Unit G: Membrane Transport Unit G: Membrane Transport

Standards Unit G: Membrane Transport I can recognize the fluid mosaic model and accurately identify and describe the function of the components. I can compare and contrast the various ways substances cross the cell membrane. I can recognize the various ways substances cross the membrane and provide examples from the human body for each. I can predict changes to a cell mass and size placed in solutions of differing concentrations I can use data to create a graph to show the relationship between concentration and mass. I can use a graph to extrapolate the concentration that is isotonic to a cell.

Crash Course: Membranes and Transport

MEMBRANE STRUCTURE AND FUNCTION Membranes organize the chemical activities of cells Membranes provide structural order for metabolism The plasma membrane of the cell is selectively permeable controlling the flow of substances into or out of the cell Cytoplasm Outside of cell TEM 200,000 

Membrane phospholipids form a bilayer CH2 CH3 CH N + O O– P C Phosphate group Symbol Hydrophilic head Hydrophobic tails Membrane phospholipids form a bilayer Phospholipids have a hydrophilic head and two hydrophobic tails and are the main structural components of membranes Phospholipids form a two-layer sheet called a phospholipid bilayer, with the heads facing outward and the tails facing inward Water Hydrophilic heads Hydrophobic tails

The membrane is a fluid mosaic of phospholipids and proteins A membrane is a fluid mosaic with proteins and other molecules embedded in a phospholipid bilayer where the phospholipids are constantly moving and shifting (FLUID) Membrane proteins are located studded within the membrane giving it a mosaic appearance (MOSAIC) Fibers of the extracellular matrix Carbohydrate (of glycoprotein) Glycoprotein Microfilaments of cytoskeleton Phospholipid Cholesterol Proteins Plasma membrane Glycolipid Cytoplasm

Proteins make the membrane a mosaic of functions Many membrane proteins function as enzymes Other membrane proteins function as receptors for chemical messages from other cells Membrane proteins also function in transport moving substances across the membrane ATP Messenger molecule Receptor Activated molecule

Passive transport is diffusion across a membrane In passive transport, substances diffuse through membranes without work (energy) by the cell spreading from areas of high concentration to areas of low concentration Small nonpolar molecules such as O2 and CO2 diffuse easily across the phospholipid bilayer of a membrane Equilibrium Membrane Molecules of dye

Transport proteins may facilitate diffusion across membranes Many kinds of molecules do not diffuse freely across membranes For these molecules, transport proteins provide passage across membranes through a process called facilitated diffusion Solute molecule Transport protein

Osmosis is the diffusion of water across a membrane In osmosis water travels from a solution of lower solute concentration to one of higher solute concentration Why would water move in this direction? Lower concentration of solute Higher concentration of solute Equal concentration of solute H2O Solute molecule Selectively permeable membrane Water molecule Solute molecule with cluster of water molecules Net flow of water

Water balance between cells and their surroundings is crucial to organisms The control of water balance is called osmoregulation Osmosis causes cells to shrink in hypertonic solutions and swell in hypotonic solutions In hypertonic solutions animals cells are shriveled and plants cells are plasmolyzed – why does this happen? In hypotonic solutions animal cells burst/lysis and plant cells are in turgid (their ideal state) – why does this happen? In isotonic solutions animal cells are normal, but plant cells are limp – why?? Plant cell H2O Plasma membrane (1) Normal (2) Lysed (3) Shriveled (4) Flaccid (5) Turgid (6) Shriveled (plasmolyzed) Isotonic solution Hypotonic solution Hypertonic solution Animal cell

Cells expend energy for active transport Transport proteins can move solutes against a concentration gradient through active transport, which requires ATP P Protein changes shape Phosphate detaches ATP ADP Solute Transport protein Solute binding 1 Phosphorylation 2 Transport 3 Protein reversion 4

Exocytosis and endocytosis transport large molecules To move large molecules or particles through a membrane A vesicle may fuse with the membrane and expel its contents (exocytosis) Fluid outside cell Cytoplasm Protein Vesicle

Membranes may fold inward enclosing material from the outside (endocytosis) Vesicle forming

Endocytosis can occur in three ways Phagocytosis Pinocytosis Receptor-mediated endocytosis Pseudopodium of amoeba Food being ingested Phagocytosis Pinocytosis Receptor-mediated endocytosis Material bound to receptor proteins PIT Cytoplasm Plasma membrane TEM 54,000 TEM 96,500  LM 230

CONNECTION Faulty membranes can overload the blood with cholesterol Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors LDL particle Protein Phospholipid outer layer Cytoplasm Receptor protein Plasma membrane Vesicle Cholesterol

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