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BU BIOL 118 - Lipids

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Bio 118 1st Edition Lecture 5 Outline of Last Lecture I. Protein Structure and Functiona. The Nature of Side chainsb. Important Terminologyc. Functional Groups Affect Reactivityd. Primary Structuree. Secondary Structure f. Tertiary Structureg. R-group Interactions That Form Tertiary Structuresh. Summary of Protein Structurei. Protein Function: What Do Proteins Do?j. Folding and Functionk. Protein Folding Is Often Regulatedl. Prions and Protein FoldingII. Nucleic Acids and the RNA Worlda. Summary of DNA’s Secondary Structureb. How Does DNA Replicate?c. Is DNA a Catalytic Molecule?d. RNA Structure and Functione. Glycosidic Linkagesf. Types of PolysaccharidesOutline of Current Lecture a. Lipids: What is a Lipid?b. The Importance of Cell Membranesc. Three Types of Lipids Found in Cellsd. Fats & Oils (Triglycerides)e. Sterolsf. Phospholipidsg. Phospholipids & Waterh. Phospholipid Bilayersi. Selective Permeability of Lipid Bilayersj. Many Factors Affect Membrane Permeabilityk. Bond Saturation and Membrane PermeabilityCurrent LectureThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Lipids: What is a Lipid?- Lipids: carbon-containing compounds that are found in organisms and are largely nonpolar & hydrophobic- Unlike carbs, proteins & nucleic acids, they are defined based on their solubility properties o Not by their shared chemical structure- Hydrocarbons: most commonly known nonpolar lipid molecules that contain only carbon and hydrogen- Lipids do not dissolve in water because most have a hydrocarbon chain bonded to a carboxyl (-COOH) group- Fatty acids and isoprene are the key building blocks of lipidsThe Importance of Cell Membranes - Plasma Membrane (cell membrane): separates life from nonlife. Made of phospholipid- The plasma membrane separates the cell’s interior from the external environment- Function of membranes:o Keep damaging materials out of the cello Allow entry of materials needed by the cello Facilitate the chemical reactions necessary for lifeThree Types of Lipids Found in Cells- Fats & Oils (triacylglycerols/triglycerides)o Composed of 3 fatty acids linked to glycerol backbone- Sterolso Family of lipids with distinctive four-ring structureo Cholesterol is an important sterol in mammalso Serves as precursor to important biological molecules, including steroid hormones, sex hormones & vitamin D- Phospholipidso Consist of glycerol backbone linked to a phosphate group and to either 2 chains of isoprene or 2 fatty acids. o Structure similar to triglyceridesFats & Oils- Triglycerides, otherwise known as fats (solid at room temperature) and oils (liquid at room temperature) are comprised of non-polar molecules made up of 3 fatty acids linked to a glycerol (3 carbon) backboneo Most abundant of lipids found in food & bodyo Saturated, mono-unsaturated, polyunsaturated and trans-fats are distinguished from each other based on degree of saturation and the location of the hydrogens Trans-fats have hydrogen opposing one another at point of unsaturation, resulting in a linear molecule that mimics saturated fatso Also distinguished by long chain (12 carbons or longer), medium chain (6-10 carbons), short chain (less than 6 carbons) fatty acidso Fats form due to dehydration reactionso Glycerol is soluble in water due to –OH groups o Triglycerides= glycerol + 3 fatty acids (attached to carbon by ester linkages) Fatty acids= Double O bond at the topSterols- Family of lipids distinguished by bulky, four-ring structure- Differ from one another by the functional groups or side groups attached to different carbons in those hydrophobic rings- Structure:o Hydrophilic hydroxyl group attached to the top ring and an isoprenoid “tail” attached at the bottom - Cholesterol o An important component of plasma membranes in many organisms o Maintains the fluidity if the cell membrane by regulating the integrity of the cell membrane & keeps the cell membrane from becoming too lose or stiffPhospholipids- Similar to triglycerides: glycerol backbone, 2 fatty acids BUTTT instead of 3rd fatty acid has a phosphorous group that has a charge (polar)- Membrane-forming lipids contain both a polar, hydrophilic region and a nonpolar, hydrophobic region- Phospholipids are amphipathic:o The head region: glycerol, phosphate & charged group. Highly polar covalent bondso The tail region: 2 nonpolar fatty acid or isoprene chains- When placed in solution, the phospholipid heads interact with water while the tails do not, allowing these lipids to form membranesPhospholipids and Water- Phospholipids do not dissolve when they are placed in water- Water molecules interact with the hydrophilic heads but not with the hydrophobic tailso Drives hydrophobic tails together- Upon contact with water phospholipids form either:o Micelles Heads face the water and tails face each othero Phospholipid Bilayers (lipid bilayers) Hydrophobic tails are attracted to one another Very fluidPhospholipid Bilayers- Form when 2 sheets of phospholipid molecules align. The hydrophilic heads in each layerface a surrounding solution, while the hydrophobic tails face one another inside the bilayer- Form spontaneously, with no outside input of energy requiredSelective Permeability of Lipid Bilayers- The permeability of a structure is its tendency to allow a given substance to pass across it- Have selective permeabilityo Small or nonpolar molecules move across phospholipid bilayers quicklyo Charged or large polar substances cross slowly, if at allMany Factors Affect Membrane Permeability- Many factors influence the behavior of the membrane:o Number of double bonds between the carbons in the phospholipid’s hydrophobictailo Length of the tailo Number of cholesterol molecules in the membraneo TemperatureBond Saturation & Membrane Permeability- Double bonds between carbons in a hydrocarbon chain can cause a “kink” in the hydrocarbon chain, preventing the close packing of hydrocarbon tails and reducing hydrophobic interactionso Unsaturated hydrocarbons have at least one double bondo Called unsaturated because one or more points along hydrocarbon chain where hydrogen is absent; thus creating the point of saturationo At this point, there will be a double bond between C atomso Hydrocarbon chains without double bonds are termed saturated (saturated referring to how every C is bonded to as many hydrogen as possible; hence no


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