AP Biology The Cell Membrane *Very thin ( nm) *Elastic *Semipermeable * Dynamic *lipid bilayer *Made of phospholipids, proteins, CHO& otherlipids *amphipathic

AP Biology Phospholipids Fatty acid Phosphate Flexibility & selective permeability  Fatty acid tails  hydrophobic  Phosphate group head  hydrophilic  Arranged as a bilayer

AP Biology Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

AP Biology  Protein: *Hydrophilic & hydrophobic *Integral & peripheral  Cholesterol: permeability & toughness  CHO: recognition sites & attach cells together Glycoprotein Glycolipid Peripheral protein Cholesterol

AP Biology Functions of membrane proteins  1- structural ptns  2- passive channels: ungated & gated(voltage / ligand)  3- carriers for facilitated diffusion  4- carriers for active transport (uniport /symport/ antiport)  5- receptors: number & sensitivity change  6- enzymes  7- identity ptns  8-intercellular connections: a. binding j: tight & desmosomes b. gap j  9- cell adhesion molecules  10- fixation of cytoskeleton

AP Biology Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion

AP Biology Membrane carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish one cell from another  antigens  important in organ & tissue development  basis for rejection of foreign cells by immune system

AP Biology Movement across the Cell Membrane

AP Biology Diffusion  All molecules are in constant motion  Diffusion  movement from high  low concentration  Diffusion  movement from high  low concentration

AP Biology

Facilitated Diffusion  Diffusion through protein channels  channels move specific molecules across cell membrane  no energy needed open channel = fast transport facilitated = with help high low

AP Biology Facilitated Diffusion

AP Biology Active Transport “The Doorman” conformational change  Against concentration gradient  Needs carrier protein  Energy is needed ATP low high

AP Biology symportantiport Active transport  Many models & mechanisms ATP

AP Biology Active transport  1ry active: * eg Na+/K+ pump *α &β subunits *α subunit contains 2 binding sites for K+ on the outside & 3 binding sites for Na+ on the inside & an ATP binding site *β subunit has ATPase activity.  2ry active: * eg Glucose transport 2ry to active transport of Na 1 st Na pumped out ….creates concentration gradient… Na & glucose bind a carrier…transports them to inside

AP Biology Getting through cell membrane  Passive Transport  Simple diffusion  diffusion of nonpolar, hydrophobic molecules  lipids  high  low concentration gradient  Facilitated transport  diffusion of polar, hydrophilic molecules  through a protein channel  high  low concentration gradient  Active transport  diffusion against concentration gradient  low  high  uses a protein pump  requires ATP  Vesicular transport ATP

AP Biology Transport summary simple diffusion facilitated diffusion active transport ATP

AP Biology How about large molecules?  Moving large molecules into & out of cell  through vesicles & vacuoles  endocytosis  phagocytosis = “cellular eating”  pinocytosis = “cellular drinking”  exocytosis exocytosis

AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal

AP Biology Osmosis is diffusion of water  Diffusion of water from high concentration of water to low concentration of water  across a semi-permeable membrane  The pressure necessary to stop solvent mol movements= osmotic pressure  The numbers of particles per unit volume of fluid  Measured in mmHg  Osmole osmolarity osmolality

AP Biology  The osmolarity of ICF=that ECF=300 mosmol  280 mosmol is due to Na, Cl & HCO3  20 mosmol is due to protein  Tonicity: is the osmolality of a solution relative to the plasma  Plasma proteins of blood is called oncotic pressure. It is important for capillary circulation &regulation of ECF

AP Biology Concentration of water  Direction of osmosis is determined by comparing total solute concentrations  Hypertonic - more solute, less water  Hypotonic - less solute, more water  Isotonic - equal solute, equal water hypotonichypertonic water net movement of water

AP Biology Donnan effect  The protein anions inside the cells are non diffusible hinder the diffusion of diffusible cations  More osmotically active particles inside the cell  The cell tends to swell  But the Na+/ K+ pump prevents cell rupture

AP Biology Any Questions??