MEMBRANE STRUCTURE AND FUNCTION CHAPTER 7 PART 2

CELL-TO-CELL RECOGNITION Carbohydrates are often used for ID Glycolipids – carbs bound to lipids Glycoproteins – carbs bound to proteins (most) Important for: Cell sorting in embryo Immune responses Blood types

MEMBRANE SYNTHESIS Molecules on the inside of the ER end up on the outside of the membrane

MEMBRANE PERMEABILITY Moves easily Nonpolar molecules (hydrophobic) Hydrocarbons, CO 2, O 2 Doesn’t move easily Polar molecules (hydrophilic) Glucose, water Charged molecules surrounded by water Ions

AQUAPORINS 3 billion water molecules per second single file Without them, H 2 O would diffuse slowly through the membrane

DIFFUSION Passive Transport – requires no energy Substances move from high to low concentration Down the concentration gradient

OSMOSIS Diffusion of water across a selectively permeable membrane Difference in FREE WATER CONCENTRATION causes it to move

OSMOSIS

CELLS WITHOUT WALLS Tonicity – ability of cell to gain or lose water Isotonic “iso” = same No NET movement of water No change in cell size

CELLS WITHOUT WALLS Hypertonic Hyper = more (solutes) Water moves out Cell will shrink

CELLS WITHOUT WALLS Hypotonic Hypo = “less” (solute) Water moves in Cell size increases Cell will swell and burst

OSMOREGULATION Organisms that live in hyper or hypo tonic environments have special adaptations Ex: Paramecium contractile vacuole

CELLS WITH WALLS Hypotonic – turgid “very firm” Isotonic – flaccid “limp” Hypertonic – plasmolysis Membrane pulls away from wall Plant wilts

FACILITATED DIFFUSION Passive transport with the help of proteins Channel proteins Aquaporins Ion Channels Gated channels open in response to a stimulus

ACTIVE TRANSPORT Move things against the concentration gradient Uses energy Sodium-potassium pump

MEMBRANE POTENTIAL Voltage across the membrane -50 to -200 mV (inside negative) Energy source for all movement Favors cations in, anions out

ION DIFFUSION Electrochemical gradient Chemical force – ions concentration gradient Electrical force – membrane potential

COTRANSPORT Substance that was pumped across the membrane does work as it comes back Brings another molecule with it

BULK TRANSPORT Exocytosis Transport vesicle from Golgi moves along microtubules toward plasma membrane Endocytosis Cell takes in molecules and matter by forming new vesicles Phagocytosis “eating” Pinocytosis “drinking” Receptor-Mediated Endocytosis

BULK TRANSPORT Exocytosis Transport vesicle from Golgi moves along microtubules toward plasma membrane Endocytosis

BULK TRANSPORT

Endocytosis

LIGANDS A molecule that binds to a receptor site of another molecule Ex: LDL