Unit G: Membrane Transport

1. 0 Unit G: Membrane Transport

2. 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.

3. Crash Course: Membranes and Transport

4. Outside of cell Cytoplasm TEM 200,000  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

5. CH3 Hydrophilic head + N CH2 CH3 CH3 CH2 Phosphategroup O P O– O O CH CH2 CH2 O O O O C C CH2 CH2 CH2 CH2 Water CH2 CH2 Hydrophilicheads CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 Symbol Hydrophobictails CH CH2 CH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 Water CH3 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

6. Fibers of the extracellular matrix Carbohydrate(of glycoprotein) Glycoprotein Glycolipid Plasmamembrane Phospholipid Proteins Cholesterol Microfilamentsof cytoskeleton Cytoplasm 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)

7. Messenger molecule Receptor ATP Activatedmolecule 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

8. Molecules of dye Membrane Equilibrium Equilibrium 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

9. Solutemolecule Transportprotein 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

10. Equalconcentrationof solute Higherconcentrationof solute Lowerconcentrationof solute H2O Solutemolecule Selectivelypermeablemembrane Watermolecule Solute molecule with cluster of water molecules Net flow of water 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?

11. Hypertonic solution Hypotonic solution Isotonic solution H2O H2O H2O H2O Animalcell (3) Shriveled (2) Lysed (1) Normal Plasmamembrane H2O H2O H2O H2O Plantcell (6) Shriveled (plasmolyzed) (5) Turgid (4) Flaccid 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??

12. Transportprotein P P P Phosphatedetaches Proteinchanges shape ATP Solute ADP Transport 1 Solute binding 2 Phosphorylation 3 4 Protein reversion Cells expend energy for active transport • Transport proteins can move solutes against a concentration gradient through active transport, which requires ATP

13. Fluid outside cell Vesicle Protein Cytoplasm 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)

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

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

16. Phospholipid outer layer LDL particle Vesicle Cholesterol Protein Plasmamembrane Receptorprotein Cytoplasm CONNECTION • Faulty membranes can overload the blood with cholesterol • Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors

17. Salt Shakedown • https://www.cbc.ca/marketplace/episodes/2012-2013/the-great-salt-shakedown