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Understanding Cell Membranes: Structure, Function, and Transport

Explore the cell membrane's phospholipid bilayer, monomers of fatty acids, and the fluid mosaic model. Learn about diffusion, osmosis, and factors affecting transport rates. Understand the concepts of hypotonic, hypertonic, and isotonic solutions and their effects on cells. Delve into facilitated transport, active transport, and cell processes like endocytosis and exocytosis. This comprehensive review provides insights into the complex mechanisms involved in cellular transport and membrane functions.

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Understanding Cell Membranes: Structure, Function, and Transport

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  1. Cell Membrane

  2. Review of phospholipid bilayer

  3. Monomers of fatty acids are used to build triacyglycerol (fats) and membrane lipids 3:12

  4. Hydrophobic effect 2:20

  5. A lipid bilayer prevents the diffusion of polar substances solutes spontaneously diffuse from a region of high concentration to a region of low concentration a lipid bilayer prevents the of polar substances of the inner compartment (also prevents the inward diffusion of polar substances) 3:13

  6. Cell Membrane – fluid mosaic model Composed of: • Lipids • double layer – • Proteins • surface • embedded proteins • Act as • Act as • Carbohydrates • Attached to surface on lipids or proteins • Many act as cards

  7. Cell Membrane • The cell membrane is permeable • Materials may cross the cell membrane in 3 methods: • through the membrane • Diffusion (passive transport) • Openings created via • Diffusion via channel (e.g. osmosis) • Diffusion via carrier (facilitated transport) • Carrier (active transport) • the cell membrane • Exocytosis or endocytosis (active transport)

  8. Cell Membrane is Selectively Permeable

  9. Transport of Molecules via Diffusion

  10. Factors effecting diffusion rate • gradient • of solute molecule • of medium (solvent) • Solubility of molecule (polarity/charge) • Temperature of • stream (continuous movement of cytoplasm moves molecules around the cell)

  11. Diffusion across a cell membrane • Diffusion: the of molecules from an area of concentration to an area of concentration until distributed • Diffusion is most rapid when there is a different in concentration (this is called the concentration gradient) • As the concentration decreases, the rate of diffusion • The rate of diffusion also depends on molecule and ; and the temperature and of the .

  12. Diffusion across a cell membrane

  13. Osmosis • Diffusion of H2O across a selectively permeable membrane • Every solution is made up of and the • Solute – the substance being • Solvent – the liquid that the is being dissolved within

  14. Osmosis • The of water across a cell membrane depends on the type of solution (the solute of the solution) on both sides of the barrier • The tonicity ( ) of a cell can be classified by the following : • Hypotonic – a solution with a solute concentration (and so more H2O ) compared to the other solution. • Hypertonic – The solution that has a solute concentration (and so less H2O ) compared the other solution • Isotonic – the solutions have H2O concentration

  15. Cells in Hypertonic Solutions • In hypertonic solutions, the of solute molecules the cell is higher than the concentration the cell • As a result, water out of the cell until equilibrium is • Cells in hypertonic solutions usually because the cells activities are by lack of • Scientific term when RBC shrinks is crenation

  16. Cells in Hypotonic Solutions • In a solution, the concentration of solute molecules the cell is lower than the of solutes inside the cell • Water will therefore flow into the until equilibrium is established • The flow of water into a cell causes it to • Scientific term when water enters the RBC is hemolysis

  17. Cells in Isotonic Solutions • In an isotonic solution, the concentration of solutes outside of the cell are • Water will therefore into and out of the cell at equal rates; there will be no movement of water

  18. Movement of Water *WATER WILL ALWAYS FLOW FROM HYPOTONIC TO A HYPERTONIC SOLUTION*

  19. : increase in vacuole's volume causes the cell membrane to push against the cell wall

  20. Transport of Molecules by Carriers

  21. Facilitated Transport • Follows the gradient, so therefore, it is a passive transport

  22. Facilitated Transport • Doesn’t require • Transports large molecules and charged ions since they cannot freely diffuse across the hydrophobic cell . • Carrier protein ( ) molecule in membrane is gated • CP molecule to be • CP to the molecule being • CP a conformational change and its gate opens and releases molecule to the other side • moves across the cell membrane in this manner

  23. Conformational Change in Proteins

  24. Active Transport • Requires energy since molecules move against the concentration gradient • Carrier protein molecule in membrane is gated • CP molecule to be transported • CP to the molecule being transported • ATP CP to open its gate to release the molecule to the side • Example: pump

  25. Sodium-Potassium Pump

  26. Endocytosis and Exocytosis

  27. Endocytosis • Is an process and energy • Other molecules which can’t cross the cell membrane through protein channels or carriers due to their size/type enter the cell via • During endocytosis, the membrane off the cell membrane and smaller vesicle is made, which carries the material being transported in • Two types on endocytosis:

  28. Phagocytosis • This type of is used by the immune system cells • Large or bacteria cells are engulfed by cell membrane • Fused with to break the bacteria down

  29. Pinocytosis • Other large taken in by the cell • Also known as “ ”

  30. Exocytosis • Getting rid of from the cytoplasm to the exterior of the cell • Membrane of the fuses with the cell membrane and discharges its

  31. What’s going on inside the cell?

  32. How the fluid mosaic model is established

  33. Fluid Mosaic Model • helps keep the membrane firm and prevents it from beings too fluidy • and are surface identification markers and play a role in cell-cell (what kind of cell is this? Good or bad?) • -sugar molecule attached to a phospholipid • – sugar molecule attached to a protein embedded in the membrane –

  34. Proteins in the cell membrane

  35. By the end of this section you should be able to: • Apply knowledge of organic molecules – phospholipids, proteins, glycoproteins, glycolipids, and cholesterol – to explain the structure and function of the fluid mosaic model • Identify the hydrophobic and hydrophilic regions of the phospholipid bilayer • Explain why the cell membrane is described and selectively permeable • Describe passive transport processes including diffusion, osmosis and facilitated transport • Explain factors that affect the rate of diffusion across a cell membrane (temperature, size of molecule, charge of molecule, concentration gradient, pressure gradient) • Predict the effects of hypertonic, isotonic and hypotonic environments on osmosis in animal cells • Describe the active transport process in terms of: concentration gradients, use of channel or carrier proteins, use of energy, types/sizes of molecules transported • Describe active transport processes such as endocytosis and exocytosis in terms of use of energy, type/size of molecules transported

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