What did you observe about membrane behavior from this video? The Cell Membrane What did you observe about membrane behavior from this video?

Movement Across Membranes Cell membrane is selectively permeable: Small, non-lipid soluble molecules (water) Look at the membrane model again. How do you think the following materials get in/out?: Small, lipid soluble molecules (hydrocarbons) Macromolecules (starches) Large, nonpolar molecules (glucose)

Effect of Phospholipid Structure

Fluidity Watch the membranes – are they rigid? If not, how do they move? Rate molecules move within & across membranes depends on temperature structure of hydrocarbon tails in bilayer

Membrane Transport

Solute Movement across Lipid Bilayers Materials move across membrane in different ways. 1. Passive transport does not require energy input 2. Active transport energy required for substances to cross the membrane. Small molecules and ions in solution are called solutes, have thermal energy, and are in constant, random motion. Differences in solute concentration across the membrane create a concentration gradient Molecules and ions move randomly when a concentration gradient exists, but there is a net movement from high- concentration regions to low-concentration regions. Diffusion along a concentration gradient increases entropy and is thus spontaneous.

Goal? Reaching Equilibrium! One way to do this is diffusion – direct movement of solutes from areas of high to low concentration NO energy required = PASSIVE transport

Osmosis Does water move towards high solute concentration? Low solute concentration? Does water concentration move from high to low or low to high concentration?

Hyper-, Hypo-, & Isotonic

Let’s practice

Hyper-, Hypo-, or Isotonic? (in your notes) Use arrows to show the direction of water movement into or out of each cell.

Label the Plant Cell What type of solution are they in?

Label the Red Blood Cells Why should you worry about this? What type of solution are they in?

Membrane Proteins Affect Ions and Molecules Transmembrane proteins that transport molecules are transport proteins. THREE broad classes of transport proteins; each affects membrane permeability: Channels Carrier proteins or transporters Pumps

Movement affects gradient, affects continued movement

Facilitated Diffusion vs. Pumps Facilitated diffusion – PASSIVE transport of substances using specific channel proteins Ex: GLUT-1 transport protein increases permeability of membrane to glucose Protein Pumps – ACTIVE transport using ATP to move substances against concentration gradient Ex: Sodium/Potassium Pump transports Na+ & K+ against electrochemical gradient

Active Transport: Pumps This can set up a gradient that “switches” on the transport of other materials. This is called secondary transport or cotransport.

Active Transport: Endo/Exocytosis

Summary of Membrane Transport Give examples of types of transport across the membrane. Diffusion and facilitated diffusion are forms of ________transport and thus move materials down their concentration gradient and ________require an input of energy. ______transport moves materials against their concentration gradient and _______energy provided by _____or an electrochemical gradient.

Homework Scenario Intraveneous solutions must be prepared so they are isotonic to red blood cells. A 0.9% salt solution is isotonic to red blood cells. a. Explain what would happen if you placed a red blood cell in a solution of 99.3% water and 0.7% salt. b. Explain what would happen if you placed a red blood cell into a solution of 90% water and 10% salt.

2. What would happen to a cell if placed in the following solutions 2. What would happen to a cell if placed in the following solutions? Explain in detail and illustrate. Hypotonic Isotonic Hypertonic

Water Potential Tendency of water to move in a direction (dependent on solute concentration & pressure) Water potential of 0 is high - as add solute & pressure becomes more negative - more negative number, more potential to move water - occasionally a positive number

Just like water moves from high concentration to low concentration (down the concentration gradient) water will move from high water potential to low water potential. Ex: distilled water (no ions) has a water potential of 0.

Increase solute decrease water potential Increase pressure increases water potential When osmosis occurs water will move to areas where water potential is lower. Ex: hypertonic: low H2O potential hypotonic: high H2O potential

Water potential calculation Ψ = - i C R T i = Ionization constant (1 for sucrose) C = Molar concentration of solute (from lab) R = Pressure constant (0.0831 liter bars/mole K) T = Temperature K (273 + °C of solution) **pressure potential usually 0, do not take into account **