Introductory Questions (Lab) Suppose you have an artificial cell that was permeable to monosaccharides and impermeable to disaccharides. What would happen to the cell if it had 0.80 M maltose and 0.85 M fructose in it and was placed in a solution containing 0.45 M glucose, 0.65 M fructose, and 0.40 M sucrose. a) Which direction would the water flow? b) Which area has a higher water potential? c) What would happen to the concentration of the maltose inside the cell (increase, decrease, remain the same)? What is the ionization constant (i) for sucrose? Determine the “C” value for your potato cores. (guide sheets) Graph your results: % change in mass vs. sucrose molarity within the beakers (guide sheets)

Introductory Questions #3 1) What purpose do vesicles serve in the cell? 2) Name all of the organelles that are a part of the endomembrane system. 3) Explain how the rough ER is different from the smooth ER, How is a lysosome different from a peroxisome? How is the basal body of the flagella similar to centrioles? (see pg. 115) Name the three parts of the cytoskeleton. Which protein fiber is the smallest? Which is the largest? Which intercellular junction is composed of protein surrounding a pore allowing for ions, sugars, etc. to pass from one cell to the next? Name a similar structure in plants. What does ECM stand for? Name the most abundant glycoprotein found in the ECM. What purpose does it serve?

Introductory Questions # What purpose do protein Kinase enzymes serve in the signal transduction process? (Ch. 11 pgs. 204-210)

Dialysis Tubing Experiment

Chapter 7~ Membrane Structure & Function

Introductory Questions #4 Name the major molecules that make up the cell membrane. How thick is the membrane? How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model? Briefly explain how the membrane remains fluidic in lower temperatures? What did the freeze fracture process and electron microscope reveal about the membrane? How does cholesterol act as a “buffer” for the membrane? How does a hypotonic solution differ from a hypertonic solution? What are the three forms of endocytosis? Explain how they are different.

Introductory Questions #5 What is the charge range difference across the membrane? Which side is positive and which side is negative? Why is this the case? How is diffusion different from facilitative diffusion? Name some factors that can affect diffusion rates of molecules. Name the ions used to show how active transport works in a the cell membrane. What role does ATP play during this process?

Membrane Structure-Two Models Proposed Amphipathic Lipids~ hydrophobic & hydrophilic regions Singer-Nicholson: fluid mosaic model proposed in 1972 (Current model)

The Phospholipid Bilayer The heads face outward and the tails face inward In water, phospholipids form a stable bilayer Water Hydrophilic heads Hydrophobic tails Water Figure 5.11B

Closer View of the Cell Membrane

Membrane Structure Approx. 10 nm thick Phospholipid Bilayer -Amphipathic molecules -Saturated and Unsaturated lipids Proteins: integral &* peripheral Cholesterol-acts as a temperature buffer

Membranes organize the chemical activities of cells Membranes organize the chemical reactions making up metabolism   Cytoplasm Figure 5.10

Function of the Plasma Membrane They control the flow of substances into and out of a cell Membranes are selectively permeable **Small, Nonpolar molecules easily pass through the membrane: O2, CO2, Hormones, Steroids vs. **Large, Charged do not pass through easily and must be helped in. These molecules would include: C6H12O6 , Proteins, and Ions Membranes regulate chemical reactions and can hold teams of enzymes that function in metabolism

A Phospholipid

Membrane Phospholipids Phospholipids are the main structural components of membranes They each have a hydrophilic head and two hydrophobic tails Head Symbol Tails Figure 5.11A

Membrane Structure - 2nd Look Phospholipids~ membrane fluidity Cholesterol~ membrane stabilization “Mosaic” Structure~ Integral proteins~ transmembrane proteins Peripheral proteins~ surface of membrane Membrane carbohydrates ~ cell to cell recognition; oligosaccharides (cell markers); glycolipids; glycoproteins

Phospholipid Fluidity

Fluidic Nature of the Membrane To function properly: Lipids must be in a state of optimal fluidity Too much fluidity weakens the membrane -not enough cholesterol -too many unsaturated phospholipids Also, the membrane cannot be too rigid because transport through the membrane is inhibited Temperature changes can severely effect the membrane. HOW?

Mouse-Human Hybrid Cell (Pg. 108) David Frye & Micheal Edin (1970)

Freeze Fracture Method (Pg. 126)

Typical (integral)Transmembrane Protein

Proteins: Six Major Functions Observed- Pg. 128) C,D A G F G B

Lateral Transfer Across the Membrane See Pgs. 204-210 (Ch. 11- Cell Communication) Begins w/ signaling molecule called a Ligand Ligands-examples are hormones & proteins Involves several proteins: Receptor (1st messenger) binds w/the ligand Protein Kinases: an enzyme that transfers phosphate groups from ATP to a protein (uses ATP & move phosphates) G proteins & Adenylyl cyclase Cyclic AMP: 2nd messengers

Lateral Transfer of Information Across the Membrane Adenylyl Cyclase Ligand Enzymatic Rxns G Protein Receptor cAMP 2nd messenger Figure 5.13

Passive transport: Diffusion across a membrane In passive transport, substances diffuse through membranes without work by the cell They spread from areas of high concentration to areas of lower concentration Molecule of dye Membrane EQUILIBRIUM EQUILIBRIUM Figure 5.14A & B

Membrane Traffic - (Pg. 132) Diffusion~ tendency of molecules to move from areas of high concentration to areas of low. Concentration gradient Passive transport~ diffusion of a substance across a biological membrane Osmosis~ the diffusion of water across a selectively permeable membrane

Osmosis is the passive transport of water Hypotonic solution Hypertonic solution In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration Selectively permeable membrane Solute molecule HYPOTONIC SOLUTION HYPERTONIC SOLUTION Water molecule Selectively permeable membrane Solute molecule with cluster of water molecules NET FLOW OF WATER Figure 5.15

Two Models of Facilitated Diffusion http://www. wiley

Dialysis Tubing Experiment

Introductory Questions #4 Name the major molecules that make up the cell membrane. How thick is the membrane? How does the fluid mosaic model proposed by Singer & Nicholson (1972) compare with the Daveson & Danielli (1935) model? Briefly explain how the membrane remains fluidic in lower temperatures? What did the freeze fracture process and electron microscope reveal about the membrane? How does cholesterol act as a “buffer” for the membrane? How does a hypotonic solution differ from a hypertonic solution? What are the three forms of endocytosis? Explain how they are different.

Introductory Questions # What did the freeze fracture process and electron microscope reveal about the membrane? What purpose do protein Kinase enzymes serve in the signal transduction process? (Ch. 11 pgs. 204-210) How is diffusion different from facilitative diffusion? Name some factors that can affect diffusion rates of molecules. Name the ions used to show how active transport works in a the cell membrane. What role does ATP play during this process? What is the charge range difference across the membrane? Which side is positive and which side is negative?

Water balance between cells and their surroundings is crucial to organisms Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution The control of water balance (osmoregulation) is essential for organisms ISOTONIC SOLUTION HYPOTONIC SOLUTION HYPERTONIC SOLUTION ANIMAL CELL (1) Normal (2) Lysing (3) Shriveled Plasma membrane PLANT CELL Figure 5.16 (4) Flaccid (5) Turgid (6) Shriveled

An Artificial Cell Permeable to: monosaccharides & water Impermeable to: Disaccharides

Active Transport (Pg. 135)

Active transport in two solutes across a membrane FLUID OUTSIDE CELL Phosphorylated transport protein Active transport in two solutes across a membrane Transport protein First solute 1 First solute, inside cell, binds to protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell Second solute 4 Second solute binds to protein 5 Phosphate detaches from protein 6 Protein releases second solute into cell Figure 5.18

Common Type of Active Transport Utilizes ATP and a protein Moves substances against the concentration gradient (Low to High) Typical example is: Sodium-potassium pump (Observed in nerve cells)

Generating a Membrane Potential Membrane potential: a charge difference across the membrane Most commonly seen in nerve cells (sodium & potassium pump) – see pg 135 Achieved through actively pumping ions on one side of the membrane. (Na+ and K+) All cells have a potential with a slight negative charge on the inside a positive charge on the outside. Why???

Specialized Transport Transport proteins Facilitated diffusion~ passage of molecules and ions with transport proteins across a membrane down the concentration gradient Active transport~ movement of a substance against its concentration gradient with the help of cellular energy

Water Balance (pg. 133) Osmoregulation~ control of water balance Hypertonic~ higher concentration of solutes Hypotonic~ lower concentration of solutes Isotonic~ equal concentrations of solutes Cells with Walls: Turgid (very firm) Flaccid (limp) Plasmolysis~ plasma membrane pulls away from cell wall

Endocytosis vs. Exocytosis Endocytosis~ import of macromolecules by forming new vesicles with the plasma membrane •phagocytosis •pinocytosis •receptor-mediated Exocytosis~ secretion of macromolecules by the fusion of vesicles with the plasma membrane

Exocytosis and endocytosis transport large molecules To move large molecules or particles through a membrane a vesicle may fuse with the membrane and expel its contents (exocytosis) FLUID OUTSIDE CELL CYTOPLASM Figure 5.19A

or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

Three Types of Endocytosis

Material bound to receptor proteins Three kinds of endocytosis Pseudopod of amoeba Food being ingested Plasma membrane Material bound to receptor proteins PIT Cytoplasm Figure 5.19C

Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors Phospholipid outer layer LDL PARTICLE Receptor protein Protein Cholesterol Plasma membrane Vesicle CYTOPLASM Figure 5.20

The plasma membrane of an animal cell Glycoprotein Carbohydrate (of glycoprotein) Fibers of the extracellular matrix Glycolipid Phospholipid Cholesterol Microfilaments of the cytoskeleton Proteins CYTOPLASM Figure 5.12