Main structure of cell membranes Cofactors for enzymes – Vitamin K: blood clot formation – Coenzyme Q: ATP synthesis in mitochondria Signaling molecules – Paracrine hormones (act locally) – Steroid hormones (act body-wide) – Growth factors – Vitamins A and D (hormone precursors) Pigments – Color of tomatoes, carrots, pumpkins, some birds Antioxidants – Vitamin E Fatty Acids Fatty Acids Saturated Fatty Acids Unsaturated Fatty Acids Fatty Acid Naming Systems  Essential fatty acids Fatty acids that cannot be synthesized de novo in sufficient quantities for normal physiological function. Mammals lack the ability to introduce double bonds in fatty acids beyond carbon 9 (∆9): Linoleic acid (Omega 6) – 18:2 Linolenic acid (Omega 3) – 18:3  Lipids classification Simple non-polar lipids fats/oils = triglycerols Complex amphiphatic lipids phospholipids, sphingolipids, glycolipids Complex almost non-polar lipids sterols  Major Types of Lipids Almost non-polar Cholesterol Fatty acid + Cyclic hydrocarbons Triglycerols = triglycerides Glycerophospholipids = phosphoglycerides  Fatty Acids Glycerol Backbone Ester Bonds Fat or Oil Structure Triacylglycerol  Energy storage in average individual Triglycerides Protein Glycogen Glucose 420 000 kJ 100 000 kJ 2 500 kJ 170 kJ Whereas carbohydrate storages are used up after a day, fat storage can help sustain our energy needs for several weeks. In humans, triglycerides are stored in specialized cells called adipose cells (adipocytes). Within these cells, triglycerides aggregate in the cytoplasm to form a large fat globule that makes up the majority of the volume of the cell Oils (plant triglycerides) => contain cis-unsaturated fatty acids, poorly packed => low melting temperature due to weaker intermolecular interactions (input less energy to break these bonds) => fluid => “good” fats Fats (animal triglycerides)=> contain saturated fatty acids, tightly packed => high melting temperature due to stronger intermolecular interactions => solid => “bad” fats Artificial fats (butter) => contain trans-unsaturated fatty acids, tightly packed => high melting temperature due to stronger intermolecular interactions => “less fluid/solid-ish” => “bad” fats Saturated and Unsaturated Fats in Food Lipids  Trans Fatty Acids Trans fatty acids form by partial hydrogenation of unsaturated fatty acids – Done to increase shelf life or stability at high temperature of oils used in cooking (especially deep frying) A trans double bond allows a given fatty acid to adopt an extended conformation Trans fatty acids can pack more regularly and show higher melting points than cis forms Consuming trans fats increases risk of cardiovascular disease  Major Types of Lipids Almost non-polar Cholesterol Fatty acid + Cyclic hydrocarbons Triglycerols = triglycerides Glycerophospholipids = phosphoglycerides  Membrane lipids - phospholipids Most phospholipids contain: 1. A platform molecule (glycerol for phosphoglycerides, sphingosine for sphingolipids) 2. One or more fatty acids (one for sphingolipids, more than one for phosphoglycerides) 3. A phosphate group 4. An alcohol component Phospholipids are amphipathic Phosphatidylcholine  Phosphatidylcholine Phosphatidylcholine is the major component of most eukaryotic cell membranes Many prokaryotes, including E. coli, cannot synthesize this lipid; their membranes do not contain phosphatidylcholine  Membrane lipids - glycolipids Glycolipids are carbohydrates containing lipid molecules with sphingosine or glycerol as a platform molecule (a backbone) The galactolipids are predominate in plant cells: localized in the thylakoid membranes of chloroplasts; they make up 70% to 80% of the total membrane lipids of a vascular plant Sphingolipids Sterols => lipids with common ring structure Progenitor => cholesterol (stigmasterol in plants) Functions of cholesterol: -In the membranes -Signaling molecule Cholesterol derivatives: -Steroid hormones -Vitamin D Cholesterol – Steroid (= 4 fused rings) Cholesterol in the Lipid Bilayer  Steroid Hormones Made from Cholesterol Multistep Glucose Metabolism Salt Excretion Cholesterol Anti-inflammatory  Synthesis of Vitamin-D Regulate Calcium Metabolism Isoprene Vitamins Mitochondrial and Chloroplast Membrane Electron Carriers