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The Cell Membrane

The Cell Membrane. Structure and Function. Cell Membrane Functions. C ell membrane surrounds the cell, regulating the transport of materials into and out of the cell. Cell Membrane Structure. Lipid Bilayer: a double layer of phospholipids that make up the cell membrane. Phospholipid.

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The Cell Membrane

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  1. The Cell Membrane Structure and Function

  2. Cell Membrane Functions • Cell membrane surrounds the cell, regulating the transport of materials into and out of the cell

  3. Cell Membrane Structure • Lipid Bilayer: a double layer of phospholipids that make up the cell membrane

  4. Phospholipid • Phosphate Head: • Polar • Hydrophilic (attracted to water) • Two Fatty Acid Tails: • Nonpolar • Hydrophobic (avoids water) • Two Layers • Outsides: Polar Heads • Inside: Nonpolar Tails

  5. Other lipids ? • Lipids • Fatty acids • Fats and waxes • Steroids • Cholesterol • Testosterone • Phospholipids

  6. Cell Membrane Structure • Phospholipids are arranged so hydrophilic (water loving) ends face outside and hydrophobic (water fearing) tails create the interior

  7. Cell Membrane Structure • Phospholipid Bilayer • Transmembrane Proteins • Cholesterol (a steroid) • Glycoprotein and Carbohydrate

  8. Cell Membrane Structure • Transmembrane Proteins • Job: • Attachment point for one cell to attach to a neighbor • Anchor cell in place • Create channels for large and/or polar molecules to pass

  9. Cell Membrane Structure • Cholesterol • Job: • Maintains fluidity of cell membrane

  10. Cell Membrane Structure • Glycolipids and Carbohydrates • Job: • Serve as cell markers for identification

  11. Cell Membrane Structure • The Fluid Mosaic Model • The membrane is dynamic – molecules are constantly moving • Video Link

  12. Selectively Permeable • The cell membrane is selectively permeable, meaning some substances can pass through the cell membrane, but others can’t! • “Permeable” is the ability for something to pass through

  13. Passive Transport Osmosis and Diffusion

  14. Selectively Permeable • The cell may transport substances • Passive Transport: No Energy required • Active Transport: Uses energy (ATP)

  15. Passive Transport • Movement of a substance into/out of a cell without using energy • HIGH  LOW concentration • 3 Types • Simple Diffusion • Facilitated Diffusion • Osmosis

  16. About Concentration… • We just learned that substances move from HIGHLOW concentration in passive transport…but what do we mean by concentration? • Means amount dissolved in a container • How do you like your sweet tea? a. Unsweet (low concentration of sugar) b. Sweet c. Super sweet(high concentration of sugar) • Solute = Substance dissolvedin water

  17. Concentration Gradients • A concentration gradient is the difference in the concentration, or amount, of something in a space • In the box below, the dots have a higher concentration on the left than the right, so they begin movement to the right • When the concentration gradient is the same throughout the area, it is ina dynamic equilibrium • Particles are moving from one side to the other, but at the same rate. Picture: www.hartnell.edu

  18. Passive Transport: Diffusion • Diffusion is when a substance moves from an area of high concentration to low concentrationarea • Diffusion will continue until balanced/equal “at equilibrium” • In this case, small, nonpolar particles cross through the membrane • Food Coloring Demo!

  19. Facilitated Diffusion • Large molecules require special protein channelsto move through • Ex. Ions, glucose • Video Link

  20. Passive Transport: Osmosis • Osmosisis the diffusion of water across a selectively permeable membrane • Water moves from an area of high concentration (lots of water) to low concentration (little water) • Passive Transport: • Water moves with its concentration gradient • No energy is required Picture: scienceaid.co.uk

  21. About Osmosis • Water can move into or out of the cell, depending on the environment (solution) that the cell is in • Solvent + Solute = Solution • Solvent does the dissolving (ex. Water) • Solute substance dissolved(ex. Salt)

  22. Describing Solutions

  23. How Osmosis Works

  24. Osmosis • Onion in Salt Water • Blood Cells • Take a look at the raisins on your desk…what’s happening? Same Swelling Shrinking Picture: www.peoi.org

  25. Isotonic, Hypotonic, or Hypertonic? 10% NaCL Environment 90 % H2O CELL 10% NaCL 90 % H2O

  26. Water Goes? • Isotonic-Water goes in/out (balanced); cell stays the same! 10% NaCL Environment 90 % H2O CELL 10% NaCL 90 % H2O

  27. Isotonic, Hypotonic, or Hypertonic? 10% NaCL Environment 90 % H2O CELL 20% NaCL 80 % H2O

  28. Water Goes? • Hypotonic-water goes IN! Cell swells! 10% NaCL Environment 90 % H2O CELL 20% NaCL 80 % H2O

  29. Isotonic, Hypotonic, or Hypertonic? 10% NaCL Environment CELL 5% NaCL

  30. Water Goes? • Hypertonic-water goes OUT-Cell Shrinks!! 10% NaCL Environment Often, you will just be given the solute concentration in the environment. What is the water concentration? Would it move in or out? CELL 5% NaCL

  31. Bellringer 30% solute • Identify the solution as iso, hyper, or hypotonic and draw arrows labeling the direction of water movement. • A cell is placed into a salt solution. The salt concentration is greater in the solution than inside the cell. Which describes what will most likely happen? • Water will flow into the cell by active transport • Water will flow into the cell by passive transport • Water will flow out of the cell by active transport • Water will flow out of the cell by passive transport 70% H2O 80% H2O 20 % solute 40% solute 85% H2O 15% solute 70% H2O

  32. Active Transport Movement Requiring Energy

  33. Active Transport • Molecules move across the membrane AGAINST their concentration gradient • Moving LOW to HIGH • ENERGY is required! (imagine trying to push your way through a crowd vs. going with the flow…) • Two Types • Protein Pumps • Bulk Transport

  34. Protein Pumps • Transport small molecules/ions AGAINST their concentration gradients • (LOW HIGH) • Uses ATP (cell energy) Notice the ATP

  35. Bulk Transport • Larger molecules (proteins, starch) are transported by vesicles that merge with the cell membrane • Exocytosis-contents leaving the cell through the membrane • Endocytosis-contents entering in vesicles (pinocytosis and phagocytosis)

  36. Homeostasis Maintaining Balance

  37. Homeostasis • The process by which an organism’s internal environment is kept in equilibrium (stable) in spite of changes in the external environment • Examples: • Internal Temperature • Sweating removes excess body heat • Shivering increases heat production • Water balance • Kidneys adjust water amount in urine • A physical response to stress • Breathing/heart rate increases • Pupils dilate • Sweating)

  38. Homeostasis • Homeostasis requires energy • For active transport to deliver needed molecules • T0 rid cell of toxins • To move to avoid danger or find food

  39. Homeostasis in Cells Cells can maintain homeostasis in a number of ways… • Controlling substances that cross the membrane • Active and Passive transport)

  40. Homeostasis in Cells Cells can maintain homeostasis in a number of ways… • Buffers • Cells produce buffers to help maintain a constant pH. • Examples: • Human blood cells must maintain a pH of 7.35-7.45 • Cells in stomach maintain a pH of 3 • Cells in Small Intestine maintain a pH of 6 • What is a buffer? • A chemical that can raise or lower the pH(it can behave like an acid or a base)

  41. Homeostasis Maintenance of homeostasis is vital for life! https://www.youtube.com/watch?v=6fhbbFd4icY

  42. If energy is needed to move materials into or out of a cell, what is most likely occurring? • Active transport • Passive transport • Osmosis • Diffusion • During strenuous exercise, the body temperature increases. The body responds to the increase in temperature by sweating, which helps to reduce the body temperature. Which is demonstrated in this situation? • Excretion • Metabolism • Homeostasis • Synthesis

  43. Which of the following serves as the cell’s boundary from its environment? • Mitochondria • Cell membrane • Chloroplast • Channel protein

  44. Which of the following is a function of the cell membrane? • Breaks down lipids, carbohydrates, and proteins in the body • Stores water, salt, proteins, and carbohydrates • Keeps the cell wall in place • Regulates which materials enter and leave the cell

  45. The cell membrane contains channels and pumps that help move materials from one side to the other. What are these channels and pumps made of? • Carbohydrates • Lipids • Bilipids • Proteins

  46. Diffusion is the movement of molecules from: • An area of low concentration to an area of high concentration • An area of high concentration to an area of low concentration • An area of equilibrium to an area of high concentration • All of the above

  47. Diffusion occurs because: • Molecules constantly move and collide with each other • The concentration of a solution is never the same throughout a solution • The concentration of a solution is always the same throughout a solution • Molecules never move or collide with each other

  48. When the concentration of molecules on both sides of the membrane is the same, the molecules will: • Move across the membrane to the outside of the cell • Stop moving across the membrane • Move across the membrane in both directions • Move across the membrane to the inside of the cell

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