Lipids1.pdf

Introduction to Cell Biology & Biochemistry Dr Alessandro Siani  Types of Biomolecules Nucleic acids (nucleotides) Proteins (amino acids) Carbohydrates (sugars)...

Introduction to Cell Biology & Biochemistry Dr Alessandro Siani  Types of Biomolecules Nucleic acids (nucleotides) Proteins (amino acids) Carbohydrates (sugars) Lipids Dr Alessandro Siani  Lecture overview: Introduction to lipids Structure and properties of fatty acids Classification of lipids Dr Alessandro Siani  What are lipids? Lipids are a very broad class of molecules that are insoluble in water (e.g. waxes, oils, fats etc.) Dr Alessandro Siani  What do lipids do? Energy storage Biomembranes Signaling Enzymatic co-factors Dr Alessandro Siani … and more!  By definition lipids are either: HYDROPHOBIC Fully water hating/insoluble in water Or Dr Alessandro Siani AMPHIPATHIC Water soluble and water insoluble groups on one molecule  Lipids can be classified as: Those derived from fatty acids e.g. phospholipids, triglycerides Those derived from sterol Dr Alessandro Siani e.g. oestrogen, cholesterol  Fatty Acids Hydrophilic “head” Hydrophobic “tail” (mostly 12 to 24 carbons, even number only) Dr Alessandro Siani Dr Alessandro Siani Fatty Acids can be subdivided in: Dr Alessandro Siani Mono- and poly-unsaturation  Structural isomerism in fatty acids Rotation about the C=C double bond is not allowed. So, unsaturated fatty acids can have two configurations Dr Alessandro Siani Cis double bonds cause kinks in the chain. Can you explain why?  Structural isomerism in fatty acids Rotation about the C=C double bond is not allowed. So, unsaturated fatty acids can have two configurations Dr Alessandro Siani  Fatty acids nomenclature (standard) Hexadecenoic acid Count the carbons starting from COOH Write that number down followed by a colon 16: Count the double bonds Write that number down after the colon 16:1 Count the first carbon of the double bond Write that number as a superscript to a delta (D) 16:1D9 For unsaturated fatty acids, write down Dr Alessandro Siani the cis/trans configuration. Cis, 16:1D9 hexadecenoic acid (better known as palmitoleic acid) Cis double bonds cause kinks in the tail Dr Alessandro Siani Fatty acids nomenclature (omega)  Melting points The longer the chain the higher the melting point. WHY? Cis configuration double bonds lower the melting point. WHY? Dr Alessandro Siani Dr Alessandro Siani Melting points – real life examples Dr Alessandro Siani Classification of lipids *recent footage of Dr Siani trying to figure out an easy way to explain lipids’ classification. Dr Alessandro Siani Classification of lipids  Classification of lipids By synthetic pathway (e.g. steroids vs fatty acids) By function (e.g. source of energy, membrane components, messengers…) By structure (e.g. simple, complex, derived) By chemical composition (e.g. phospholipids, glycolipids) Dr Alessandro Siani Lipids may fall in different groups depending on which criteria we use to classify them. To further complicate things, there are frequent overlaps between categories.  Glycerolipids Composed of glycerol and fatty acids Glycerol Glycerol is a 3-Carbon polyalcohol Triglycerides are a typical class of glycerolipids… Dr Alessandro Siani However they are NOT the only type!  Glycerol A triglyceride + Esterification Dr Alessandro Siani + 3 H20 3 Fatty acids (in this case, three different ones)  Roles of triglycerides Energy storage: Energy rich (more than sugars!) ‘Pack up’easily Buoyancy: Low density Density changes with temperature Dr Alessandro Siani Thermal insulation Fats do not conduce heat well, so they prevent heat loss.  Phosphoglycerides Sometimes called GLYCEROPHOSPHOLIPIDS Important in biomembranes Are a class of PHOSPHOLIPIDS Glycerol+Fatty acids+Phosphate group+polar head Dr Alessandro Siani Dr Alessandro Siani  Galactolipids NOT phospholipids Galactose linked by a glycosidic bond to glycerol The fatty acids are linoleic acid Dr Alessandro Siani  Sphingolipids Based on Sphingosine Can be phospholipids Can be simple or complex Dr Alessandro Siani Dr Alessandro Siani  Why do you think storage lipids are neutral while membrane lipids are polar? Dr Alessandro Siani (this is a difficult question at this point, so do not worry if you can’t think of an answer)  Waxes Long chain alcohols + fatty acids Higher melting points than triglycerides Some marine creatures use them for energy storage Have water-proofing qualities Dr Alessandro Siani