Functions Protects the cell Semi-permeable barrier: selects incoming and outgoing substances (passive/active transport) Maintain concentration of various substances Allows cell recognition/communication Allows receptivity (hormones, etc) Allows the cell to maintain its shape Helps compartmentalize subcellular domains Phospholipids are a major component of cell membranes.
Fluid Mosaic Model (1972) - Phospholipid bilayer with proteins forming a mosaic pattern as they float/penetrate through the membrane Hydrophilic end: phosphate = polar Hydrophobic end: fatty acid = non-polar
Transport through membranes Active: ATP needed / proteins are used as pumps to move substances against the concentration gradient. Passive: no ATP needed / small particles cross the membrane through special proteins or lipid bilayer
Passive Transport Diffusion: movement of particles through the lipid bilayer from an area of high concentration to an area of low concentration O2, H2O, urea, glycerol, CO2 Facilitated Diffusion: diffusion of particles through special transport proteins charged molecules (even small ones) and large uncharged molecules Na+, K+, glucose
Passive Transport Osmosis: diffusion of water across a semi-permeablemembrane: plasma membrane permeable to water but not to solute Solute = dissolved particle Solvent = liquid medium in which particles may be dissolved
from low solute concentration to high solute concentration
Solutions can be...
Isotonic: The solutions being compared have equal concentration of solutes.
Hypertonic: The solution with the higher concentration of solutes.
Hypotonic: The solution with the lower concentration of solutes.
Active Transport Movement across membrane against concentration or electrochemical gradient (from low to high concentrations ) Requires: specific integral membrane proteins requires energy to overcome the concentration and electrochemical gradient It is used to pump specific compounds in or out of the cell Example: sodium, potassium, calcium It allows cells to accumulate needed substances even when the concentration is lower outside
The K+/Na+ Pump: An example of Active Transport Essential for the nerve impulse to be produced The pump is an integral membrane protein Cellular [K+] is high and [Na+] is low Protein pumps K+ in and Na+out This pump works independent of concentration gradient K+/Na+ Pump