1 The Cell Membrane & Movement of Materials In & Out of Cells PACKET #11
Introduction I 2 Biological membranes are phospholipid bilayers with associated proteins. Current data support a fluid mosaic model of the cell membrane. In 1935, Davson and Daniella stated that phospholipids form a membrane two molecules thick. Singer and Nicholson developed the fluid mosaic model in 1972. Furthermore, the membrane is only 10nm thick.
Introduction II 3 Biological membranes fuse and form closed vesicles. Endocytosis and exocytosis are products of membrane fusion. More later.
Cell Membrane 4
Properties of Phospholipids 5
Phospholipids are Amphipathic 6 Molecules with both hydrophilic and hydrophobic properties are termed amphipathic Other examples Sterols Cholesterol Glycolipids Hydrophilic (sugar) head The aqueous environment inside and outside the cell prevent membrane lipids from escaping the bilayer
Fluidity of the Membrane 7 Depends on Two Main Features Saturated vs. Unsaturated Fatty Acid tails (phopsholipids) Unsaturated more fluid Cholesterol Kinks prevent molecules from packing together Absent in plants, yeast and bacteria Fill the holes produced by kinks Stiffens bilayer and makes it less fluid and permeable.
Fluidity of the Cell Membrane II 8
Check Point 1 9 LEARNING GOALS 4 In addition to level 3, Describe the relationship between the cell membrane, homeostasis and sweating (Packet #9). STUDENT EVIDENCE {Student developed Questions} 3 The student will (target learning goal) Identify and describe the basic unit of the cell membrane (phospholipid). Explain how the relation of phospholipids to water. 2 The student will understand/perform basic processes, such as: Relate the structure phospholipids to water (a polar molecule). Identify reactants, products, and basic functions of photosynthesis, anaerobic, and aerobic cellular respiration. The student will recognize or recall specific vocabulary, such as: Phospholipid; hydrophilic; hydrophobic; amphipathic; saturated; unsaturated 1 With help, I have a partial understanding of some of the simpler details and processes at level 2. I can describe the basic structure of the cell membrane.
Proteins of the Cell Membrane 10
Functions of Membrane Proteins 11 Cell Membrane Proteins Six different functions Functions of Proteins Transport Enzyme Activity Signal Transduction Cell to cell Recognition Intercellular Joining Attachment to Cytoskeleton
Integral vs. Peripheral Proteins 12 Integral Proteins A protein that is firmly anchored in the plasma membrane via interactions between its hydrophobic domains and the membrane phospholipids Directly attached to the membrane
Integral vs. Peripheral Proteins 13 Peripheral Proteins Not embedded in the lipid bilayer Can be released from the membrane by relatively gentle extraction procedures Possible key player in cell communication.
Transmembrane Protein 14 Protein that spans the entire membrane Have both hydrophobic and hydrophilic regions Alpha helical secondary structure is normally the hydrophobic regions of the protein
Check Point 2 15 LEARNING GOALS 4 In addition to level 3, Describe the relationship between proteins of the cell membrane, classes of proteins and enzymes (Packet #6 & 7). STUDENT EVIDENCE {Student developed Questions} 3 The student will (target learning goal) Explain the roles of proteins within the cell membrane 2 The student will understand/perform basic processes, such as: Describe the functions of proteins within the cell membrane The student will recognize or recall specific vocabulary, such as: Integral protein; Peripheral protein 1 With help, I have a partial understanding of some of the simpler details and processes at level 2. I can list the types of proteins within the cell membrane.
16 Diffusion
Introduction 17 Atoms and molecules, above absolute zero, exhibit motion. This random motion allows particles to move from an area of higher concentration to an area of lower concentration in an attempt to reach equilibrium.
Introduction 18 There are 5 ways of transporting materials across the cell membrane Diffusion Regular & Facilitated Passive Transport Active transport Osmosis Phagocytosis Pinocytosis
Categories of Diffusion I 19 Regular Diffusion Movement of molecules down the concentration gradient High to low Facilitated Diffusion Movement of molecules down the concentration gradient via a channel Passive Transport Active Transport Regular Diffusion Facilitated Diffusion In cells, these channels are found in proteins Categories of Diffusion Osmosis Special type of diffusion More to come later Phagocytosis Active transport Movement of molecules against the concentration gradient via channels and with the use of energy. Pinocytosis Low to high
Diffusion 20
Diffusion 21 The movement of a substance from an area of high concentration to an area of low concentration The difference in concentration between the two regions is known as the concentration gradient
Rate of Diffusion 22 The rate of diffusion depends on The difference in concentration The greater the concentration gradient, the faster the process The distance between the two regions Smaller distance means faster process The area If the total area is increased, the faster the process The size of the molecules Small and fat-soluble molecules will diffuse faster
Passive Transport Regular vs. Facilitated Diffusion 23 Regular Diffusion Movement of molecules is from high concentration to low concentration No proteins are used No energy (ATP) is required Facilitated Diffusion Movement of molecules is from high concentration to low concentration Proteins are used No energy (ATP) is required
Active Transport 24 Materials are moved against the concentration gradient Molecules move from an area of low concentration to an area of high concentration Proteins are used to move materials across the membrane Energy is also used.
Active Transport II 25 Cells carry our active transport in three ways ATP driven pumps Active Transport Couple uphill transport with hydrolysis of ATP Coupled transport (co-transport)* ATP Pumps Co- Transport Light Driven Pumps Light driven pumps Found mainly in bacterial cells Bacteria Cells Input of energy from light Bacteriohodopsin
Active Transport ATP DRIVEN PUMPS 26
Active Transport ATP Driven Pumps 27 Energy is used Because energy is used, cells carrying out active transport have A high respiratory rate Many mitochondria A high concentration/reserve of ATP Any factor which reduces or stops cell respiration will stop active transport Cyanide
Co-Transport INVOLVES ACTIVE TRANSPORT 28
Co-Transport I The Active Transport of H + ions 29 Hydrogen gradients are used to drive membrane transport in plants, fungi and bacteria These are not sodium-potassium pumps
Co-Transport II The Active Transport of H + ions II 30 Hydrogen pumps, found in the plasma membrane, pump H + out of the cell This can also be described as primary active transport Setting up an electrochemical gradient
Co-Transport III 31 Pump creates an acidic ph in the medium surrounding the cell H + re-enters the cell via a cotransporter Usually transports a substance in addition to the H + The uptake of sugars and amino acids, into bacterial cells for example, are driven by the presence H + pumps
Active Transport Light Driven Pumps H + Pumps in Bacteria 32
Active Transport Light Driven Pumps H + Pumps in Bacteria 33 In some photosynthetic bacteria, the H + gradient is created by the activity of light driven H + pumps such as bacteriorhodopsin. In plants and fungi and many other bacteria, the gradient is set up by ATPases in their plasma membrane
34 Types of Ports
Types of Ports 35
Review so far 36 Movement of Materials in/out of Cells Passive Transport Active Transport Regular Diffusion Facilitated Diffusion
Sodium Potassium Pump 37
Electrogenic Pump 38 These pumps are used to move electrically charged molecules Small organic or inorganic ions MOST cell membranes have a voltage across them and results in a difference in electric potential on each side i.e. the membrane potential.
Electrogenic Pump 39 The membrane potential exerts a force on any molecule that carries an electrical charge Cytoplasmic side is USUALLY at a negative potential relative to the outside This tends to pull positively charged solutes into the cell and drive negative charged ones outside the cell Net driving force = electrochemical gradient
The Sodium Potassium Pump 40 For some, ions, voltage and concentration gradients work in the same direction Sodium Potassium Pump
Movement of Glucose PUTTING IT ALL TOGETHER 41
The Movement of Glucose 42 The Na + gradient generated by the sodium-potassium pump can be used to drive active transport of a 2 nd molecule. The downhill movement of the first solute down provides the energy to drive the uphill transport of the second.
Check Point #3 43 LEARNING GOALS 4 In addition to level 3, Describe the relationship between co-transport, the cell, the pancreas, blood glucose levels and diabetes. STUDENT EVIDENCE {Student developed Questions} 3 The student will (target learning goal) Describe how glucose is moved in and out of cells with the help of the sodium potassium pump. 2 The student will understand/perform basic processes, such as: Students will understand the different types of diffusion. The student will recognize or recall specific vocabulary, such as: Random motion; equilibrium; diffusion; facilitated diffusion; active transport; cotransport; sodium-potassium pump 1 With help, I have a partial understanding of some of the simpler details and processes at level 2. I can list the ways materials are transported across the cell membrane.
44 Osmosis SPECIAL CASE OF DIFFUSION
Osmosis 45 Concise Definition The diffusion of water (liquid solvent) across a selectively permeable membrane Detailed Definition Transfer of a liquid solvent through a semi permeable membrane, that does not allow dissolved solids (solutes) to pass from an area of high concentration to an area of low concentration
46 Osmotic Pressure, Osmotic Potential & Solute Potential
Osmotic Pressure 47 Osmotic Pressure Is a measure of the tendency of water to move INTO a solution. The driving force for the water and is the difference in water pressure on both sides of the membrane. The differences in pressure provides a net pressure that is exerted by the flow of water as it moves through the semi-permeable membrane. Class Illustration
Osmotic Potential = Osmotic Pressure 48 Osmotic Potential Difference in osmotic pressure that draws water from an area of less osmotic pressure to an area of greater osmotic pressure. The potential of a solution to pull in water Value is always negative The more concentrated the solution, the more negative its osmotic potential
Osmotic Potential = Osmotic Pressure = Solute Potential 49 The presence of solutes, in the solutions, impact the direction of the movement of water. The ability of a solution to pull in water depends on the number of solute particles present. The higher the amount of solutes in the solution, the lower the solute potential. The solution is more concentrated. Remember, from previous slide, the value is always suppose to be negative.
Osmotic Potential = Osmotic Pressure = Solute Potential 50 All three terms represent a measure of the ability of a solution to pull in water. The value is always negative. The more solutes present, the more negative the value. Represented by s
Osmotic Potential = Osmotic Pressure = Solute Potential 51 When two solutions have the same osmotic potential, they are said to be isotonic. Where one solution has a greater osmotic potential compared to the other, it is described as being hypertonic. i.e. It is more concentrated. The solution with the lower osmotic potential is described as being hypotonic. Less concentrated.
Pressure Potential 52 Solutions/Water are also under the influence of external pressures. These external pressures are measure as pressure potential. This force (pressure) is not the same as the one caused by the movement of the liquid solvent (water). Represented by p Negative or positive depending on conditions.
Water Potential 53 Measure of the tendency of water to leave a solution. Combination of the sum of osmotic potential/solute potential and pressure potential. = s + p
Water Potential II 54 When measuring the water potential of two solutions, the solution with the lower water potential receives water from the solution with higher water potential Osmosis!
55 Cells and Osmosis
Pressure Potential in Plant Cells 56 In plant cells, the cell contents press the plasma membrane against the cell wall producing an external force called turgor pressure. Results in a turgid plant cell Pressure potential is positive
Pressure Potential in Plant Cells II 57 Special plant cells that make up xylem, tissue that conducts water in plants, undergoes transpiration. This transpiration results in a negative pressure potential.
Cells & Osmosis 58
Cells & Osmosis 59
Check Point #4 60 LEARNING GOALS 4 In addition to level 3, Describe the relationship between osmosis, the cell, the kidneys, urination and dehydration. STUDENT EVIDENCE {Student developed Questions} 3 The student will (target learning goal) Explain why water can enter and leave cells. 2 The student will understand/perform basic processes, such as: Identify osmotic pressure, osmotic potential and solute potential The student will recognize or recall specific vocabulary, such as: Osmosis; osmotic pressure; osmotic potential; solute potential 1 With help, I have a partial understanding of some of the simpler details and processes at level 2. I can define osmosis.
Phagocytosis, Pinocytosis, Endocytosis and Exocytosis 61
Phagocytosis 62 The take up of large particles by cells via vesicles formed in the plasma membrane The cell invaginates to form a depression in which particles are contained This then pinches off to form a vacuole White blood cells Neutrophils Monocytes
Pinocytosis 63 The take up of liquids rather than solids Vacuoles are smaller than those used during phagocytosis
Endocytosis vs. Exocytosis 64 Both phagocytosis and pinocytosis involve the taking of materials into the cell in bulk. These are examples of endocytosis The removal of materials from the cell in bulk is called exocytosis.
Check Point #5 65 LEARNING GOALS 4 In addition to level 3, Describe the relationship between the immune system, the body fighting pathogens and phagocytosis/endocytosis. STUDENT EVIDENCE {Student developed Questions} 3 The student will (target learning goal) Explain and describe the process in which cells can absorb materials in bulk. 2 The student will understand/perform basic processes, such as: Identify ways that cells can absorb (take in) larger substances in bulk. The student will recognize or recall specific vocabulary, such as: Phagocytosis; pinocytosis; endocytosis; exocytosis 1 With help, I have a partial understanding of some of the simpler details and processes at level 2. I can describe how cells take up larger molecules.
66 Review