1. Cell Membrane

2. Cellular membranes are fluid mosaics of lipids and proteins Phospholipids are the most abundant lipid in the plasma membrane (fluid portion of the membrane) The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. The plasma membrane is a bilayerof phospholipids that form a fluid matrix in which various proteins (blue) are embedded. Many proteins have carbohydrates attached to them, forming glycoproteins. Three of the five major types of membrane proteins are illustrated here: recognition, receptor, and transport proteins.

4. Phospholipid

5. Head is a phosphate bonded to a glycerol

6. Tails are fatty acids (chains of hydrogen and carbon atoms, termed “hydrocarbon chain”)

7. Hydrocarbon tail (fatty acids) can be saturated or unsaturated Saturated Have as many hydrogen present as can bond to the carbons (so they lack double bonds between the carbons) Causes a straight chain (which decreases fluidity of the membrane)

8. Unsaturated Have fewer hydrogen present then can bond to the carbons (so there are double bonds between the carbons) Causes kinked chains (which increases fluidity in the membrane because kinks at the carbon-to- carbon double bond hinder close packing of phospholipids.)

11. The cell exterior and interior face watery environments

12. Hydrophilic(“water loving”) head portions are exposed to water. Hydrophobic(“water fearing”) tail portions of are oriented inside the bilayer. Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions

14. Why called “FLUID” Phospholipid bilayer is flexible, allowing for cellular shape changes Membrane lipids (and some proteins) can drift laterally within the membrane. Individual phospholipid molecules are not bonded to one another Proteins drift more slowly than lipids Some membrane proteins are tethered to the cytoskeleton and cannot move far.

15. Lateral movement (  10 7 times per second) Flip-flop (  once per month)

16. Membranes must be fluid to work properly!!!!!

18. In eukaryotes, a fat molecule called cholesterol modulates the membrane fluidity by making the membrane: –Less fluid at warmer temperatures –More fluid at lower temperatures Cholesterol affects in membrane

19. Membrane proteins form a “Mosaic” Proteins determine most of the membrane’s specific functions Peripheral proteins are bound to the surface of the membrane Integral proteins penetrate the hydrophobic core

21. 5 major functions of membrane proteins: Receptor Proteins Recognition Proteins Enzymatic Proteins Adhesion Proteins Transport Proteins

22. RECEPTOR PROTEINS Receptor proteins bind to specific molecules found outside the cell (like hormones) and trigger changes in cell action

23. RECOGNITION PROTEINS Serve as identification tags on the surface of a cell Membrane carbohydrates may be covalently bonded to lipids (forming glycolipids) or more commonly to proteins (forming glycoproteins)

24. ENZYMES Promote chemical reactions that synthesize or break apart biological molecules Speed up reactions

25. ADHESION PROTEINS Anchor the cell membrane to inner cytoskeleton, to proteins outside the cell, and to other cells

26. TRANSPORT PROTEINS Allow substances to move into or out of the cell through the membrane –Channel proteins serve as pores through which substances can move –Carrier proteins bind specific substances and change shape to force the material across the membrane

28. (a) Transport (d) Cell-cell recognition (b) Enzymatic activity (e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM) (c) Recepetor