Outline Chapter 7

Outline Chapter 7 - Chapter 7 Membrane Structure and...

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Chapter 7: Membrane Structure and Function I. Life at the Edge a. Plasma membrane – selective permeability – some substances cross more easily than others. b. One of the earliest episodes in evolution of life is the development of membrane where inside solution is different from outside solution II. Cellular membranes are fluid mosaics of lipids and proteins a. Lipids and proteins are staple ingredients. Carbs too. Phosopholipids most important. b. Amphipathic molecule – has hydrophilic and hydrophobic region. Fluid mosaic model – membrane is a fluid structure with mosaic of different proteins in a bilayer of phosophoolipids c. Membrane Models: Scientific Inquiry i. Membrane models built before being seen. In 1915 RBC membrane model already chemically analyzed. ii. If phospholipid bilayer is for membrane, then proteins location is confused. Heads are hydrophobic and so are outswards to water, hydrophilic away from water. Davson and Danielli 1935 – sandwich model – phosopholipid bilayer between 2 layers of proteins. iii. Problems with model – generalization of that membranes of cell are all identical. Plasma membrane is 7-8 nm whereas mitochondrial are a little different. Proteins in membrane are amphipathic as well. iv. Singer and Nicolson – proteins individually inserted into phosopholipid bilayer with hydrophilic regions protdruding = amximize hydrophilic regions of proteins and phosopholipids with water in cytosol and extracellular fluid whereas hydrophobic parts are hidden. v. Models are not better than the other since they’re all theories. d. The Fluidity of Membranes i. Held together by hydrophobic interactions, so lipids and proteins can shift laterally. Not usually flip flop across membrance since hydrophilic and hydrophobic portions would have to cross. ii. Very rapid lateral moving. Proteins are larger and move slower, but do drift. Move along cytoskeletal fibers by motor proteins connected to membrane proteins’ cytoplasmic regions. iii. Membrane remains fluid until temperature decreases and phospholipids settle into a closely packed arrangement and membrane solidifies – ex. Bacon grease solidifying when cools. iv. Membrane will remain fluid to a lower temperature if unsaturated – saturated vs. unsaturated – kinks and not. v. Cholesterol is bad because of this. Since it’s saturated fat, it has a lot of kinks in the chain vi. When membrane becomes solid, loses permeability and some of the enzymatic proteins become inactive.
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e. Membrane Proteins and Their Functions i. Membrane is collage of different proteins embedded in the fluid matrix of the lipid bilayer. More than 50 kinds of proteins found in RBC membranes. Phosopholipids may form main fabric of the membrane, but proteins determine most of the functions. Different types of cells has different types of proteins. ii.
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Outline Chapter 7 - Chapter 7 Membrane Structure and...

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