2.4 Plasma Membranes

Clle have membranes that allow them to establish and maintain internal environments that are different from their external environments. Describe the roles of each of the components of the cell membrane in maintaining the internal environment of the cell. Phospholipids have both hydrophilic and hydrophobic regions. The hydrophilic phosphate regions of the phospholipids are oriented toward the aqueous external or internal environments, while the hydrophobic fatty acid regions face each other within the interior of the membrane. Embedded proteins can be hydrophilic, with charged and polar side groups, or hydrophobic, with nonpolar side groups. Describe the Fluid Mosaic Model of cell membranes. Cell membranes consist of a structural framework of phospholipid molecules that is embedded wtih proteins, steroids (such as cholesterol in eukaryotes), glycoproteins, and glycolipids that can flow around the surface of the cell within the membrane.

plasma membrane

semi-permeable membrane that controls substance movement and encloses that cytoplasm

• comprised of phospholipids which form a bilayer

• hydrophobic fatty acid tails face inwards/each other in interior of the membrane

• hydrophilic phosphate head is turned outwards towards aqueous environments

fluid mosaic model

cell membranes consist of a structural framework of phospholipid molecules that is embedded with proteins, steroids (such as cholesterol in eukaryotes), glycoproteins, and glycolipids that can flow around the surface of the cell within the membrane

• functions: adhesion (junctions), reception, transport.channels

proteins in the membrane

• embedded/integral proteins

  • transmembrane proteins - parts both inside and outside of the cell

  • hydrophilic - charged and polar side groups

  • hydrophobic - nonpolar side groups

• peripheral proteins - binded to surface of cell membrane

cholesterol in the membrane

stabilize membrane fluidity in animal cells

glycolipids/glycoproteins

carbohydrate side chains binded to lipids/proteins

• markers for cell-cell recognition, found on extracellular side