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Cell Membranes

Cell Membranes. Standard Set 1 – Cell Biology 1c, 1e, 1a. Two Major Groups of Cells: Prokaryotic Cells Pro (before) karyotic (nucleus). No nucleus No membrane-bound organelles Most 1-10 microns in size Evolved 3.5 billion years ago Only bacteria.

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Cell Membranes

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  1. Cell Membranes Standard Set 1 – Cell Biology 1c, 1e, 1a

  2. Two Major Groups of Cells:Prokaryotic Cells Pro (before) karyotic (nucleus) • No nucleus • No membrane-bound organelles • Most 1-10 microns in size • Evolved 3.5 billion years ago • Only bacteria

  3. Two Major Groups of Cells:Eukaryotic Cells Eu (true) karyotic (nucleus) • Nucleus • Many organelles • From 100-1,000 microns in size • Evolved 1.5 billion years ago • All other cells

  4. Proteins are made by ribosomes on the roughER. Vesicles carry proteins from the roughER to the Golgiapparatus. Proteins are modified in the Golgiapparatus and enter new vesicles. Some vesicles release their proteins from the cell. Other vesicles remain in the cell and become lysosomes. An Internal Membrane System Processes Proteins

  5. In the library (ER) students (ribosomes) produce homework (proteins). Backpacks (vesicles) carry the homework (proteins) from the library (ER) to the teacher (Golgi apparatus). The teacher (Golgi apparatus) grades (modifies) the homework (proteins), which enters folders (new vesicles). Some folders (vesicles) release their homework (proteins) from the school (cell). Other folders (vesicles) remain in the school (cell). Understanding the Processing of Proteins

  6. Now….PLASMA MEMBRANE • Functions: • Helps cells maintain balance (homeostasis) • Provides flexible boundary between cell and environment • Controls flow of nutrients (glucose, amino acids, and lipids) • If cell needs more, nutrients OR ions flow in • If too much, nutrients OR ions flow out

  7. PLASMA MEMBRANE • Selective Permeability • A process in which plasma membrane allows some molecules to pass in while keeping others out. • Ex: Window Screen • Water: in and out freely • Sodium & Calcium ions: only at certain times, at certain amounts, through certain channels

  8. PLASMA MEMBRANE Plasma Membrane Oxygen Amino Acids Water Glucose Wastes Wastes Carbon Dioxide

  9. Cell Membranes Provide a Barrierthat separates the inside of a cell from the outside of a cell. • Cell membranes are not rigid, instead, they are fluid like a soap bubble. • Lipids create the fluid foundation of membranes by forming a “lipid bilayer”. • Cell membranes are selectively permeable, allowing only certain substances to leave and enter the cell.

  10. PLASMA MEMBRANE • Fluid Mosaic Model: model of plasma membrane • “Fluid”=Phospholipids move within membrane like water molecules in lake • Proteins in membrane move along phospholipids like boats • Proteins create mosaic pattern on membrane surface

  11. PLASMA MEMBRANE Phospholipid molecule Polar head (includes phosphate group) Nonpolar tails (fatty acids)

  12. PLASMA MEMBRANE • Proteins: • Recognition Proteins: • Serve as identification tags and cell surface attachment sites • Identifies cells to body’s immune system or blood type

  13. PLASMA MEMBRANE • Cholesterol: • Stabilizes phospholipids by preventing fatty acid tails from sticking together Cholesterol Molecule

  14. Plasma Membranes are made ofPhospholipids • Phospholipidsare fat molecules shaped like a head with two tails. • phospholipidshave a polar (water loving) region and a nonpolar (water hating) region. • phospholipidsautomatically form a bilayer when in water.

  15. Osmosisis simply the diffusion of water • Water molecules are attracted and “stick” to solute molecules. • This reduces the number of water molecules that can move freely on that side. • Water moves by osmosis from a greater to lesser concentration.

  16. Osmosiscreates three different osmotic conditions … • Hypotonic: The solute concentration in the environment is lower than in the cell. • Hypertonic: The solute concentration in the environment is higher than in the cell. • Isotonic: The solute concentration in the environment is equal to that in the cell.

  17. Examples of Osmosis in Nature ... • Animal cells burst (lysis) due to pressure on the plasma membrane when placed in a hypotonicsolution. • Animals cells shrivel (crenation) when water leaves the cell while in a hypertonicsolution.

  18. Examples of Osmosis in Nature ... • Plant cells are supported by turgor pressure within the vacuole when placed in a hypotonic solution. • Plant cells wilt when water leaves the vacuole due to plasmolysis when placed in a hypertonicsolution.

  19. Types of Cellular Transport • PassiveTransport:does not require energy to move across the cell membrane • ActiveTransport:requires energy to move across the membrane

  20. Diffusion • The movement of molecules from a region of higher concentration to a region of lower concentration through a selectively permeable membrane until an equilibrium is reached.

  21. PLASMA MEMBRANE • Proteins: • Transport Proteins: • Allows needed substances or waste materials to move through plasma membrane

  22. FacilitatedDiffusion • The movement of specific molecules from higher to lower concentration through a membrane byusing a channel protein.

  23. ActiveTransport Protein Pumps: Protein pumps require energy (ATP) and channel proteins to move ions (+/- charged particles) and large molecules (glucose) through a membrane against a concentration gradient. Example: Sodium-Potassium Pump

  24. Membrane Assisted Transport • Materials are placed inside of a membrane bubble called a “vesicle” • Exocytosis(exit): the dumping of waste materials outside of the cell by discharging them from waste vesicles. • Endocytosis(taking in): the engulfing of material by cells

  25. Let’s break it down… What about osmosis?

  26. Endocytosis: Cell surrounds and takes in material from environment • Material does not pass directly through membrane • Is engulfed and enclosed by portion of cell’s plasma membrane • Portion of membrane breaks away, leaving vacuole with contents which moves into cell

  27. TRANSPORT OF LARGE PARTICLES • Exocytosis: Expulsion/Release of large materials from cell • Used to excrete wastes • Also used to secrete hormones produced by cell

  28. The transport of large molecules into a cell is called what? The transport of large molecules out of a cell is called what?

  29. Assessment Quiz • Please take out a sheet of paper. • Use a pen. • Give your paper the proper heading. • Number your paper from 1 to 6.

  30. 1. What is this process? • Here water diffuses across selectively permeable membrane. Notice number of sugar molecules did not change on each side of membrane but number of water molecules did. What type of membrane?

  31. Osmosis: Diffusion of water across a selectively permeable membrane • Regulating water flow through the plasma membrane is important factor in maintaining homeostasis.

  32. 2. What kind of solution is this? • Concentration of dissolved substances in the environment is same as concentration of dissolved substances inside cell. • Water molecules move into and out of cell at same rate • Cells maintain normal shape isotonic

  33. CELLULAR TRANSPORT: OSMOSIS

  34. 3. What is this process? • Carrier proteins pick up ions or molecules near cell membrane and carry them across membrane releasing them on other side. • Energy is expended by proteins.

  35. ACTIVE TRANSPORT • Movement of materials through membrane against concentration gradient • From lower concentration to higher • Requires energy • Sodium-Potassium Pump: • Special transport protein in plasma membrane of animal cells that transports sodium out of the cell and potassium into the cell against their concentration gradients. • Ions pumped and generate voltage across membrane • Allows for body to transmit electrical impulses

  36. 4. What is this process called? • Materials pass through the plasma membrane with concentration gradient • Requires the cell to use no energy

  37. Simple Diffusion • Simple Diffusion through Plasma Membrane with concentration gradient • Requires the cell to use noenergy • Free Movement of particles across membrane of cell = passive transport

  38. 6. What is this transport process called? • Transport proteins help materials move through plasma membrane • Materials move with the concentration gradient • No energy is expended by the cell Facilitated Diffusion

  39. ` 8. In what kind of solution does water leave a cell by osmosis, causing cell to shrink and lose its water? Hypertonic

  40. 9. What is this process called? • Cell surrounds and takes in material from environment • Material does not pass directly through membrane • Is engulfed and enclosed by portion of cell’s plasma membrane • Portion of membrane breaks away, leaving vacuole with contents which moves into cell Endocytosis

  41. 10. Please give it a try…

  42. Where does endocytosis fit and where does exocytosis fit in the sentence below?Please copy and complete. • Some unicellular organisms ingest food by ____________and release wastes or cell products from a vacuole by ___________.

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