Transport of molecules across cell membrane SELECTIVELY PERMEABLE in and out largechargedpolar SELECTIVELY PERMEABLE: Controls what comes in and out of the cell. Does not let large, charged or polar things through without help. functions of cell membrane (Plasma membrane) Is one of the most important functions of cell membrane (Plasma membrane) A steady traffic of small molecules and ions move across the plasma membrane in both directions. For example, sugars, amino acids, and other nutrients enter a muscle cell and metabolic waste products leave it. The cell absorbs O 2 and expels CO 2. It also regulates concentrations of inorganic ions, like Na +, K +, Ca 2+, and Cl -, by passing them across the membrane. However, substances do not move across the membrane barrier indiscriminately (randamly) . Hydrophobic molecules, like hydrocarbons, CO 2, and O 2, can dissolve in the lipid bilayer and cross easily. Ions and polar molecules, like water, glucose and sugars pass through with difficulty. Proteins can assist and regulate the transport of ions and polar molecules. Proteins can assist and regulate the transport of ions and polar molecules. Phagocytosis PinocytosisReceptor-mediatedendocytosis Cellular eating Cellular drinking Using specific receptors (coated vesicles) that bind to specific legends and engulf it. It is specific Selective eating Transport Passive Active Diffusion Osmosis Largemolecules SmallMolecules/ions (T. protein) (Membrane) (Membrane) ExocytosisEndocytosis *** Facilitateddiffusion (Membrane) Passive transport is is a kind of transport by which ions or molecules move along a concentration gradiant, ( means movement from an area of higher concentration to an area of lower concentration ) Passive Transport A process that does not require energy to move molecules from a HIGH to LOW concentration DDiffusion FFacilitated Diffusion OOsmosis Simple Diffusion: is movement ( spread ) of molecules 1) randomly 2) from areas of high concentration to areas of low concentration 3) Requires no energy For example, in case of presence of a permeable membrane separating a solution containing dye molecules from pure water, the dye molecules will cross the membrane randomly. The dye will cross the membrane until both solutions have equal concentrations of the dye (dynamic equilibrium ). The dye will cross the membrane until both solutions have equal concentrations of the dye (dynamic equilibrium ). Osmosis: is a passive transport in which water diffuses across a selectively permeable membrane from the hypotonic solution to the hypertonic solution until the solutions become isotonic Osmosis Hypertonic solution: contains high concentration of solute molecules. Hypertonic solution: contains high concentration of solute molecules. Hypotonic solution: contains low concentration of solute molecules. Hypotonic solution: contains low concentration of solute molecules. Isotonic solution: Isotonic solution: contains equal concentrations of solute molecules contains equal concentrations of solute molecules Biological MembraneHypotonicHypertonic H2OH2OH2OH2O Semi-permeable membrane is permeable to water, but not to sugar A cell in a hypotonic solution will gain water, swell, and burst. The cell in a hypertonic environment will loose water, shrivel , and die. .... Organisms without rigid walls have osmotic problems in either a hypertonic or hypotonic environment and must have adaptations for osmoregulation to maintain their internal environment. Example, Paramecium have a specialized organelle ( the contractile vacuole), that functions as a pump to force water out of the cell. Another form of passive transport Many molecules and ions diffuse passively through the lipid bilayer with the help of transport proteins The passive movement of molecules down its concentration gradient via a transport protein is called facilitated diffusion Used for molecules that are too large to cross the membrane by diffusion (i.e. glucose) Carrier proteins bind to larger molecules, and change their shape so molecules can diffuse through. Channel proteins provide water filled pores for charged ions to pass through Molecules move against the concentration gradient (low to high) Energy must be provided via ATP (even when we are resting, 40% of our energy is spent on active transport!) Uses specialized transport proteins and protein pumps Maintains internal cell environments (i.e. cells electrical gradient, roots pull in minerals from soil, filtering blood in your kidneys) The sodium-potassium pump maintains the transport of sodium (Na + ) and potassium ions (K + ) across the membrane. The animal cell has higher concentrations of K + and lower concentrations of Na + inside the cell. The sodium-potassium pump (T. protein) uses the energy of one ATP to pump 3 Na + ions out and 2 K + ions in. A- small molecules Sodium potassium pump High conc. of K + High conc. of Na + Low conc. of K + Low conc. of Na + 1ATP 3 2 T. protein down their concentration gradient against their concentration gradient Both diffusion and facilitated diffusion are forms of passive transport of molecules down their concentration gradient, while active transport requires an investment of energy to move molecules against their concentration gradient. Two roles of membrane protein *** Large molecules, such as polysaccharides and proteins, cross the membrane by vesicles This occurs by Exocytosis and Endocytosis B)- Large molecules ( ) B)- Large molecules (macromolecules ) *** Exocytosis : Exocytosis : a transport vesicle budded from the Golgi apparatus is moved by the cytoskeleton to the plasma membrane. When the two membranes come in contact , the bilayers fuse and spill the contents to the outside. *** Endocytosis the cell brings in macromolecules and particulate matter by forming new vesicles from the plasma membrane and include the following types: Endocytosis , the cell brings in macromolecules and particulate matter by forming new vesicles from the plasma membrane and include the following types: 1. Phagocytosis (solids) 2. Pinocytosis (liquids) 3. Receptor mediated A)- Phagocytosis : A)- Phagocytosis : Called cellular eating . The cell engulfs a particle by extending pseudopodia around it and packaging it in a large vacuole. The cell engulfs a particle by extending pseudopodia around it and packaging it in a large vacuole. The contents of the vacuole are digested when the vacuole fuses with a lysosome. Phagocytosis B)- Pinocytosis, B)- Pinocytosis, cellular drinking, cellular drinking, a cell creates a vesicle around droplets of extracellular fluid . extracellular fluid . This is a non-specific process . C)- Receptor-mediated endocytosis: C)- Receptor-mediated endocytosis: It Is called It Is called ( Selective eating ) is highly specific in substances are being transported. It is highly specific in substances are being transported. It is triggered when extracellular substances bind to special receptors, on the membrane surface. This triggers the formation of a vesicle It enables a cell to take large quantities of specific materials that may be in low concentrations in the environment. _zkY diffusion of food coloring_zkY NAT4 artisticNAT4 AzYc egg cell osmosisAzYc int_membraneweb/int_membraneweb/