Cell membrane

Membrane 

• Outer layer of cell 
• Seperates intracellular substances from ectracellular substances 
• Encloses and supports cell contents 
• Attaches cell to extracellular enviroment or other cells 
• Cell's ability to recognize and communicate with each other takes place through plasma membrane
• Determines what moves in and out of cell
• Intracellular conents of cells are diffrent from extracellular environments 
• Electrical charge diffrences across the plasma membrane called the membrane potential (result of cells regulations of ion movement into and out of the cell)
• More positively charged ions on the outside of the plasma membrane and more negitavily charged ions and proteins inside, plasma membrane is positively charged 
• Lipids = 45-50% of weight of plasma
• Proteins = 45-50% of the weight 
• Carbonhydrates make up a small percentage of plasma membrane 
• Found only on the outer surface of the plasma membrane 
• Carbonhydrates combine with lipids to form glycolipids and with proteins to form glycoproteins 
• Glycocalyx collection of glycolipids, glycoproteins and carbonhydrates on the outer surface of plasma membrane 
• Glycocalyx contains molecules absorbed from the extracellular environment 
• No precise oundary between the plasma membrane and the extracellular environment 

Lipids 

• Two predominant lipids of the plasma membrane are phospholipds and cholestrol 
• Phospholipds assemble to form a lipid bilayer, a double layer of phospholipid molecule (polar head and a nonpolar tail 
• Polar head is attached to water (hydrophilic) exposed to aqueous extracellular and intracellular fluids of cell 
• Tails of the phospholipds are non polar and are not attracted to water molecules, tails are called hydrophobic 
• Nonpolar, hydrophobic tails face one another in the inferior plasma membrane 
• Plasma membrane is highly flexible and can change shape and composition 
• Lipid bilayer functions as a dense liquid in which other moelcules, such as proteins are suspended. 
• FProvides an important means of distributing molecules within the plasma membrane 
• Slight damage to the membrane can be repaired because the phospjolipds tend to reassemble around damaged sites and close them
• Fluid nature of lipid bilayer also enables membranes to fuse with eachother 
• Cholestrole is a lipid 
• Interspersed among the phospholipids and accounts for one third of the total lipids in plasma membrane 
• Hydrophilic hydroxyl group of cholestrol extends between the phospholipd heaads to the hydrophilic surface of the membrane 
• Amount of cholestrole found is a major factor in determing the fluid nature of the membrane 
• Cholestrol, is that it limits the movement of phospholipids, provides stability to plasma membrane 

Membrane proteins 

• Integral membrane proteins penetrate deeply into the lipid bilayer
• Peripheral membrane proteins are attached to either the inner or outer surface of the lipid bilayer
• Intergral membrane protein consists of regions made up of amino acids with hydrophobic R groups
• Membrane proteins function as marker molecules, attachment proteins, transport proteins, receptor proteins and enzymes. 

marker molecules 

• Allow cells to identify other cells or molecules (glyocoproteins)

Attachment proteins 

• Integral proteins that allow cells to attach tio other cells or to extracellular molecules 
• Cadherins are proteins that attach to other cells 
• Integrins are proteins that attach to extracellular molecules 

Transport proteins 

• Intergral proteins that allow ions…