Lecture 3 Outline (Ch. 7) I.Plasma Membrane Features (pp ) II.Transport Across Membranes (pp ) A. Simple diffusion B. Facilitated diffusion C. Osmosis D. Active transport E. Example of osmosis in plant and animal cells III. Before next class: review this lecture and regions of text, fill out table on second to last slide, work the problem on the last slide (same as #6, pg. 140)

Membrane structure

Membranes are fluid: Why might a phospholipid be more likely to move within a layer than between layers? Membrane structure

cell can alter fatty acid tail saturation  affects fluidity cholesterol keeps membrane fluid at different temperatures Membrane structure

Caribou in Northern Canada in the winter More saturated fatty acids in the cell membranes Many unsaturated fatty acids in the cell membranes

The ratios of saturated to unsaturated phospholipids in a cell membrane can be changed by the organism in response to the environment. a. How do properties of a cell membrane with a high % unsaturated phospholipids compare with a membrane with a low % of unsaturated phospholipids? b. Would you expect a pond amoeba in a cold northern climate to have a higher or lower percentage of saturated phospholipids in its membranes during winter? Explain. How would this change in the summer?

“fluid mosaic model” – 1970s Integral Peripheral Glycoproteins Glycolipids Membrane structure

Remember secondary and tertiary protein structure?! Membrane Proteins

Transport Across Membranes Types of transport: A.Passive transport 1. simple diffusion 2. osmosis 3. other facilitated diffusion B.Active transport Keep track: Is Energy Required? Direction of Movement? Require a transport protein?

Selectively Permeable Membranes Small, non-polar molecules can move by simple diffusion Passive transport 1: Simple diffusion

Selectively Permeable Membranes Large or charged molecules need help crossing membrane What are some differences that seem to be depicted between these two membrane proteins?

Use transport proteins - channel or carrier proteins DOWN concentration gradient - Large, charged, polar (sugar, ions, water) NO ENERGY required Passive transport 2: Facilitated diffusion Selectively Permeable Membranes

osmosis – movement of water across cell membrane water moves via special channels called aquaporins Facilitation Diffusion example - Osmosis water moves into/out of cell until solute concentration is balanced osmosis is a type of diffusion

Active Transport Proton/sucrose pump Sodium/potassium pump

What characteristics of the cell membrane determine what gets into the cell and what doesn’t? That is, what determines cell permeability? a. If a cell membrane were composed of a phospholipid bilayer only, what molecules could move in and out? b. What different roles or functions do membrane proteins serve? c. Why are some cell types more permeable to a substance (ex: sodium ions) than others?

tonicity – # solutes in solution in relation to cell - isotonic – equal solutes in solution - hypertonic – more solutes in solution animal cell plant cell - hypotonic – fewer solutes in solution Osmosis in plant and animal cells

Paramecium example regulate water balance water into contractile vacuole – then water expelled pond water hypotonic Osmosis in protist cells

Think about simple diffusion, facilitated diffusion, and active transport. How does each occur across the membrane? Energy required? a. What functions might each of the three types of membrane transport serve in a paramecium? b. What functions might each of the three types of membrane transport serve in a human or a tree?

Self-Check Type of transport Energy required? Movement direction? Examples: Simple diffusionnodown conc. gradientO 2, CO 2, non- polar molecules Osmosis Facilitated diffusion Active transport Co-transport

A fake “cell” (a selectively permeable membrane enclosing an aqueous solution) is in a beaker as shown below. The membrane is permeable to glucose and fructose (monosaccharides) but not to sucrose (a disaccharide). 0.03M sucrose 0.02M glucose 0.01M sucrose 0.01M glucose 0.01M fructose Questions: 1.Use arrows to show the net movements of solute into/out of the cell 2.Is the solution outside the cell hypertonic, isotonic, or hypotonic? 3.Will osmosis occur? Which direction? 4.What will happen to the fake cell? 5.Eventually, will the two solutions (inside and outside the cell) have the same concentrations?