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Cell Membranes

Learn about the composition of cell membranes, types of transport mechanisms, and the role of biomolecules in cellular function.

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Cell Membranes

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  1. Cell Membranes • Structure and Function

  2. Quick review: Atoms bind together to make molecules.

  3. Complex carbohydrates are composed of simple sugars. Lipids are composed of fatty acids plus a polar head.

  4. Proteins are long chains of amino acids bound together. Nucleic acids are composed of chains of nucleotides.

  5. Building cell parts • The biological molecules are the basic building blocks of all cell parts. • Cell membranes are composed of proteins, lipids, and some complex carbohydrates.

  6. In our model of scale, that the cruise ship represented the cell. We’re now going to assemble large chain molecules into the parts of a cell.

  7. The Fluid Mosaic Model of the cell membrane Which classes of biomolecules are represented here? carbohydrate extracellular fluid (outside) __________ __________ glycoprotein protein phospholipid bilayer recognition protein binding site transport protein __________ _____________ pore ___________________ cytosol (inside)

  8. Membrane components: Lipid bilayer extracellular fluid (watery environment) ________________ phospholipid ___________________ bilayer ___________________ cytosol (watery environment)

  9. Membrane components: proteins The final shape of the protein determines its function. What conditions can denature proteins?

  10. Transport of Materials • Passive transport: • Simple diffusion • Facilitated diffusion • Osmosis • Energy-consuming transport: • Active transport • Exo/Endocytosis

  11. Diffusion 1 A drop of dye is placed in water. 2 Dye molecules diffuse into the water; water molecules diffuse into the dye. 3 Both dye molecules and water molecules Are evenly dispersed. drop of dye water molecule The movement of ____________ in solution from a ______ concentration of that molecule in the direction of a ______ concentration of that molecule until __________is reached.

  12. Diffusion across a membrane (extracellular fluid) lipid-soluble molecules and O2, CO2 O2 (cytosol)

  13. Facilitated diffusion H2O, ions Proteins form a hydrophilic channel. Cl– Cl– Cl– Cl– channel protein Cl– (cytosol) Why are channel proteins necessary to move hydrophilic ions through the membrane?

  14. Passive transport by facilitated diffusion carrier protein amino acids, sugars, small proteins (extracellular fluid) (cytosol) 1 Carrier protein has binding site for a specific molecule. 2 Molecule enters binding site. 3 Carrier protein changes shape, transporting molecule across membrane. 4 Carrier protein resumes original shape.

  15. Osmosis The _________ of ____________ through a semi-permeable _________. Water moves from its own high concentration to its own low concentration. Which direction will water move here?

  16. Tonicity If the contents of a cell and the fluid around the cell have the same concentration of dissolved solutes... ...the fluid is ____________ compared with the cell. Water moves in and out in equal amounts.

  17. Tonicity If the the fluid around the cell contains less dissolved solute than the fluid in the cell... ...the fluid is ____________ compared with the cell. More water enters the cell than leaves. The cell may swell to the point of bursting.

  18. Tonicity If the fluid around the cell contains more dissolved solute than the fluid inside the cell... ...the fluid is ___________ compared with the cell. More water leaves the cell than enters. The cell shrinks.

  19. Tonicity and plant cells cytosol central vacuole When water is plentiful, it fills the central vacuole, pushes the cytosol against the cell wall, and helps maintain the cell's shape.

  20. Tonicity and plant cells cell wall plasma membrane Plants wilt when water is scarce. They also wilt if salt is added to the soil. Why? When water is scarce, the central vacuole shrinks and the cell wall is unsupported.

  21. Active Transport 1 The transport protein binds both ATP and Ca2+. 2 Energy from ATP Changes the shape of the transport protein and moves the ion across the membrane. 3 The protein releases the ion and the remnants of ATP (ADP and P) and closes. (extracellular fluid) ATP ADP ATP Ca2+ (cytosol) P recognition site ATP binding site

  22. Endocytosis Phagocytosis is one example of endocytosis. (extracellular fluid) food particle pseudopods food vacuole (cytosol)

  23. Exocytosis secreted material plasma membrane (extracellular fluid) vesicle (cytosol) Material is enclosed in a vesicle that fuses with the plasma membrane, allowing its contents to diffuse out. 0.2 micrometer

  24. Recap • Cell parts, such as cell membranes, are made up of biological molecules. • The form and properties of the molecules determine their functions. • Cell membranes actively and passively control what materials enter and leave the cell.

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