Problem of the Day:  Identify the cells below as prokaryotic, plant or animal. Explain why.:

Problem of the day: Using what you have learned about surface area to volume ratios, why do you think that cold areas have more large mammals and less small mammals? Why would a larger than average human species have a harder time surviving in a warming world?

Chapter 7: Membrane Structure and Function You Must Know:  Why membranes are selectively permeable  The role of phospholipids, proteins, and carbohydrates in membranes  How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution  How electrochemical gradients are formed

Essential Knowledge 2.B.1 Cell membranes are selectively permeable due to their structure. (be able to explain how)

Membrane structure, I  Selective permeability- allows some substances to cross more easily than others  Amphipathic~ l Hydrophilic phosphate portions oriented toward aqueous external/internal environments l Hydrophobic fatty acid portions face each other within the interior of the membrane itself

Lipid Function  Phospholipids – amphipathic, bilayer, major structural component, barrier  Cholesterol – modulates fluidity

Membrane structure, II  Phospholipids~ membrane fluidity; hydrophobic barrier that separates cell from environment  Cholesterol~ membrane stabilization  Integral proteins~ trans membrane proteins  Peripheral proteins~ surface of membrane  Membrane carbohydrates ~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins; an example-ABO blood types are glycoproteins  Embedded proteins can be hydrophilic or hydrophobic  Fluid Mosaic Model describes the membrane as fluid with proteins embedded in the phospholipid bilayer.

Plant cells wall are made of cellulose and are external to the cell membrane. (prokaryotes and fungi cell walls are also external to the cell membrane)

Membrane structure, III  Membrane protein function:  transport (example aquaporins)  enzymatic activity  signal transduction  intercellular joining  cell-cell recognition  ECM attachment

Traffic Across the Membranes  Membrane is selectively permeable l The membrane has holes/channels that only certain particles can fit through l Passive transport-goes with the concentration gradient (w/ or w/o membrane proteins l Active transport-goes against concentration gradient; requires membrane protein and energy l Nutrients need to move in and wastes need to move out

Passive Transport-Diffusion  Diffusion-material moves down the gradient; does not require energy  Osmosis-water diffusion  Primary role in import of resources and export of wastes  Particles must be 1) small 2) nonpolar-Why? (hydrocarbons, carbon dioxide, oxygen) 3) uncharged

Passive Transport-Facilitated Diffusion  Requires transport protein  Still down the gradient  Used for: 1) charged particles 2) LARGE particles 3) polar molecules (glucose, water, ions)  Aquaporins-embedded channel proteins used for large polar molecules and ions; greatly accelerate the speed with which water molecules can cross the membrane a.Channel protein b.Carrier protein

Direction of Flow  Diffusion~ tendency of any molecule to spread out into available space  Osmosis~ the diffusion of water across a selectively permeable membrane  Hypotonic, hypertonic, and isotonic are relative terms comparing a solution on one side of the semipermeable membrane to a solution on the other side Hypertonic-more solute molecules, less water molecules than the cell Hypotonic-less solute molecules, more water molecules than the cell Isotonic-equal concentrations of solute and water molecules Water level goes up on right side of tube because only water molecules can move through the membrane

Water balance  Osmoregulation~ control of water balance  Hypertonic~ higher concentration of solutes than cell  Hypotonic~ lower concentration of solutes than cell  Isotonic~ equal concentrations of solutes Cells with Walls:  Turgid (very firm)  Flaccid (limp)  Plasmolysis~ plasma membrane pulls away from cell wall

Water Potential  Predicts the way water diffuses through tissues  Calculated from solute potential and pressure potential

Pre-lab question: 4 potato cores were weighed and placed (overnight) in sucrose solutions of the molarities indicated on the graph. The next day they were blotted dry and weighed. The % increase or decrease in mass was calculated and graphed vs. the sucrose molarity. All solutions were at 25°C. Determine the solute potential of the potato cores to the nearest tenth. Ψ = Ψ P + Ψ S Ψ S = -iCRT Formula sheet will give you R. T is temp for Kelvin Answer: -1(.3)(.0831)(298) = -7.4

From a region of: To a region of: Higher water potentialLower water potential Lower solute concentrationHigher solute concentration Hypotonic solution (less solute)Hypertonic solution (more solute) Lower osmotic potentialHigher osmotic potential The Direction of Water Movement in Osmosis

Active Transport  requires cellular energy (ATP)  Against the gradient(low to high concentration)  Requires membrane proteins  Ion pumps-Na/K, electrogenic  Cotransport  Exocytosis and Endocytosis  Phagocytosis and pinocytosis  Receptor mediated endocytosis The above picture is an electrogenic pump, used to store energy to drive other processes like the uptake of nutrients.

Electrogenic Pumps on cell membranes  Electrogenic pump-a transport protein that generates voltage across a membrane  Cytoplasm has a negative charge compared to extracellular fluid= membrane potential  Acts like a battery-the membrane potential favors the passive transport of cations into the cell and anions out of the cell=electrochemical gradient  Stores energy used for cotransport  Goes AGAINST the concentration gradient  Examples are the sodium potassium pump and the proton pump

Chemiosmosis-use of an electrogenic pump within the membranes of mitochondria and chloroplasts; proton pumpproton pump

Sodium Potassium Pump Sodium concentration is high outside the cell and low inside, while potassium ion concentration is low outside the cell and high inside, so the pump is working AGAINST the gradient. This generates voltage by pumping 3 sodium ions out for every 2 potassium ions in.

Endocytosis and exocytosis move large molecules across the membrane. Endocytosis  The cell takes in macromolecules and particulate matter by forming new vesicles derived from the plasma membrane  Phagocytosis-cellular eating  Pinocytosis-cellular drinking  Receptor mediated endocytosis-very specific Exocytosis  Internal vesicles fuse with the plasma membrane to secrete large macromolecules out of the cell.