1. Section 7.1 Fluid Mosaic Cell Membrane

2. 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

3. 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

4. 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

5. Freeze Fracture

6. 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

8. 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

10. 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

11. 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

12. 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

13. Review *________ acts a “temperature buffer” by preventing a change in fluidity due to temperature changes.

14. 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 ___________.