Chapter 6 Lipids How is the cell membrane dependent on lipids Lipids Generic term for carbon compounds found in organisms that are largely Unlike amino acids nucleotides and monosaccharides lipids are characterized by a physical instead of shared chemical structure Made up of hydrocarbons and fatty acids Hydrocarbons Contain only carbon and hydrogen Fatty Acids Hydrocarbon bonded to a COOH Three Types of Lipids Found in Cells Lipid structure varies widely The three most important types of lipids found in cells 1 are composed of three fatty acids linked to glycerol Also called triacylglycerols or triglycerides Store Energy Three Types of Lipids Found in Cells The three most important types of lipids found in cells 2 are a family of lipids with a distinctive fourring structure Cholesterol is an important steroid in mammals Precursors to hormones Components of cell membranes Three Types of Lipids Found in Cells The three most important types of lipids found in cells 3 consist of a glycerol linked to a phosphate group PO42 and to either two chains of isoprene or two fatty acids Amphipathic Main component of cell membranes Phospholipids and Water Phospholipids do not dissolve when they are placed in water but are meaning they contain both hydrophobic and hydrophilic elements Water molecules interact with the hydrophilic heads but not with the hydrophobic tails This Upon contact with water phospholipids form either Micelles Heads face the water and tails face each other Phospholipid bilayers lipid bilayers The Importance of Membranes The plasma membrane or cell membrane separates life from nonlife The plasma membrane separates the cell s interior from the external environment Membranes function to Bond Saturation is an Important Aspect of Lipid Structure The fluidity of lipids depends on the length and saturation of their hydrocarbon chains Selective Permeability of Lipid Bilayers The permeability of a structure is its tendency to allow a given substance to pass across it Phospholipid bilayers have Small or nonpolar molecules move across phospholipid bilayers Charged or large polar substances cross if at all Why Do Molecules Move Across Lipid Bilayers Molecules and ions move randomly in all directions when a concentration gradient exists but their net movement in from regions of high concentration to low concentration This process is spontaneous because it results in an increase in entropy is established once the molecules or ions are randomly distributed throughout a solution Why Do Molecules Move Across Lipid Bilayers Like other substances that diffuse water moves along its concentration gradient The movement of water across the selectively permeable membrane is called How Do Biologists Study the Components of the Plasma Membrane The Cell Membrane The of membrane structure suggests that some proteins are inserted into the lipid bilayer making the membrane a fluid dynamic mosaic of phospholipids and proteins Overview of Membrane Transport is when molecules and ions move from high concentration regions to low concentration regions It increases entropy and is thus spontaneous by transporters occurs only down a concentration gradient reducing differences between solutions move s materials against their concentration gradient and requires energy provided by ATP or an electrochemical gradient Key Concepts Plasma membranes are made up of selectively permeable bilayers of phospholipids Phospholipids are amphipathic lipid molecules they have hydrophobic and hydrophilic regions Ions and molecules diffuse spontaneously from regions of higher concentration to regions of lower concentration Movement of water across a plasma membrane is called osmosis In cells membrane proteins are responsible for the passage of insoluble substances that can t cross the membrane on their own
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