The Plasma Membrane Section 7.2 p.175-178

Maintaining a Balance All living cells must maintain a balance regardless of internal + external conditions Survival depends on the cell’s ability to maintain proper conditions within itself

Why cells must control materials Cells need nutrients to function Glucose Amino acids Lipids Must enter through the plasma membrane The flexible boundary between the cell + its environment

Why cells must control materials Substances such as wastes + products must leave through the plasma membrane Substances enter + leave to maintain homeostasis Selectively permeable Ability to allow some molecule to pass through while keeping others out Examples Water vs. Na+ ions

Selectively Permeable

Structure of the Plasma Membrane Recall – LIPIDS (Fatty Acids + glycerol) Phospholipid Two fatty acids, glycerol, + a phosphate group Plasma membrane is composed of a phospholipid bilayer

The Phospholipid bilayer Fatty acids “tails” are hydrophobic Don’t want to interact with water Phosphate group “head” is hydrophilic Wants to interact with water Creates a barrier that regulates the ease in which substances cross the plasma membrane

Fluid Mosaic Model The proteins embedded in the bilayer create the “mosaic” The phospholipids move within the membrane (like a fluid)

Other components of the P.M. Cholesterol Helps to stabilize the phospholipids by preventing their FA’s from sticking together

Other components of the P.M. Proteins Transport Move substances through PM Markers Identify chemical signals + each other Inner surface Gives cell’s structure flexibility

A video clip…. Plasma Membrane