Exam 3 Essay ch. 7-9

Exam 3 Essay ch. 7-9 - 1. Discuss/explain the fluid mosaic...

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1. Discuss/explain the fluid mosaic model of membrane structure. a. According to the fluid mosaic model of S. J. Singer and Garth Nicolson , the biological membranes can be considered as a two-dimensional liquid where all lipid and protein molecules diffuse more or less freely. This picture may be valid in the space scale of 10 nm. However, the plasma membranes contain different structures or domains that can be classified as (a) protein-protein complexes; (b) lipid rafts , (c) pickets and fences formed by the actin-based cytoskeleton ; and (d) large stable structures, such as synapses or desmosomes. The fluid mosaic model can be seen when the membrane proteins of two cells (e.g., a human cell and a mouse cell) are tagged with different-coloured fluorescent labels. When the two cells are fused, the two colours intermix, indicating that the proteins are free to move in the 2D plane. 2. List and explain the roles (functions) of pthe plasma membrane a. a semipermeable lipid bilayer found in all cells . It contains a wide variety of biological molecules , primarily proteins and lipids , which are involved in a vast array of cellular processes such as cell adhesion, ion channel conductance and cell signaling. The plasma membrane also serves as the attachment point for both the intracellular cytoskeleton and, if present, the cell wall . The cell membrane surrounds the cytoplasm of a cell and, in animal cells, physically separates the intracellular components from the extracellular environment, thereby serving a function similar to that of skin . 3. List/explain/compare osmosis, diffusion, and active transport. a. Diffusion refers to the process by which molecules intermingle as a result of their kinetic energy of random motion. b. Osmosis - If two solutions of different concentration are separated by a semi- permeable membrane which is permeable to to the smaller solvent molecules but not to the larger solute molecules, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. c. involve properties of the membrane to selectively "pump" certain types of molecules across the membrane. 4. Explain movement across the membrane by channel proteins and carrier proteins. a. Carrier proteins are involved in active transport. These are specialized proteins of the cell membrane that move solutes across the cell membrane. They bind specific
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solutes or classes of solutes and undergo a conformational change when transporting the solute across the membrane. b. Both channel proteins and carrier proteins are involved in passive transport. Channel proteins assemble to form hydrohydrophilic pores or ion channels through the membrane lipid layer that selectively allows the passage of specific ions. In contrast to carrier proteins, solutes do not bind to the channel proteins nor do these proteins undergo a conformational change during ion transport. 5.
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Exam 3 Essay ch. 7-9 - 1. Discuss/explain the fluid mosaic...

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