Membrane Structure and Function

Cell TransportConcentrationGradient

Energy Protein Pump

Special Transport

Diffusion

High to Low(only gases CO2

and O2)

Passive (no Energy Required)

no N/A

Osmosis High to LowWater moves

Passive(no Energy Required)

no N/A

Facilitates Diffusion

High to Low

Protein PumpPassive (no Energy Required)

Yes Charge

d IONS Big

molecules

N/A

Active Transport

Low to High

Protein Pump Uses ATP for energy

YesSodium /potassium pump in nerves

ExocytosisEndocytosis Pinocytosi

s is cell drinking

Phagocytosis is cell eating

Membraneshave selective permeability - some substances cross the membrane more easily thanothersthe hydrophobic region allows passage of non-polar molecules (O2) and restrictspassage of ions and polar molecules (hydrophilic).polar and uncharged molecules such as water and CO2 are small enough to passbetween the lipid molecules.other hydrophilic molecules avoid contact with the hydrophobic lipid bilayermolecules by interacting with transport proteins. These proteins are very specificand selective in what they will transport

Fluid mosaic modelcurrently accepted membrane modelMembrane components are arranged in a phospholipid bilayer with proteins embeddedin or associated with embedded proteins.The membrane structureis dynamic and changing

II. Membrane Components1. Lipids (phospholipid)basic fabric of the membrane – phospholipids are amphipathic molecules that containboth hydrophobic and hydrophilic portions

2. Proteins- (Facilitated Diffusion)FunctionsTransportEnzymesReceptorsIntracellular junctionsCell to cell recognition - sorting of cells - tissue formation, foreign cells - immunesystem

II Mechanisms of Membrane Transport1. Passive Transport - diffusion of a substance across a biological membranea) Diffusion Diffusion is movement from an area of high concentration to low concentrationis a spontaneous process that decreases free energy of the system, which willeventually reach a dynamic equilibrium.many substances move across the membrane by diffusion e.g., O2 in respiring cells.b) Osmosis Osmosis is a form of passive transport defined by the movement of water across aselectively permeable membrane (water moves from low Concentration to high Concentration)The direction of water movement is determined by the difference in total salt concentration.hypotonic solution (lower solute concentration) hypertonic solution (higher solute concentration).isotonic- An equilibrium established when solutions on both sides of the membrane are of equal solute concentrations

Transport proteins (Facilitated Diffusion) function by producing a specific corridor or channel. ( basketball hoop)Carrier protein with a handle

Transport that Uses Energy2. Active TransportCellular energy (i.e., ATP) is expended to move substances across the membraneagainst thier concentration gradient.Animal cells maintain steep gradients of K+ (higher inside cell) and Na+ (higher outsidecell) with the aid of a sodium – potassium pump.

c) Transport of large moleculesexocytosis - secretion of large molecules by vesicles fusing with the membrane

endocytosis - cell brings in macromolecules and particulate matter by forming vesiclesfrom the plasma membrane. There are three types of endocytosis

i) phagocytosis (cellular eating) - cell develops pseudopodia which surround andengulf in a membrane bound sac large enough to be called a vacuole - fuses withlysosomesii) pinocytosis (cellular drinking) - gulps droplets of extracellular fluid – unspecific

Endocytosis Exocytosis

Sodium-potassium pumps, endocytosis, and exocytosis all involve active transport.Which of the following is a characteristic of active transport?F. It involves facilitated diffusion.G. It requires energy from the cell.H. It relies on vesicles that often function as pumps.I. It moves substances with a concentration gradient.A student places a bunch of grapes in a bowl of plain water and a second bunchof grapes in a bowl of salt water. After an hour, the grapes in the plain water areswollen, whereas the grapes in the salt water are shriveled. What cellular processcaused the grapes to shrivel?F. active transportG. diffusionH. exocytosisI. osmosis