Chapter 5: Structure and Function of Plasma Membrane

5.1 Components of cell membrane

Fluid Mosaic Model The plasma membrane separates a cell’s external environment Regulates substances into and out of cells Communicates with other cells Fluid mosaic model: cell’s membrane is a fluid of mixed composition Molecules are embedded within lipid bilayer (proteins, cholesterol)

Membrane Proteins Recognition proteins: identifies “self” cells Receptor proteins: triggers a change in cell activity Transport proteins: assists the movement of molecules across the membrane

5.2 Passive transport

Diffusion Molecules tend to spread apart towards low concentrations Semipermeable membranes allow some materials oxygen, carbon dioxide and lipids pass through Other molecules (sugars and ions) require specific transport proteins As molecules move across the overall concentration will reach equilibrium Diffusion across a membrane is passive because it requires no work Diffusion across a membrane is passive because it requires no work

5.3 Active Transport

Against the grain If a cell needs maintain a high concentration work must be done Active Transport requires proteins that act as a pump molecules against the concentration gradient Example is the Na/K pump

5.4 Bulk Transport

Exocytosis – vesicles fuse with outer membrane and release materials Endocytosis – vesicles form in outer membrane trapping materials outside the cell Phagocytosis – cell “eating” Pinocytosis – cell “drinking”