Cell Membrane

Cell Membrane? Location?  Surrounding the cell Function? 1.Protection and support for the cell 2.Regulation of what enters and exits the cell WHY? -Essential in order to maintain *homeostasis within the cell *maintaining normal internal conditions

Composition of Cell Membrane  Phospholipid Bilayer 1.Phospholipid:  Hydrophilic Head; “water-loving”  Hydrophobic Tail; “water-fearing” 2.Bilayer  Two-layers (of phospholipids)

Composition of Cell Membrane  Proteins embedded throughout phospholipid bilayer  Integral Proteins: Span the width of the cell membrane  Peripheral Proteins: Located on one side of the cell membrane (or on the ‘periphery’)  A variety of different types of proteins within the cell membrane, each with different functions

Composition  Cholesterol: another lipid that maintains the structural stability of the cell membrane  Carbohydrates: allow for cell-to- cell recognition; a “fingerprint” for each cell  Allows for the immune system to recognize ‘foreign’ cells and attack them  Attached to proteins or phospholipids on outside layer of cell membrane

 Break it down:  FLUID: The cell membrane is constantly moving due to the lipid “tails” on its interior; they “wiggle”  This means that the cell membrane is pliable  The cell membrane has the consistency of olive oil at body temp.  MOSAIC: Proteins of different types, randomly positioned throughout the membrane create a “mosaic” appearance The cell membrane is a constantly moving assemblage of parts. Fluid Mosaic Model

 Transport of molecules from one side of the membrane to the other in order to maintain homeostasis within the cell.  Selectively Permeable: Only certain substances can move across the membrane while others cannot.  Small, non-charged molecules (H20, CO2, O2, etc.) can freely cross the cell membrane.  This is referred to as Passive Transport: molecules are ‘freely’ or ‘passively’ traveling through the cell membrane  This occurs through one of two ways: Diffusion or facilitated diffusion Cell Membrane Function

Passive Transport: Diffusion  No Energy is required  Diffusion: the movement of molecules from a higher concentration to a lower concentration until equilibrium is reached  Concentration: the amount of solute in the solvent  Solute: dissolved substance (in the solvent)  solvent: the liquid containing the dissolved substance  Equilibrium: occurs when the solute concentration is the same throughout the system; equal on both sides of the membrane

 A form of Passive Transport (so no energy required)  Facilitated Diffusion: Larger molecules (that are unable to passively cross the cell membrane) are “carried” through via a channel protein.  Specific protein channels carry specific types of molecules  For example: glucose is transported across the cell membrane via facilitated diffusion Passive Transport: Facilitated Diffusion