Slide 1 / 181 Slide 2 / 181 AP BIOLOGY Membranes & Proteins Slide 3 / 181 Membranes & Proteins Click on the topic to go to that section · Cell Membranes · Transport Proteins · Signaling Proteins · Enzymatic Proteins
Slide 4 / 181 Cell Membranes Return to Table of Contents Slide 5 / 181 Biological Membranes The term membrane most commonly refers to a thin, film-like structure that separates two fluids. Membranes act as a container for biological systems, surrounding protobionts, cells, and organelles. The video below shows experiments done at a laboratory in France to study the properties of lipids. The only substances used in the making of this video are lipids, water and dye . The lipids and dye were mixed and then injected into aqueous solution. Try to figure out some of the properties that make lipids useful as membranes by watching the video. Click here for the video Slide 6 / 181 Phospholipids The most important lipid that composes the majority of biological membranes is the phospholipid . The amphiphilic nature of these lipids cause them to naturally form a spherical bilayer.
Slide 7 / 181 Lipids and the Membrane Phospholipids form two parallel lines with their hydrophobic ends in between. The hydrophobic ends are protected from the water by the hydrophilic ends, creating a bilayer. In animals, cholesterol inserts itself into the membrane in the same orientation as the phospholipid. Cholesterol immobilizes the first few hydrocarbons in the phospholipid, making the bilayer more stable, and impenetrable to water molecules. Slide 8 / 181 Selective Permeability Membranes act as selectively permeable barriers, allowing some particles or chemicals to pass through, but not others. The properties of the phospholipid bilayer dictate what can pass through a membrane. Slide 9 / 181 Selective Permeability When phospholipids come together, they create a wall that is tightly packed with a core that is nonpolar. However, the individual molecules are not fixed and small gaps form as they fluidly move around in the membrane.
Slide 10 / 181 Selective Permeability So what molecules CAN pass through a membrane made of just phospholipids? Slide 11 / 181 1 Will O 2 pass through? Yes No Why? Slide 12 / 181 2 Will H 2 O pass through? Yes No Why?
Slide 13 / 181 3 Will Na + pass through? Yes No Why? Slide 14 / 181 4 Will C 6 H 12 O 6 pass through? Yes No Why? Slide 15 / 181 Selective Permeability To recap... Large molecules or charged molecules will not make it through a lipid bilayer. Some examples: sugars, ions, nucleic acids, proteins
Slide 16 / 181 How do cells get what they need? We know that cell membranes are made of lipid bilayers, and we know that cells require things like sugar and nucleic acids and proteins and sodium that can't pass through this barrier. So how do cells get the materials they need? Slide 17 / 181 Fluid Mosaic Proteins embedded in the cell membrane facilitate the movement of large or charged molecules through the barrier. By doing this, the internal chemistry of the cell becomes far different than its surroundings. The pattern of lipids and proteins in the cell membrane is referred to as the fluid mosaic model. Slide 18 / 181 Proteins Regulate What is in a Cell Proteins are long chains of amino acids that fold up on each other to form useful structures in biological systems. Below is a ribbon diagram of an amino acid chain that forms a channel protein.
Slide 19 / 181 Types of Membrane Proteins Peripheral proteins stay on only one side of the membrane. Integral proteins pass through the hydrophobic core and often span the membrane from one end to the other . Proteins in the plasma membrane can drift within the bilayer. They are much larger than lipids and move more slowly throughout the fluid mosaic. Slide 20 / 181 Carbohydrates and the Membrane Glycoproteins have a Glycolipids are lipids with carbohydrate attached to a a carbohydrate attached. protein and serve as points Their purpose is to provide of attachment for other energy and to act in cells, bacteria, hormones, cellular recognition. and many other molecules. protein Slide 21 / 181 Proteins Regulate What is in a Cell An integral protein forms a pore that allows specific substances to diffuse across the membrane, even if they are large or have charge.
Slide 22 / 181 Review Membrane Transport Watch this video to review the way in which membranes can regulate by transport. Click here for a review of solute moving through membranes If further review is needed please see NJCTL's first year biology course. Membranes First Year Course Slide 23 / 181 5 When diffusion has occurred until there is no longer a concentration gradient, then _______________ has been reached. A equilibrium B selective permeability C phospholipid bilayer D homeostasis Slide 24 / 181 6 In osmosis, water molecules diffuse from A inside the plasma membrane to outside only B outside the plasma membrane to inside only from areas of high solute concentration to areas of low C solute concentration from areas of low solute concentration to areas of D high solute concentration
Slide 25 / 181 7 What type of environment has a higher concentration of solutes outside the plasma membrane than inside the plasma membrane? A hypertonic B isotonic C normal D hypotonic Slide 26 / 181 8 What type of solution has a greater flow of water to the inside of the plasma membrane? A hypertonic B isotonic C normal D hypotonic Slide 27 / 181 9 A red blood cell will lyse when placed in which of the following kinds of solution? hypertonic A hypotonic B isotonic C any of these D
Slide 28 / 181 10 Dialysis tubing is permeable to monosaccharides only. Which solute(s) will exhibit a net diffusion out of the cell? A sucrose environment B glucose 0.01M sucrose 0.01M glucose Cell: 0.01M fructose 0.05M sucrose C fructose 0.02M glucose D sucrose, glucose, and fructose E sucrose and glucose Slide 29 / 181 11 Is the solution outside the cell isotonic, hypotonic, or hypertonic? A Hypertonic environment 0.01M sucrose 0.01M glucose B Hypotonic Cell: 0.01M fructose 0.05M sucrose 0.02M glucose C Isotonic Slide 30 / 181 12 The process by which a cell ingests large solid particles, therefore it is known as "cell eating". A Pinocytosis B Phagocytosis C Exocytosis D Osmoregulation
Slide 31 / 181 13 Antibodies are embedded in cell membranes and bind to antigens on the surface of foreign cells. What type of molecule is an antibody? phospholipid A glycolipid B glycoprotein C enzyme D Slide 32 / 181 Osmosis In animal cells, water moves from areas of low solute concentration to areas of high solute concentration during osmosis. In plants, bacteria, and fungi, however, the cell wall exerts a force on the internal environment of the cell and affects the net flow of water through the cell membrane. The effects of solute concentration and the pressure provided by the cell wall are incorporated into a quantity called water potential ( ). Osmosis moves water from areas of high water potential to areas of low water potential. Slide 33 / 181 Water Potential Water potential is calculated using the following equation: Water potential is measured in megapascals (MPa) or bar. 1 MPa = 10 bar Note: Animal cells do not have cell walls so pressure potential = zero
Slide 34 / 181 14 An animal cell with a solute potential of -0.30 MPa (megapascals) is placed in a sucrose solution with a solute potential of -0.55 MPa. What is the net direction of osmosis? A into the cell B out of the cell C not enough information Slide 35 / 181 15 A fungal cell with a solute potential of -2.5 bar is place in a saline solution with a potential of -1.2 bar. What is the net direction of osmosis? A into the cell B out of the cell C not enough information Slide 36 / 181 16 In a given plant cell, the cell wall exerts 2.3 bar of pressure and the solute potential is -3.0 bar. Calculate the water potential.
Slide 37 / 181 17 In a given animal cell, the solute potential is -0.25 MPa. Calculate the water potential. Slide 38 / 181 18 A turgid plant cell with a solute potential of -7.0 bar is placed in pure water. When the cell reaches osmotic equilibrium with its surroundings, what is the pressure potential of the cell? Slide 39 / 181 19 A bacterial cell with a solute potential of -9.0 bar is placed in a sucrose solution with a solute potential of -4.0 bar. No net movement of water occurs. What is the pressure potential of the cell?
Slide 40 / 181 Solute Potential Solute potential is dependent upon type and concentration of solute. Its value can be determine using the following equation: = -iCRT s i =# of particles/ions in one molecule of solute after dissociation C = molar concentration (M) R = pressure constant (0.0831 L bar/mol K or 0.0083 L MPa/mol K) T = temperature (K) Slide 41 / 181 20 What does i equal for NaCl? = -iCRT s Slide 42 / 181 21 What does i equal for fructose? = -iCRT s
Slide 43 / 181 22 What does T equal for a solution at 26 0 C? = -iCRT s Slide 44 / 181 Slide 45 / 181 23 Calculate water potential (in bar) for a cell that contains 0.9M NaCl and is stored at 19 o C.
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