The document summarizes key aspects of cell membranes. It notes that membranes form specialized compartments through selective permeability, creating concentration gradients and differences in pH and charge. Membranes contain proteins and lipids that give membranes structure and allow for functions like selective transport and cell signaling. The lipid bilayer is composed of phospholipids with hydrophobic tails inside and hydrophilic heads outside, and integral and peripheral proteins embed within or attach to the surface of the bilayer.

1. OPTOM FASLU MUHAMMED

5.  Membrane Functions
 Form specialized compartments by selective permeability
 Unique environment
 Creation of concentration gradients
 pH and charge (electrical, ionic) differences
 Asymmetric protein distribution
 Cell-Cell recognition
 Site for receptor molecule biding for cell signaling
 Receptor binds ligand (such as a hormone)
 Induces intracellular reactions
 Controls and regulates reaction sequences
 Product of one enzyme is the substrate for the next enzyme
 Can "line up" the enzymes in the proper sequence

6.  Lipid bilayer composed of phospholipids
Hydrophobic tails inside
 Hydrophilic heads outside
 This forms two separate water-interacting surfaces
 Proteins coat outer surface
 This forms a protein-lipid sandwich
 Proteins do not permeate the lipid bilayer

7.  Membrane Lipids
 Phospholipids most abundant
 Phosphate may have additional polar groups such as choline,
ethanolamine, serine, inositol
 These increase hydrophilicity
 Cholesterol - a steroid
 Can comprise up to 50% of animal plasma membrane
 Hydrophilic OH groups toward surface
 Smaller than a phospholipid and less amphipathic (having
both polar and non-polar regions of the molecule)
 Reduces membrane fluidity by reducing phospholipid
movement
 Other molecules include ceramides and sphingolipds - amino
alcohols with fatty acid chains
 These lipids distributed asymmetrically

8.  Fluidity depends on lipid composition
 Membrane Carbohydrates
 Face away from cytoplasm (on outside of cell)
 Attached to protein or lipid
 Blood antigens - Determine blood type - bound to lipids
(glycolipids)
 Glycoproteins - Protein Receptors
 Provide specificity for cell-cell or cell-protein
interactions

9.  Membrane Proteins
 Peripheral Proteins
 completely on membrane surface
 ionic and H-bond interactions with hydrophilic lipid and
protein groups
 Integral Proteins
 Possess hydrophobic domains which are anchored to
hydrophobic lipids
 alpha helix
 more complex structure