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Section 7.1 Fluid Mosaic Cell Membrane
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Table of Contents The Basics Models of Membranes The Fluidity of Membranes Membrane Proteins and Their Functions 6 Major Functions Of Proteins in Plasma Membrane Role of Membrane Carbs in Cell-Cell Recognition Synthesis and Sidedness of Membranes
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The Basics Plasma membrane controls the traffic of molecules into out of the cell Selective permeability allows some substances across the membrane more easily than others Lipids and proteins are the staples of membranes Phospholipids are amphipathic molecules and have an inherent ability to form membrane Amphipathic – meaning both hydrophobic and hydrophilic regions The FLUID MOSAIC MODEL Membrane is a fluid structure Proteins are embedded or attached to double layer of the membrane
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Models of Membranes 1915 - E. Gorter & F. Grendel – Phospholipid bilayer 1935 – H. Davson & J. Danielli – Sandwich Model 1960’s widely accepted Late 1960’s – Sandwich Model Challenged Membranes no longer considered identical The proteins were placed wrong 1972 – S. J. Singer & G. Nicolson – Proteins dispersed Freeze-facture test
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Freeze Fracture
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The Fluidity of Membranes Movement Phospholipids move rapidly about 10 7 times per second Proteins drift slowly Membrane remains fluid as temp. decreases until it becomes a tightly packed arrangement Membranes rich in phospholipids can more easily remain fluid if they contain unsaturated hydrocarbons -kinks from double bonds prevent tight packing Cholesterol in animal cells will act as a temperature buffer and resist changes in membrane fluidity -hinders movement and close packing of phospholipids Membranes have to be fluid to work properly
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Membrane Proteins and Their Functions More than 50 types of proteins which can determine membrane’s specific functions Integral Proteins Penetrate the hydrophobic core of the membrane Many span both layers and are called transmembrane proteins Peripheral Proteins Not embedded in lipid bilayer Attached loosely to surface as appendages Some membranes are attached to cytoskeleton Protein attachment builds stronger framework
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6 Major Functions Of Proteins in Plasma Membrane Transport – facilitated molecules, ATP hydrolyisis Enzymatic Activity – metabolic machinery Signal Transduction - chemical messengers Cell-Cell Recognition – identification tags or targets Intercellular Joining Attachment to the cytoskeleton and extracellular matrix - maintains cell shape & stabilizes protein location
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The Role of Membrane Carbs in Cell-Cell Recognition Cell-Cell Recognition - a cell’s ability to distinguish one type of neighboring cell from another Glycolipids – carbs that are covalently bonded to lipids Glycoproteins – carbs that bond covalently to proteins The differences of the carb molecules and the placement on the membrane act as markers to other cell
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Synthesis and Sidedness of Membranes Membranes have distinct inside and outside faces Synthesis Process – Endomembrane system Synthesis of membrane proteins and lipids begin in ER and carbs and proteins and combined to form glycoproteins In the Golgi Apparatus, glycoproteins are modified and glycolipids are formed Transmembrane proteins, membrane glycolipids, and secretory proteins are transported to the plasma membrane Vesicles fuse with membrane, releasing secretory proteins from cell
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Review *________ acts a “temperature buffer” by preventing a change in fluidity due to temperature changes.
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Review The _________portion of the model is the assortment of all types of proteins attached or inside the cell membrane. Proteins may be ___________________which reside in both the hydrophilic and hydrophobic regions of the cell membrane or peripheral proteins that bind to the ________ (hydrophilic portion) of the cell membrane. Other structures on the surface of a cell membrane are glycolipids and ___________ Glycolipids are _________attached to ______, and glycoproteins are sugars covalently bonded to proteins. Proteins serve many purposes in the cell membrane: enzymatic activity, signal transduction, intercellular joining, attachment to the cytoskeleton and extracellular matrix, ___________ (glycoproteins and glycolipids), and ___________.
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