Movement across the Cell Membrane

First free response (FRQ) The selectively permeable plasma membrane is composed of phospholipids and protein, which allow for its unique functions. A) DESCRIBE the structure and properties of phospholipids and EXPLAIN the important roles of phospholipids in the plasma membrane. B) EXPLAIN why proteins are an important component of the cell membrane, based on their structure and properties.

Diffusion Lab homework Read lab packet Highlight all vocabulary in background section Read procedures Complete #1 on page 15. TODAY: Part A Procedures on page 6 Table 1 on page 12

Iodine reacts with starch causing a blue-black color. Diffusion lab results Color Glucose Time Bag Beaker Start clear amber + - 30 minutes Iodine reacts with starch causing a blue-black color.

Part B: Make 6 cells Then…day 3 of egg lab

Part b DIFFUSION lab data This is what you graph CLASS DATA FOR % CHANGE IN MASS Water 0.2 M 0.4 M 0.6 M 0.8 M 1.0 M

#2: Iodine diffused into the bag (blue/black); Glucose diffused out of the bag into the environment; Osmosis was also occurring bc it went into the bag as glucose diffused out #3: Yes, iodine and glucose diffused, but the starch could not diffuse bc it was too big #4: Osmosis occurred which caused a net flow of water into the bag increasing its mass; More water because the environment was hypotonic (less solute). Equilibrium was reached. #5: Hypotonic because it had less solute than the bags

Change in mass water .2 M .4 M .6 M .8 M 1.0 M

Part C Class averages class avg Water 0.2 M 0.4 M 0.6 M 0.8 M 1.0 M CLASS DATA FOR % CHANGE IN MASS OF POTATOES Water 0.2 M 0.4 M 0.6 M 0.8 M 1.0 M

Percent change in mass of potatoes at different sucrose molarities individual class average % Change in Mass Sucrose Molarity (moles/liter)

PLASMOLYSIS turgor pressure https://www.youtube.com/watch?v=4JyT__Dea8Q Plant cells losing water in hypertonic solutions Shrinking Cell membrane pulls away from outer cell wall Very rare Opposite? turgor pressure

PASSIVE TRANSPORT Movement of a substance across a membrane with no energy investment Direction depends on concentration High concentrations to low concentrations DOWN or WITH its concentration gradient Types: diffusion, osmosis, facilitated diffusion Movement from high concentration of that substance to low concentration of that substance.

Diffusion Movement from high to low concentrations 2nd Law of Thermodynamics governs biological systems universe tends towards disorder (entropy) Movement from high concentration of that substance to low concentration of that substance.

movement of water diffusion osmosis

Osmosis is 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 across a semi-permeable membrane

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 net movement of water

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

Osmosis… .05 M .03 M 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

Managing water balance Isotonic animal cell immersed in mild salt solution example: blood cells in blood plasma problem: none no net movement of water flows across membrane equally, in both directions volume of cell is stable balanced

Managing water balance Hypotonic 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 turgid ATP freshwater

Water regulation Contractile vacuole in Paramecium ATP

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

Aquaporins 1991 | 2003 Water moves rapidly into & out of cells evidence that there were water channels Peter Agre John Hopkins Roderick MacKinnon Rockefeller

Diffusion across cell membrane Cell membrane is the boundary between inside & outside… separates cell from its environment NO! Can it be an impenetrable boundary? IN OUT food carbohydrates, sugars, proteins amino acids, lipids, salts, O2, H2O waste ammonia salts CO2 H2O products cell needs materials in & products or waste out

Diffusion through phospholipid bilayer What molecules can get through directly? fats & other lipids inside cell outside cell What molecules can NOT get through directly? polar molecules H2O ions salts, ammonia large molecules starches, proteins lipid salt NH3 sugar aa H2O

Channels through cell membrane Membrane becomes semi-permeable 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 no energy needed facilitated = with help open channel = fast transport 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. high low “The Bouncer”

conformational change Active Transport Cells may need to move molecules against concentration gradient shape change transports solute from one side of membrane to other protein “pump” “costs” energy = ATP conformational change 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. low high ATP “The Doorman”

Active transport Many models & mechanisms ATP ATP antiport symport Plants: nitrate & phosphate pumps in roots. Why? Nitrate for amino acids Phosphate for DNA & membranes Not coincidentally these are the main constituents of fertilizer Supplying these nutrients to plants Replenishing the soil since plants are depleting it antiport symport

Getting through cell membrane Passive Transport Simple diffusion diffusion of nonpolar, hydrophobic molecules lipids high  low concentration gradient Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel Active transport diffusion against concentration gradient low  high uses a protein pump requires ATP ATP

Transport summary simple diffusion facilitated diffusion ATP active transport

How about large molecules? Moving large molecules into & out of cell through vesicles & vacuoles endocytosis phagocytosis = “cellular eating” pinocytosis = “cellular drinking” exocytosis exocytosis

Endocytosis fuse with lysosome for digestion phagocytosis non-specific process pinocytosis triggered by molecular signal receptor-mediated endocytosis

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

Any Questions??