Why is cholesterol an important feature of the cell membrane? I’m Matthew Do Now 10/29 Why is cholesterol an important feature of the cell membrane?

10/27 Study on your own for a few minutes- quiz today on prokaryotic/eukaryotic cells AND organelles!

10/30 You have a cell, with a semi permeable membrane and a 1.5% potassium concentration. You put it into a solution of 2% potassium. What adjective describes the solution? What direction would you expect water to flow? What do you expect to see happen to the cell?

Transport in/out of cells

Cell membrane: Made of Phospholipids Phosphate “attracted to water” Phosphate head Hydrophilic: attracted to water Fatty acid tails Hydrophobic: repelled by water Arranged as a bilayer Fatty acid “repelled by water”

Cell membrane defines cell Cell membrane separates living cell from environment Controls traffic in & out of the cell allows some substances to cross more easily than others =semi-permeable

Cell membrane is more than lipids… Proteins embedded in phospholipid bilayer Create channels protein channels in lipid bilyer membrane

Any Questions?? http://www.youtube.com/watch?v=LKN5sq5dtW4

Movement across the Cell Membrane 2007-2008

Concentration of Solutions: How much solute is dissolved in the solvent Unit is usually in grams/liter Sometimes reported in a percentage (%) or in Molarity (M)

Concentration Gradient When one side of the cell has a much higher concentration than the other side of the cell Equilibrium: Solutes move to make both sides the same concentration

Types of Transport: 1. Simple Diffusion Move from HIGH to LOW concentration no energy needed

2. Facilitated Diffusion facilitated = with help Diffusion through protein channels (HIGH to LOW concentration) channels move specific molecules across cell membrane no energy needed Donuts! Each transport protein is specific as to the substances that it will translocate (move). For example, the glucose transport protein in the liver will carry glucose from the blood to the cytoplasm, but not fructose, its structural isomer. Some transport proteins have a hydrophilic channel that certain molecules or ions can use as a tunnel through the membrane -- simply provide corridors allowing a specific molecule or ion to cross the membrane. These channel proteins allow fast transport. For example, water channel proteins, aquaporins, facilitate massive amounts of diffusion.

3. Active Transport Cells may need to move molecules against concentration gradient (LOW to HIGH) Proteins transports solute from one side of membrane to other protein “pump” Uses energy Some transport proteins do not provide channels but appear to actually translocate the solute-binding site and solute across the membrane as the protein changes shape. These shape changes could be triggered by the binding and release of the transported molecule. This is model for active transport.

Transport summary simple diffusion facilitated diffusion ATP active transport

The Special Case of Water Movement of water across the cell membrane 2007-2008

4. Osmosis: is just diffusion of water Water is very important to life, so we talk about water separately Diffusion of water from HIGH concentration of water to LOW concentration of water

Concentration of water Direction of osmosis is determined by comparing total solute concentrations Hypertonic - more solute, less water Hypotonic - less solute, more water Isotonic - equal solute, equal water hypotonic hypertonic water overall movement of water

Do you understand Osmosis… Cell (compared to beaker)  hypertonic or hypotonic Beaker (compared to cell)  hypertonic or hypotonic Which way does the water flow?  in or out of cell

Any Questions??