Bell work 10/29/2012 Answer-

Today’s Objectives Distinguish between diffusion and osmosis. Explain how substance cross the cell membrane through facilitated diffusion Explain how ion channels assist the diffusion of ions across the cell membrane.

The Cell Membrane

Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

Filaments of cytoskeleton Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Glycoprotein Extracellular fluid Glycolipid Transmembrane proteins The carbohydrates are not inserted into the membrane -- they are too hydrophilic for that. They are attached to embedded proteins -- glycoproteins. Phospholipids Filaments of cytoskeleton Cholesterol Peripheral protein Cytoplasm

Membrane Proteins Proteins determine membrane’s specific functions cell membrane & organelle membranes each have unique collections of proteins Membrane proteins: __________________________ loosely bound to surface of membrane cell surface identity marker penetrate lipid bilayer, usually across whole membrane transport proteins channels, permeases (pumps)

Movement across the Cell Membrane

Diffusion Move from _____to _____concentration movement of water ____________________ _________________ movement of water diffusion osmosis

Diffusion across cell membrane Cell membrane is the boundary between inside & outside… separates cell from its environment Can it be an impenetrable boundary? _____ OUT waste ammonia salts ______ H2O products IN food carbohydrates sugars, proteins amino acids _________ salts, _____, H2O OUT IN cell needs materials in & products or waste out

Diffusion through phospholipid bilayer What molecules can get through directly? ___________________________ What molecules can NOT get through directly? polar molecules H2O ions salts, ammonia large molecules __________, proteins lipid inside cell outside cell salt NH3 sugar aa H2O

Channels through cell membrane Membrane becomes _____________ with protein channels specific channels allow specific material across cell membrane inside cell H2O aa sugar salt outside cell NH3

Facilitated Diffusion Diffusion through protein channels channels move specific molecules across cell membrane ___________________ facilitated = with help open channel = fast transport high low 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.

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

Osmosis is diffusion of water Water is very important to life, so we talk about water separately Diffusion of water from _____ concentration of water to _____concentration of water across a semi-permeable membrane

Concentration of water Direction of osmosis is determined by comparing total solute concentrations _____________- more solute, less water _____________ - less solute, more water ___________ - equal solute, equal water hypotonic hypertonic net movement of water

Managing water balance Cell survival depends on balancing water uptake & ______ freshwater balanced saltwater

Managing water balance ______________ animal cell immersed in mild salt solution example: blood cells in blood plasma problem: none ____ net movement of water flows across membrane equally, in both directions volume of cell is stable balanced

Managing water balance _______________ a cell in fresh water example: Paramecium problem: gains water, swells & can burst water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell ATP plant cells _____________ ATP freshwater

Water regulation Contractile vacuole in Paramecium

Managing water balance __________________ a cell in salt water example: shellfish problem: lose water & die solution: take up water or pump out salt plant cells plasmolysis = ________ saltwater

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