Membranes and Transport Ch. 6;

What does the Membrane Do? Support  keeps cell shape Transport  moves material in and out of the cell Recognition  receives info on material around the cell Communication  send info to outside of cell Adherence  stick cell to other materials; hold it in place

Membrane Structure What are the parts? 1) Phospholipids  hydrophilic and hydrophobic ends; 2 layers 2) Sterols  non-polar rings and polar alcohol groups; cholesterol 3) Embedded proteins  do all the jobs of the membrane 4) Glycolipids and glycoproteins  protective coat or communication

Fluid Mosaic Model Membrane and it proteins are in a semi-fluid state which allows proteins to move freely in all directions How do cells maintain fluidity at low temps? – More unsaturated fatty acid chains – Raise cholesterol levels How do cells maintain stability at high temps? – Cholesterol reduces fluidity of the membrane; nonpolar region keep nonpolar tails close together

How do we know it is fluid? Frye and Edidin; 1970 Created antibodies for human (glow red) and mice (glow green) proteins Mixed human and cell membranes and watched the red and green lights over time After 40 mins the lights went from half an half to completely diffused around the membrane Found membrane fluidity is similar to machine oil

Membrane Proteins 4 Types of proteins: 1)Transport  move H 2 O, ions, and molecules 2)Recognition  cell recognize each other in a system; communication 3)Receptor  bind to signal molecules from the environment 4)Adhesion  bind cells to each other or other materials

Two Structures 1)Integral  cross through both layers of the membrane; all 4 types 2)Peripheral  bind to one side of the membrane, mostly the inside, through non-covalent bonds; cytoskeleton parts, glycolipids, and glycoproteins

How do we know these types exist? Freeze faction experiments: – Cool cell down and cut apart membrane layer – Under an electron microscope, holes and dents in the membranes match like puzzle pieces

Transportation through the Membrane Transport of material is the most activity role of the membrane Always must be: – Directional  in or out – Specific  only one type of cargo 2 Ways to Go: 1) Passive  requires no energy 2) Active  requires energy for at least one step

Passive Transport All movement “requires” energy Where does the energy come from for passive transport? – entropy (increase randomness) Diffusion  uses concentration gradients (High  Low) as a free energy source Is it directional? – Yes, though molecules move in all directions, the over movement is from high to low What happens when the gradient levels out? – Dynamic equilibrium

Simple Diffusion What can diffuse through the membrane? 1)Non-polar molecules  can pass through hydrophobic barrier in the middle Steroid hormones 2)Inorganic gases  O 2, N 2, and CO 2 3)H 2 O? – If water is polar why does it diffuse? It is small enough to pass though the phospholipids but very slowly – Water needs a little help

Facilitated Diffusion 1) Aquaporins  water channels Billion/sec 2) Ion channels  Na +, Ca 2+, and K + 2 types: Gated Channels  have to be opened by a stimulus that changes proteins shape Carrier Proteins  doors that allow one solute at a time (uniport) What is the rate limiter for facilitated diffusion? – saturation  all the doors are full; can only go so fast

Osmosis Movement of H 2 O is controlled by the osmotic pressure of the solutions in and outside the cell The greater the difference in non-diffusing solutes the stronger the pressure 3 solution types: 1)Hypotonic  low concentration outside the cell; water flows into the cell (turgor pressure) 2)Hypertonic  high concentration outside the cell; water flows out of the cell (plasmolysis) 3)Isotonic  equal concentrations

Active Transport Any transportation that requires energy 3 main functions: 1)Brining important nutrients into the cell 2)Removing waster from the cell 3)Maintaining concentrations of ions across the membrane What ions are most important? – H +, Na +, K +, and Ca 2+ – Ions create membrane potential  electrical potential difference between sides of membranes

Primary Active Transport Transport protein is same one hydrolyzing ATP H + Pumps: – Connects to ATP synthase enzymes to power ATP production – What other membrane would need H + regulation? Lysosome; need low pH Ca 2+ Pumps: – Ca 2+ concentration is high inside vesicles – Release of Ca 2+ can regulate muscle contractions, microtubule assembly, and even secretions from the cell

Primary Active Transport Na + /K + Pumps: – Essential for all animal cells and the nerve system of complex organisms – 1 ATP  3 Na + out and 2 K + in – Generates membrane potentials from -20mV to – 200mV Electrochemical gradient  concentration gradient produces both a movement of chemicals and an electrical charge

Secondary Active Transport Transport protein uses gradient produced by another protein using ATP 2 methods: 1)Symport  solutes follow in the same direction of the ion gradient (cotransport) – Ions flow into the cell and glucose follows 2)Antiport  ions flow in one direction to generate the energy to transport the solutes in the other direction – Na + /Ca 2+ exchanger removes Ca 2+ from cell by inward flow of Na + ions – Na + gradient produced by Na + /K + pump

Large Molecule Transport Exocytosis: – Remove waste material and release secretions – Vesicle fuses with plasma membrane What limits exocytosis rates? – Cell size; plasma membrane can only grow to a certain point Endocytosis: – Bulk-phase (pinocytosis) – Cell pulls in part of ECF through the vesicle; non-specific What might trigger this? – Cytosol is too thick; lack of general nutrition; reduce plasma membrane

Large Molecule Transport Receptor mediated Endocytosis – Receptor protein in membrane binds to specific substrate – Receptors form coated pit (clathrin) after activation and pull in molecule – Bind to lysosome to breakdown contents Phagocytosis  “cell eating” – Cell consumes whole other bacteria cell for energy or defense (white blood cells)

Homework Read Ch. 7 Ch. 6 vocabulary Test your Knowledge for Ch. 6 and do the “Express your Opinion” and “Interpret the Data” in your notebook.