Cell Membranes

role of membranes in cells

• transports raw materials into the cell (nutrients, ions, gases etc.)

• transports toxic or foreign products and waste out

• prevents entry of unwanted matter

• prevents escape of functional matter

fluid mosaic model

the cell membrane has a phospholipid bilayer, very fluid

components are free to float and move around, bumping into each other when moving laterally from side to side

phospholipid bilayer

double layer of phospholipids

head = hydrophilic, tail = hydrophobic

tails face inward (away from the aq environment), heads face outward

cholesterol (type of lipid) function in an animal cell membrane

high temp - helps maintain firmness in the oily membrane bilayer, prevents too much flexibility that will weaken the membrane

low temp - keeps membrane fluid, flexible and function from freezing

makes the membrane less permeable to molecules by packing themselves between phospholipids tails in the bilayer

types of protein in the cell membrane

peripheral and integral proteins

peripheral protein function in an animal cell membrane

• found on the internal and external surface of the cell’s membrane

• do not contact with hydrophobic regions, it is near aqueous environment on the surfaces

• securely attached to the cytoskeleton, maintain position for efficient function

integral protein function in an animal cell membrane

• found throughout the entire bilayer

• function as channels or pumps, passively or actively moving molecules

• acts as receptors on the surface by binding to specific molecules outside the cell, able to sense and respond to external changes for homeostasis

function of glycoproteins

• they are integral membrane proteins with carbohydrate chains attached externally

• carbohydrate chains will attach so cells can recognize each other and communicate, adhere to one another to form tissues

• immune responses to identify bacteria/viruses and will form a “sugar coating” on the cell surface as a barrier to protect

glycolipids function

carbohydrate chains attached to phospholipids

carbohydrate chains serves as receptors by binding to external molecules, triggering a cellular response to maintain homeostasis

stabilize the membrane